[GitHub] [incubator-nuttx] adamfeuer commented on a change in pull request #1433: Main README converted to Markdown

[GitBox <gi...@apache.org>]

adamfeuer commented on a change in pull request #1433:
URL: https://github.com/apache/incubator-nuttx/pull/1433#discussion_r459802661



##########
File path: README.md
##########
@@ -0,0 +1,2513 @@
+# APACHE NUTTX (INCUBATING)
+
+* Introduction
+  - Incubation Status
+* Community
+  - Getting Help
+  - Mailing Lists
+  - Issue Tracker
+  - Source Code
+  - Website Source Code
+* Environments
+  - Installing Cygwin
+  - Ubuntu Bash under Windows 10
+  - Using macOS
+* Installation
+  - Download and Unpack
+  - Semi-Optional apps/ Package
+  - Installation Directories with Spaces in the Path
+  - Downloading from Repositories
+  - Related Repositories
+  - Notes about Header Files
+* Configuring NuttX
+  - Instantiating "Canned" Configurations
+  - Refreshing Configurations
+  - NuttX Configuration Tool
+  - Finding Selections in the Configuration Menus
+  - Reveal Hidden Configuration Options
+  - Make Sure that You are on the Right Platform
+  - Comparing Two Configurations
+  - Making defconfig Files
+  - Incompatibilities with Older Configurations
+  - NuttX Configuration Tool under DOS
+* Toolchains
+  - Cross-Development Toolchains
+  - NuttX Buildroot Toolchain
+* Shells
+* Building NuttX
+  - Building
+  - Re-building
+  - Build Targets and Options
+  - Native Windows Build
+  - Installing GNUWin32
+* Cygwin Build Problems
+  - Strange Path Problems
+  - Window Native Toolchain Issues
+* Documentation
+
+# INTRODUCTION
+
+Apache NuttX (Incubating) is a real-time operating system (RTOS) with an
+emphasis on standards compliance and small footprint.  Scalable from 8-bit
+to 32-bit microcontroller environments, the primary governing standards in
+NuttX are POSIX and ANSI standards. Additional standard APIs from Unix and
+other common RTOSs (such as VxWorks) are adopted for functionality not
+available under these standards, or for functionality that is not
+appropriate for deeply-embedded environments (such as fork()).
+
+Extensive documentation can be found on the project wiki:
+  <https://cwiki.apache.org/NUTTX/Nuttx>
+
+## Incubation Status
+
+Apache NuttX (Incubating) is an effort undergoing Incubation at The Apache
+Software Foundation (ASF), sponsored by the Incubator.  For more on our
+incubation effort, please see the file DISCLAIMER-WIP, in the same
+directory as this README.
+
+For brevity, the rest of this file will refer to it as Apache NuttX or
+simply NuttX.
+
+# COMMUNITY
+
+Every volunteer project obtains its strength from the people involved in
+it.  We invite you to participate as much or as little as you choose.
+
+We encourage you to:
+
+  - Use our project and provide feedback.
+  - Provide us with use-cases.
+  - Report bugs and submit patches.
+  - Contribute code or documentation.
+
+## Getting Help
+
+The best place to get help is the developer's mailing list.  Please see
+the following section:
+
+## Mailing Lists
+
+Get help using NuttX or contribute to the project on our mailing lists:
+
+  * <de...@nuttx.apache.org> is for people who want to contribute code to NuttX.
+    * To subscribe, send an email to <de...@nuttx.apache.org>.
+    * To unsubscribe, send an email to <de...@nuttx.apache.org>.
+    * View the archives at:
+      <https://www.mail-archive.com/dev@nuttx.apache.org/>
+
+  * <co...@nuttx.apache.org> is a read-only list that notifies subscribers
+  about commit messages and patches to NuttX.
+    * To subscribe, send an email to <co...@nuttx.apache.org>.
+    * To unsubscribe, send an email to <co...@nuttx.apache.org>.
+    * View the archives at:
+      <https://www.mail-archive.com/commits@nuttx.apache.org/>
+
+## Issue Tracker
+
+### Bug Reports:
+
+Found bug? Send an email to the dev list: <de...@nuttx.apache.org>
+
+Before submitting an issue, please:
+
+  - Verify that the bug does in fact exist. 
+  
+  - Search the mailing list archives to verify there is no existing issue
+    reporting the bug you've found.
+ 
+  - Consider tracking down the bug yourself in the NuttX source code and
+    submitting a patch along with your bug report.  This is a great time
+    saver for the NuttX developers and helps ensure the bug will be fixed
+    quickly.
+  
+### Feature Requests:
+  
+Enhancement requests for new features are also welcome. The more concrete
+and rational the request is, the greater the chance it will incorporated
+into future releases.
+
+## Source Code
+
+The project sources are in two Git repositories.  The core OS is in
+incubator-nuttx and the apps repository is in incubator-nuttx-apps.  These
+are housed in GitBox on ASF servers and also mirrored at GitHub.  These
+are kept in sync, so you can use whichever option you prefer.
+
+  - NuttX core OS repository:
+    
+    - Primary:
+      <https://gitbox.apache.org/repos/asf?p=incubator-nuttx.git>
+    
+    - GitHub Mirror:
+      <https://github.com/apache/incubator-nuttx>
+  
+  - Apps repository:
+    
+    - Primary:
+      <https://gitbox.apache.org/repos/asf?p=incubator-nuttx-apps.git>
+    
+    - GitHub Mirror:
+      <https://github.com/apache/incubator-nuttx-apps>
+
+## Website Source Code
+
+The project website sources are accessible via the website source code
+  repository which is also mirrored in GitHub:
+
+- Primary:
+  <https://gitbox.apache.org/repos/asf?p=incubator-nuttx-website.git>
+
+- GitHub Mirror:
+  <https://github.com/apache/incubator-nuttx-website>
+
+# ENVIRONMENTS
+
+  NuttX requires a POSIX development environment such as you would find under
+  Linux or macOS.  NuttX may also be installed and built on Windows system
+  if you also provide such a POSIX development environment.  Options for a
+  POSIX development environment under Windows include:
+
+  - An installation of Linux on a virtual machine (VM) in Windows.  I have
+    not been happy using a VM myself.  I have had stability problems with
+    open source VMs and commercial VMs cost more than I want to spend.
+    Sharing files with Linux running in a VM is awkward;  sharing devices
+    connected to the Windows box with Linux in a VM is, at the very least,
+    confusing;  Using Windows tools (such as Segger J-Link) with files
+    built under the Linux VM is not a possibility.
+
+  - The Cygwin environment.  Instructions for installation of Cygwin on a
+    Windows system are provided in the following paragraph, "Installing
+    Cygwin".  Cygwin is a mature, well-tested, and very convenient
+    environment.  It is especially convenient if you  need to
+    integrate with Windows tools and files.  Downsides are that the
+    installation time is very long and the compile times are slow.
+
+  - Ubuntu/Bash shell under Windows 10.  This is a new option under
+    Windows 10.  See the section "Ubuntu Bash under Windows 10" below.
+    This is an improvement over Cygwin if your concern is compile time;
+    its build performance is comparable to native Linux, certainly better
+    than the Cygwin build time.  It also installs in a tiny fraction of
+    the time as Cygwin, perhaps 20 minutes for the basic Ubuntu install
+    (vs. more than a day for the complete Cygwin install).
+  
+    There have been even more recent ports of Linux environment to
+    Windows.  I need to update this section to include some mention of
+    these alternatives.
+
+  - The MSYS environment.  MSYS derives from an older version of Cygwin
+    simplified and adapted to work more naturally in the Windows
+    environment.  See <http://www.mingw.org/wiki/MSYS> if you are
+    interested in using MSYS.  The advantages of the MSYS environment is
+    that it is better integrted with the native Windows environment and
+    lighter weight; it uses only a  minimal number of add-on POSIX-land
+    tools.
+  
+    The download link in that Wiki takes you to the SourceForge download
+    site.  The SourceForge MSYS project has been stagnant for some time.
+    The MSYS project has more recently moved to
+    <http://odsn.net/projects/sfnet_mingwbundle>.  Downloads of current .zip
+    files are available there but no instructions for the installation.
+
+  - MSYS2 appears to be a re-write of MSYS based on a newer version of
+    Cygwin.  Is it available at <https://www.msys2.org>.  A windows
+    installer is available at that site along with very good installation
+    instructions.  The download is relatively quick (at least compared to
+    Cygwin) and the 'pacman' package management tool supports supports
+    simple system updates.  For example, 'pacman -S git' will install the
+    GIT command line utilities.
+
+  - Other POSIX environments.  Check out:
+    
+    - UnxUtils: <https://sourceforge.net/projects/unxutils/>,
+      <https://en.wikipedia.org/wiki/UnxUtils>
+    - MobaXterm: <https://mobaxterm.mobatek.net/>
+    - Gow: <https://github.com/bmatzelle/gow/wiki>
+  
+    **Disclaimer**:  In principle, these should work.  However, I have never
+    used any of these environments and cannot guarantee that there is
+    not some less-than-obvious issues.
+  
+NuttX can also be installed and built on a native Windows system, but with
+some potential tool-related issues (see the discussion "Native Windows
+Build" under "Building NuttX" below).  GNUWin32 is used to provide
+compatible native windows tools.
+
+## Installing Cygwin
+
+Installing Cygwin on your Windows PC is simple, but time consuming.  See
+<http://www.cygwin.com/> for installation instructions. Basically you just
+need to download a tiny setup.exe program and it does the real, network
+installation for you.
+
+Some Cygwin installation tips:
+
+  1. Install at `C:\cygwin`
+  
+  2. Install **everything**:  "Only the minimal base packages from the
+     Cygwin distribution are installed by default. Clicking on categories
+     and packages in the setup.exe package installation screen will
+     provide you with the ability to control what is installed or updated.
+     Clicking on the "Default" field next to the "All" category will
+     provide you with the opportunity to install every Cygwin package.
+     Be advised that this will download and install hundreds of megabytes
+     to your computer."
+   
+If you use the "default" installation, you will be missing many
+of the Cygwin utilities that you will need to build NuttX.  The
+build will fail in numerous places because of missing packages.
+
+NOTE: The last time I installed **everything**, the download was
+about 5GiB.  The server I selected was also very slow so it took
+over a day to do the whole install!
+
+NOTE: You don't really have to install **everything** but I cannot
+answer the question "Then what should I install?"  I don't know
+the answer to that and so will continue to recommend installing
+**everything**.
+
+You should certainly be able to omit "Science", "Math", and
+"Publishing".  You can try omitting KDE, Gnome, GTK, and other
+graphics packages if you don't plan to use them.
+
+Perhaps a minimum set would be those packages listed below for the
+"Ubuntu Bash under Windows 10" installation?
+
+**UPDATE**:  Sergey Frolov had success with the following minimal
+Cygwin configuration:
+   
+   1. After starting the Cygwin installer, keep the recommended
+      packages that are pre-selected in the default configuration.
+   
+   2. Using the installation tools, add the following packages:
+      
+        make (GNU make)  bison        libgmp3-dev

Review comment:
       @v01d This needs to be indented 4 spaces to make it a preformatted block, I think there's a few too many spaces here.

##########
File path: README.md
##########
@@ -0,0 +1,2513 @@
+# APACHE NUTTX (INCUBATING)
+
+* Introduction
+  - Incubation Status
+* Community
+  - Getting Help
+  - Mailing Lists
+  - Issue Tracker
+  - Source Code
+  - Website Source Code
+* Environments
+  - Installing Cygwin
+  - Ubuntu Bash under Windows 10
+  - Using macOS
+* Installation
+  - Download and Unpack
+  - Semi-Optional apps/ Package
+  - Installation Directories with Spaces in the Path
+  - Downloading from Repositories
+  - Related Repositories
+  - Notes about Header Files
+* Configuring NuttX
+  - Instantiating "Canned" Configurations
+  - Refreshing Configurations
+  - NuttX Configuration Tool
+  - Finding Selections in the Configuration Menus
+  - Reveal Hidden Configuration Options
+  - Make Sure that You are on the Right Platform
+  - Comparing Two Configurations
+  - Making defconfig Files
+  - Incompatibilities with Older Configurations
+  - NuttX Configuration Tool under DOS
+* Toolchains
+  - Cross-Development Toolchains
+  - NuttX Buildroot Toolchain
+* Shells
+* Building NuttX
+  - Building
+  - Re-building
+  - Build Targets and Options
+  - Native Windows Build
+  - Installing GNUWin32
+* Cygwin Build Problems
+  - Strange Path Problems
+  - Window Native Toolchain Issues
+* Documentation
+
+# INTRODUCTION
+
+Apache NuttX (Incubating) is a real-time operating system (RTOS) with an
+emphasis on standards compliance and small footprint.  Scalable from 8-bit
+to 32-bit microcontroller environments, the primary governing standards in
+NuttX are POSIX and ANSI standards. Additional standard APIs from Unix and
+other common RTOSs (such as VxWorks) are adopted for functionality not
+available under these standards, or for functionality that is not
+appropriate for deeply-embedded environments (such as fork()).
+
+Extensive documentation can be found on the project wiki:
+  <https://cwiki.apache.org/NUTTX/Nuttx>
+
+## Incubation Status
+
+Apache NuttX (Incubating) is an effort undergoing Incubation at The Apache
+Software Foundation (ASF), sponsored by the Incubator.  For more on our
+incubation effort, please see the file DISCLAIMER-WIP, in the same
+directory as this README.
+
+For brevity, the rest of this file will refer to it as Apache NuttX or
+simply NuttX.
+
+# COMMUNITY
+
+Every volunteer project obtains its strength from the people involved in
+it.  We invite you to participate as much or as little as you choose.
+
+We encourage you to:
+
+  - Use our project and provide feedback.
+  - Provide us with use-cases.
+  - Report bugs and submit patches.
+  - Contribute code or documentation.
+
+## Getting Help
+
+The best place to get help is the developer's mailing list.  Please see
+the following section:
+
+## Mailing Lists
+
+Get help using NuttX or contribute to the project on our mailing lists:
+
+  * <de...@nuttx.apache.org> is for people who want to contribute code to NuttX.
+    * To subscribe, send an email to <de...@nuttx.apache.org>.
+    * To unsubscribe, send an email to <de...@nuttx.apache.org>.
+    * View the archives at:
+      <https://www.mail-archive.com/dev@nuttx.apache.org/>
+
+  * <co...@nuttx.apache.org> is a read-only list that notifies subscribers
+  about commit messages and patches to NuttX.
+    * To subscribe, send an email to <co...@nuttx.apache.org>.
+    * To unsubscribe, send an email to <co...@nuttx.apache.org>.
+    * View the archives at:
+      <https://www.mail-archive.com/commits@nuttx.apache.org/>
+
+## Issue Tracker
+
+### Bug Reports:
+
+Found bug? Send an email to the dev list: <de...@nuttx.apache.org>
+
+Before submitting an issue, please:
+
+  - Verify that the bug does in fact exist. 
+  
+  - Search the mailing list archives to verify there is no existing issue
+    reporting the bug you've found.
+ 
+  - Consider tracking down the bug yourself in the NuttX source code and
+    submitting a patch along with your bug report.  This is a great time
+    saver for the NuttX developers and helps ensure the bug will be fixed
+    quickly.
+  
+### Feature Requests:
+  
+Enhancement requests for new features are also welcome. The more concrete
+and rational the request is, the greater the chance it will incorporated
+into future releases.
+
+## Source Code
+
+The project sources are in two Git repositories.  The core OS is in
+incubator-nuttx and the apps repository is in incubator-nuttx-apps.  These
+are housed in GitBox on ASF servers and also mirrored at GitHub.  These
+are kept in sync, so you can use whichever option you prefer.
+
+  - NuttX core OS repository:
+    
+    - Primary:
+      <https://gitbox.apache.org/repos/asf?p=incubator-nuttx.git>
+    
+    - GitHub Mirror:
+      <https://github.com/apache/incubator-nuttx>
+  
+  - Apps repository:
+    
+    - Primary:
+      <https://gitbox.apache.org/repos/asf?p=incubator-nuttx-apps.git>
+    
+    - GitHub Mirror:
+      <https://github.com/apache/incubator-nuttx-apps>
+
+## Website Source Code
+
+The project website sources are accessible via the website source code
+  repository which is also mirrored in GitHub:
+
+- Primary:
+  <https://gitbox.apache.org/repos/asf?p=incubator-nuttx-website.git>
+
+- GitHub Mirror:
+  <https://github.com/apache/incubator-nuttx-website>
+
+# ENVIRONMENTS
+
+  NuttX requires a POSIX development environment such as you would find under
+  Linux or macOS.  NuttX may also be installed and built on Windows system
+  if you also provide such a POSIX development environment.  Options for a
+  POSIX development environment under Windows include:
+
+  - An installation of Linux on a virtual machine (VM) in Windows.  I have
+    not been happy using a VM myself.  I have had stability problems with
+    open source VMs and commercial VMs cost more than I want to spend.
+    Sharing files with Linux running in a VM is awkward;  sharing devices
+    connected to the Windows box with Linux in a VM is, at the very least,
+    confusing;  Using Windows tools (such as Segger J-Link) with files
+    built under the Linux VM is not a possibility.
+
+  - The Cygwin environment.  Instructions for installation of Cygwin on a
+    Windows system are provided in the following paragraph, "Installing
+    Cygwin".  Cygwin is a mature, well-tested, and very convenient
+    environment.  It is especially convenient if you  need to
+    integrate with Windows tools and files.  Downsides are that the
+    installation time is very long and the compile times are slow.
+
+  - Ubuntu/Bash shell under Windows 10.  This is a new option under
+    Windows 10.  See the section "Ubuntu Bash under Windows 10" below.
+    This is an improvement over Cygwin if your concern is compile time;
+    its build performance is comparable to native Linux, certainly better
+    than the Cygwin build time.  It also installs in a tiny fraction of
+    the time as Cygwin, perhaps 20 minutes for the basic Ubuntu install
+    (vs. more than a day for the complete Cygwin install).
+  
+    There have been even more recent ports of Linux environment to
+    Windows.  I need to update this section to include some mention of
+    these alternatives.
+
+  - The MSYS environment.  MSYS derives from an older version of Cygwin
+    simplified and adapted to work more naturally in the Windows
+    environment.  See <http://www.mingw.org/wiki/MSYS> if you are
+    interested in using MSYS.  The advantages of the MSYS environment is
+    that it is better integrted with the native Windows environment and
+    lighter weight; it uses only a  minimal number of add-on POSIX-land
+    tools.
+  
+    The download link in that Wiki takes you to the SourceForge download
+    site.  The SourceForge MSYS project has been stagnant for some time.
+    The MSYS project has more recently moved to
+    <http://odsn.net/projects/sfnet_mingwbundle>.  Downloads of current .zip
+    files are available there but no instructions for the installation.
+
+  - MSYS2 appears to be a re-write of MSYS based on a newer version of
+    Cygwin.  Is it available at <https://www.msys2.org>.  A windows
+    installer is available at that site along with very good installation
+    instructions.  The download is relatively quick (at least compared to
+    Cygwin) and the 'pacman' package management tool supports supports
+    simple system updates.  For example, 'pacman -S git' will install the
+    GIT command line utilities.
+
+  - Other POSIX environments.  Check out:
+    
+    - UnxUtils: <https://sourceforge.net/projects/unxutils/>,
+      <https://en.wikipedia.org/wiki/UnxUtils>
+    - MobaXterm: <https://mobaxterm.mobatek.net/>
+    - Gow: <https://github.com/bmatzelle/gow/wiki>
+  
+    **Disclaimer**:  In principle, these should work.  However, I have never
+    used any of these environments and cannot guarantee that there is
+    not some less-than-obvious issues.
+  
+NuttX can also be installed and built on a native Windows system, but with
+some potential tool-related issues (see the discussion "Native Windows
+Build" under "Building NuttX" below).  GNUWin32 is used to provide
+compatible native windows tools.
+
+## Installing Cygwin
+
+Installing Cygwin on your Windows PC is simple, but time consuming.  See
+<http://www.cygwin.com/> for installation instructions. Basically you just
+need to download a tiny setup.exe program and it does the real, network
+installation for you.
+
+Some Cygwin installation tips:
+
+  1. Install at `C:\cygwin`
+  
+  2. Install **everything**:  "Only the minimal base packages from the
+     Cygwin distribution are installed by default. Clicking on categories
+     and packages in the setup.exe package installation screen will
+     provide you with the ability to control what is installed or updated.
+     Clicking on the "Default" field next to the "All" category will
+     provide you with the opportunity to install every Cygwin package.
+     Be advised that this will download and install hundreds of megabytes
+     to your computer."
+   
+If you use the "default" installation, you will be missing many
+of the Cygwin utilities that you will need to build NuttX.  The
+build will fail in numerous places because of missing packages.
+
+NOTE: The last time I installed **everything**, the download was
+about 5GiB.  The server I selected was also very slow so it took
+over a day to do the whole install!
+
+NOTE: You don't really have to install **everything** but I cannot
+answer the question "Then what should I install?"  I don't know
+the answer to that and so will continue to recommend installing
+**everything**.
+
+You should certainly be able to omit "Science", "Math", and
+"Publishing".  You can try omitting KDE, Gnome, GTK, and other
+graphics packages if you don't plan to use them.
+
+Perhaps a minimum set would be those packages listed below for the
+"Ubuntu Bash under Windows 10" installation?
+
+**UPDATE**:  Sergey Frolov had success with the following minimal
+Cygwin configuration:
+   
+   1. After starting the Cygwin installer, keep the recommended
+      packages that are pre-selected in the default configuration.
+   
+   2. Using the installation tools, add the following packages:
+      
+        make (GNU make)  bison        libgmp3-dev
+        gcc-core         byacc        libmpfr-dev
+        gcc-g++          gperf        libmpc-dev
+        flex             gdb          automake-1.15
+        libncurses-dev   libgmp-dev
+   
+After installing Cygwin, you will get lots of links for installed
+tools and shells.  I use the RXVT native shell.  It is fast and reliable
+and does not require you to run the Cygwin X server (which is neither
+fast nor reliable).  Unless otherwise noted, the rest of these
+instructions assume that you are at a bash command line prompt in
+either Linux or in Cygwin shell.
+
+## Using MSYS
+
+MSYS is an environment the derives from Cygwin.  Thus, most things said
+about Cygwin apply equally to MSYS.  This section will, then, focus on
+the differences when using MSYS, specifically MSYS2.
+
+Here is it assumed that you have already downloaded and installed MSYS2
+from https://www.msys2.org using the windows installer available at that
+location.  It is also assumed that you have brought in the necessary
+tools using the 'pacman' package management tool Tools needed including:
+
+  pacman -S git

Review comment:
       @v01d Indent level needs to be four spaces so this can be a preformatted block, see the correct block below.

##########
File path: README.md
##########
@@ -0,0 +1,2513 @@
+# APACHE NUTTX (INCUBATING)
+
+* Introduction
+  - Incubation Status
+* Community
+  - Getting Help
+  - Mailing Lists
+  - Issue Tracker
+  - Source Code
+  - Website Source Code
+* Environments
+  - Installing Cygwin
+  - Ubuntu Bash under Windows 10
+  - Using macOS
+* Installation
+  - Download and Unpack
+  - Semi-Optional apps/ Package
+  - Installation Directories with Spaces in the Path
+  - Downloading from Repositories
+  - Related Repositories
+  - Notes about Header Files
+* Configuring NuttX
+  - Instantiating "Canned" Configurations
+  - Refreshing Configurations
+  - NuttX Configuration Tool
+  - Finding Selections in the Configuration Menus
+  - Reveal Hidden Configuration Options
+  - Make Sure that You are on the Right Platform
+  - Comparing Two Configurations
+  - Making defconfig Files
+  - Incompatibilities with Older Configurations
+  - NuttX Configuration Tool under DOS
+* Toolchains
+  - Cross-Development Toolchains
+  - NuttX Buildroot Toolchain
+* Shells
+* Building NuttX
+  - Building
+  - Re-building
+  - Build Targets and Options
+  - Native Windows Build
+  - Installing GNUWin32
+* Cygwin Build Problems
+  - Strange Path Problems
+  - Window Native Toolchain Issues
+* Documentation
+
+# INTRODUCTION
+
+Apache NuttX (Incubating) is a real-time operating system (RTOS) with an
+emphasis on standards compliance and small footprint.  Scalable from 8-bit
+to 32-bit microcontroller environments, the primary governing standards in
+NuttX are POSIX and ANSI standards. Additional standard APIs from Unix and
+other common RTOSs (such as VxWorks) are adopted for functionality not
+available under these standards, or for functionality that is not
+appropriate for deeply-embedded environments (such as fork()).
+
+Extensive documentation can be found on the project wiki:
+  <https://cwiki.apache.org/NUTTX/Nuttx>
+
+## Incubation Status
+
+Apache NuttX (Incubating) is an effort undergoing Incubation at The Apache
+Software Foundation (ASF), sponsored by the Incubator.  For more on our
+incubation effort, please see the file DISCLAIMER-WIP, in the same
+directory as this README.
+
+For brevity, the rest of this file will refer to it as Apache NuttX or
+simply NuttX.
+
+# COMMUNITY
+
+Every volunteer project obtains its strength from the people involved in
+it.  We invite you to participate as much or as little as you choose.
+
+We encourage you to:
+
+  - Use our project and provide feedback.
+  - Provide us with use-cases.
+  - Report bugs and submit patches.
+  - Contribute code or documentation.
+
+## Getting Help
+
+The best place to get help is the developer's mailing list.  Please see
+the following section:
+
+## Mailing Lists
+
+Get help using NuttX or contribute to the project on our mailing lists:
+
+  * <de...@nuttx.apache.org> is for people who want to contribute code to NuttX.
+    * To subscribe, send an email to <de...@nuttx.apache.org>.
+    * To unsubscribe, send an email to <de...@nuttx.apache.org>.
+    * View the archives at:
+      <https://www.mail-archive.com/dev@nuttx.apache.org/>
+
+  * <co...@nuttx.apache.org> is a read-only list that notifies subscribers
+  about commit messages and patches to NuttX.
+    * To subscribe, send an email to <co...@nuttx.apache.org>.
+    * To unsubscribe, send an email to <co...@nuttx.apache.org>.
+    * View the archives at:
+      <https://www.mail-archive.com/commits@nuttx.apache.org/>
+
+## Issue Tracker
+
+### Bug Reports:
+
+Found bug? Send an email to the dev list: <de...@nuttx.apache.org>
+
+Before submitting an issue, please:
+
+  - Verify that the bug does in fact exist. 
+  
+  - Search the mailing list archives to verify there is no existing issue
+    reporting the bug you've found.
+ 
+  - Consider tracking down the bug yourself in the NuttX source code and
+    submitting a patch along with your bug report.  This is a great time
+    saver for the NuttX developers and helps ensure the bug will be fixed
+    quickly.
+  
+### Feature Requests:
+  
+Enhancement requests for new features are also welcome. The more concrete
+and rational the request is, the greater the chance it will incorporated
+into future releases.
+
+## Source Code
+
+The project sources are in two Git repositories.  The core OS is in
+incubator-nuttx and the apps repository is in incubator-nuttx-apps.  These
+are housed in GitBox on ASF servers and also mirrored at GitHub.  These
+are kept in sync, so you can use whichever option you prefer.
+
+  - NuttX core OS repository:
+    
+    - Primary:
+      <https://gitbox.apache.org/repos/asf?p=incubator-nuttx.git>
+    
+    - GitHub Mirror:
+      <https://github.com/apache/incubator-nuttx>
+  
+  - Apps repository:
+    
+    - Primary:
+      <https://gitbox.apache.org/repos/asf?p=incubator-nuttx-apps.git>
+    
+    - GitHub Mirror:
+      <https://github.com/apache/incubator-nuttx-apps>
+
+## Website Source Code
+
+The project website sources are accessible via the website source code
+  repository which is also mirrored in GitHub:
+
+- Primary:
+  <https://gitbox.apache.org/repos/asf?p=incubator-nuttx-website.git>
+
+- GitHub Mirror:
+  <https://github.com/apache/incubator-nuttx-website>
+
+# ENVIRONMENTS
+
+  NuttX requires a POSIX development environment such as you would find under
+  Linux or macOS.  NuttX may also be installed and built on Windows system
+  if you also provide such a POSIX development environment.  Options for a
+  POSIX development environment under Windows include:
+
+  - An installation of Linux on a virtual machine (VM) in Windows.  I have
+    not been happy using a VM myself.  I have had stability problems with
+    open source VMs and commercial VMs cost more than I want to spend.
+    Sharing files with Linux running in a VM is awkward;  sharing devices
+    connected to the Windows box with Linux in a VM is, at the very least,
+    confusing;  Using Windows tools (such as Segger J-Link) with files
+    built under the Linux VM is not a possibility.
+
+  - The Cygwin environment.  Instructions for installation of Cygwin on a
+    Windows system are provided in the following paragraph, "Installing
+    Cygwin".  Cygwin is a mature, well-tested, and very convenient
+    environment.  It is especially convenient if you  need to
+    integrate with Windows tools and files.  Downsides are that the
+    installation time is very long and the compile times are slow.
+
+  - Ubuntu/Bash shell under Windows 10.  This is a new option under
+    Windows 10.  See the section "Ubuntu Bash under Windows 10" below.
+    This is an improvement over Cygwin if your concern is compile time;
+    its build performance is comparable to native Linux, certainly better
+    than the Cygwin build time.  It also installs in a tiny fraction of
+    the time as Cygwin, perhaps 20 minutes for the basic Ubuntu install
+    (vs. more than a day for the complete Cygwin install).
+  
+    There have been even more recent ports of Linux environment to
+    Windows.  I need to update this section to include some mention of
+    these alternatives.
+
+  - The MSYS environment.  MSYS derives from an older version of Cygwin
+    simplified and adapted to work more naturally in the Windows
+    environment.  See <http://www.mingw.org/wiki/MSYS> if you are
+    interested in using MSYS.  The advantages of the MSYS environment is
+    that it is better integrted with the native Windows environment and
+    lighter weight; it uses only a  minimal number of add-on POSIX-land
+    tools.
+  
+    The download link in that Wiki takes you to the SourceForge download
+    site.  The SourceForge MSYS project has been stagnant for some time.
+    The MSYS project has more recently moved to
+    <http://odsn.net/projects/sfnet_mingwbundle>.  Downloads of current .zip
+    files are available there but no instructions for the installation.
+
+  - MSYS2 appears to be a re-write of MSYS based on a newer version of
+    Cygwin.  Is it available at <https://www.msys2.org>.  A windows
+    installer is available at that site along with very good installation
+    instructions.  The download is relatively quick (at least compared to
+    Cygwin) and the 'pacman' package management tool supports supports
+    simple system updates.  For example, 'pacman -S git' will install the
+    GIT command line utilities.
+
+  - Other POSIX environments.  Check out:
+    
+    - UnxUtils: <https://sourceforge.net/projects/unxutils/>,
+      <https://en.wikipedia.org/wiki/UnxUtils>
+    - MobaXterm: <https://mobaxterm.mobatek.net/>
+    - Gow: <https://github.com/bmatzelle/gow/wiki>
+  
+    **Disclaimer**:  In principle, these should work.  However, I have never
+    used any of these environments and cannot guarantee that there is
+    not some less-than-obvious issues.
+  
+NuttX can also be installed and built on a native Windows system, but with
+some potential tool-related issues (see the discussion "Native Windows
+Build" under "Building NuttX" below).  GNUWin32 is used to provide
+compatible native windows tools.
+
+## Installing Cygwin
+
+Installing Cygwin on your Windows PC is simple, but time consuming.  See
+<http://www.cygwin.com/> for installation instructions. Basically you just
+need to download a tiny setup.exe program and it does the real, network
+installation for you.
+
+Some Cygwin installation tips:
+
+  1. Install at `C:\cygwin`
+  
+  2. Install **everything**:  "Only the minimal base packages from the
+     Cygwin distribution are installed by default. Clicking on categories
+     and packages in the setup.exe package installation screen will
+     provide you with the ability to control what is installed or updated.
+     Clicking on the "Default" field next to the "All" category will
+     provide you with the opportunity to install every Cygwin package.
+     Be advised that this will download and install hundreds of megabytes
+     to your computer."
+   
+If you use the "default" installation, you will be missing many
+of the Cygwin utilities that you will need to build NuttX.  The
+build will fail in numerous places because of missing packages.
+
+NOTE: The last time I installed **everything**, the download was
+about 5GiB.  The server I selected was also very slow so it took
+over a day to do the whole install!
+
+NOTE: You don't really have to install **everything** but I cannot
+answer the question "Then what should I install?"  I don't know
+the answer to that and so will continue to recommend installing
+**everything**.
+
+You should certainly be able to omit "Science", "Math", and
+"Publishing".  You can try omitting KDE, Gnome, GTK, and other
+graphics packages if you don't plan to use them.
+
+Perhaps a minimum set would be those packages listed below for the
+"Ubuntu Bash under Windows 10" installation?
+
+**UPDATE**:  Sergey Frolov had success with the following minimal
+Cygwin configuration:
+   
+   1. After starting the Cygwin installer, keep the recommended
+      packages that are pre-selected in the default configuration.
+   
+   2. Using the installation tools, add the following packages:
+      
+        make (GNU make)  bison        libgmp3-dev
+        gcc-core         byacc        libmpfr-dev
+        gcc-g++          gperf        libmpc-dev
+        flex             gdb          automake-1.15
+        libncurses-dev   libgmp-dev
+   
+After installing Cygwin, you will get lots of links for installed
+tools and shells.  I use the RXVT native shell.  It is fast and reliable
+and does not require you to run the Cygwin X server (which is neither
+fast nor reliable).  Unless otherwise noted, the rest of these
+instructions assume that you are at a bash command line prompt in
+either Linux or in Cygwin shell.
+
+## Using MSYS
+
+MSYS is an environment the derives from Cygwin.  Thus, most things said
+about Cygwin apply equally to MSYS.  This section will, then, focus on
+the differences when using MSYS, specifically MSYS2.
+
+Here is it assumed that you have already downloaded and installed MSYS2
+from https://www.msys2.org using the windows installer available at that
+location.  It is also assumed that you have brought in the necessary
+tools using the 'pacman' package management tool Tools needed including:
+
+  pacman -S git
+  pacman -S make
+  pacman -S gcc
+  pacman -S gdb
+
+And possibly others depending upon your usage.  Then you will need to
+build and install kconfig-frontends per the instructions of the top-level
+README.txt file in the tools repository.  This requires the following
+additional tools:
+
+    pacman -S bison
+    pacman -S gperf
+    pacman -S ncurses-devel
+    pacman -S automake-wrapper
+    pacman -S autoconf
+    pacman -S pkg-config
+
+Because of some versioning issues, I had to run 'aclocal' prior to
+running the kconfig-frontends configure script.  See "Configuring NuttX"
+below for further information.
+
+Unlike Cygwin, MSYS does not support symbolic links.  The 'ln -s' command
+will, in fact, copy a directory!  This means that you Make.defs file will
+have to include definitions like:
+
+    ifeq ($(CONFIG_WINDOWS_MSYS),y)
+      DIRLINK = $(TOPDIR)/tools/copydir.sh
+      DIRUNLINK = $(TOPDIR)/tools/unlink.sh
+    endif
+
+This will force the directory copies to work in a way that can be handled
+by the NuttX build system.  NOTE:  The default link.sh script has been
+updated so that is should now be MSYS2 compatible.  The above is preferred
+but no longer necessary in the Make.defs file.
+
+To build the simulator under MSYS, you also need:
+
+    pacman -S zlib-devel
+
+It appears that you cannot use directory names with spaces in them like
+"/c/Program\ Files \(86\)" in the MSYS path variable.  I worked around this
+by create Windows junctions like this:
+
+  1. Open the a windows command terminal,
+  
+  2. CD to `c:\msys64`, then
+  
+  3. `mklink /j programfiles "C:/Program\ Files"` and
+  
+  4. `mklink /j programfiles86 "C:/Program\ Files\ \(x86\)"`
+     
+     They then show up as `/programfiles` and `/programfiles86` with the MSYS2
+     sandbox.  Those paths can then be used with the PATH variable.  I had
+     to do something similar for the path to the GNU Tools "ARM Embedded
+     Toolchain" which also has spaces in the path name.
+
+## Ubuntu Bash under Windows 10
+
+A better version of a command-line only Ubuntu under Windows 10 (beta)
+has recently been made available from Microsoft.
+
+### Installation
+
+Installation instructions abound on the Internet complete with screen
+shots.  I will attempt to duplicate those instructions in full here.
+Here are the simplified installation steps:
+
+  - Open *Settings*.
+  
+  - Click on *Update & security*.
+  
+  - Click on *For Developers*.
+  
+  - Under *Use developer features*, select the *Developer mode* option to
+    setup the environment to install Bash.
+  
+  - A message box should pop up.  Click *Yes* to turn on developer mode.
+  
+  - After the necessary components install, you'll need to restart your
+    computer.
+    
+    Once your computer reboots:
+  
+  - Open *Control Panel*.
+  
+  - Click on *Programs*.
+  
+  - Click on *Turn Windows features on or off*.
+  
+  - A list of features will pop up, check the *Windows Subsystem for Linux
+    (beta)* option.
+  
+  - Click *OK*.
+  
+  - Once the components installed on your computer, click the *Restart
+    now* button to complete the task.
+    
+    After your computer restarts, you will notice that Bash will not appear in
+    the *Recently added* list of apps, this is because Bash isn't actually
+    installed yet. Now that you have setup the necessary components, use the
+    following steps to complete the installation of Bash:
+  
+  - Open *Start*, do a search for `bash.exe`, and press *Enter*.
+  
+  - On the command prompt, type `y` and press Enter to download and install
+    Bash from the Windows Store.  This will take awhile.
+  
+  - Then you'll need to create a default UNIX user account. This account
+    doesn't have to be the same as your Windows account. Enter the
+    username in the required field and press Enter (you can't use the
+    username `admin`).
+  
+  - Close the `bash.exe` command prompt.
+  
+  Now that you completed the installation and setup, you can open the Bash
+  tool from the Start menu like you would with any other app.
+
+### Accessing Windows Files from Ubuntu
+
+File systems will be mounted under `/mnt` so for example `C:\Program Files`
+appears at `/mnt/c/Program Files`.  This is as opposed to Cygwin where
+the same directory would appear at `/cygdrive/c/Program Files`.
+
+With these differences (perhaps a few other Windows quirks) the Ubuntu
+install works just like Ubuntu running natively on your PC.
+
+A good tip for file sharing is to use symbolic links within your Ubuntu
+home directory.  For example, suppose you have your `projects` directory
+at `C:\Documents\projects`.  Then you can set up a link to the `projects/`
+directory in your Ubuntu directory like:
+
+    ln -s /mnt/c/Documents/projects projects
+
+### Accessing Ubuntu Files From Windows
+
+In Ubuntu Userspace for Windows, the Ubuntu file system root directory is
+at:
+
+    %localappdata%\lxss\rootfs
+
+Or
+
+    C:\Users\Username\AppData\Local\lxss\rootfs
+
+However, I am unable to see my files under the rootfs\home directory.
+After some looking around, I find the home directory
+`%localappdata%\lxss\home`.
+
+With that trick access to the `/home` directory, you should actually be
+able to use Windows tools outside of the Ubuntu sandbox with versions of
+NuttX built within the sandbox using that path.
+
+### Executing Windows Tools from Ubuntu
+
+You can also execute Windows tools from within the Ubuntu sandbox:
+
+    /mnt/c/Program\ Files\ \(x86\)/Microchip/xc32/v1.43/bin/xc32-gcc.exe --version
+    Unable to translate current working directory. Using C:\WINDOWS\System32
+    xc32-gcc.exe (Microchip Technology) 4.8.3 MPLAB XC32 Compiler v1.43 Build date: Mar  1 2017
+    ...
+
+The error message indicates that there are more issues:  You cannot mix
+Windows tools that use Windows style paths in an environment that uses
+POSIX paths.  I think you would have to use Linux tools only from within
+the Ubuntu sandbox.
+
+### Install Ubuntu Software
+
+Use `sudo apt-get install <package name>`.  As examples, this is how
+you would get GIT:
+
+    sudo apt-get install git
+
+This will get you a compiler for your host PC:
+
+    sudo apt-get install gcc
+
+This will get you an ARM compiler for your target:
+
+    sudo apt-get install gcc-arm-none-eabi
+
+**NOTE**: That is just an example.  I am not sure if apt-get will give you a
+current or usable compiler.  You should carefully select your toolchain
+for the needs of your project.
+
+You will also need to get the kconfig-frontends configuration as
+described below under *NuttX Configuration Tool*.  In order to build the
+kconfig-frontends configuration tool you will also need: `make`, `gperf`,
+`flex`, `bison`, and `libncurses-dev`.
+
+That is enough to do a basic NuttX build.
+
+### Integrating with Windows Tools
+
+If you want to integrate with Windows native tools, then you would need
+deal with the same kind of craziness as with integrating Cygwin with
+native toolchains, see the section *Cygwin Build Problems* below.
+
+However, there is currently no build support for using Windows native
+tools with Ubuntu under Windows.  This tool combination is made to work
+with Cygwin through the use of the `cygpath -w` tool that converts paths
+from say `/cydrive/c/Program Files` to `C:\Program Files`.  There is,
+however, no corresponding tool to convert `/mnt/c/Program Files` in the
+Ubuntu environment.
+
+### Graphics Support
+
+The Ubuntu version support by Microsoft is a command-line only version.
+There is no support for Linux graphics utilities.
+
+This limitation is not a limitation of Ubuntu, however, only in what
+Microsoft is willing to support.  If you install a X-Server, then you
+can also use basic graphics utilities.  See for example:
+
+  <http://www.howtogeek.com/261575/how-to-run-graphical-linux-desktop-applications-from-windows-10s-bash-shell/>
+
+Many Linux graphics programs would, however, also require a graphics
+framework like GTK or Qt.  So this might be a trip down the rabbit hole.
+
+### Using macOS
+
+You need to install at least the following tools specific to macOS.
+
+  * flock (used by APPDIR build logic)
+    
+A macOS port is available at: <https://github.com/discoteq/flock>
+  
+    brew tap discoteq/discoteq
+    brew install flock
+  
+  If you want to build the sim:
+
+  * Xcode (the native compiler and the rest of the toolchain)
+
+  * ELF toolchain (if you want to build modules for CONFIG_LIBC_MODLIB)
+
+    brew install x86_64-elf-gc
+
+# INSTALLATION
+
+There are two ways to get NuttX:  You may download released, stable
+tarballs from either the project website.  Or you may get NuttX by
+cloning the GIT repositories.  Let's consider the released tarballs
+first:
+
+## Download and Unpack
+
+Download and unpack the NuttX tarball.  If you are reading this, then
+you have probably already done that.  After unpacking, you will end
+up with a directory called nuttx-version (where version is the NuttX
+version number). You might want to rename that directory nuttx to
+match the various instructions in the documentation and some scripts
+in the source tree.
+
+  * Download location:
+  
+    <https://nuttx.apache.org/download/>
+  
+  * Legacy download locations:
+
+    <https://bitbucket.org/nuttx/nuttx/downloads>  
+    <https://sourceforge.net/projects/nuttx/files/nuttx/>
+
+## Semi-Optional apps/ Package
+
+All NuttX libraries and example code used to be in included within
+the NuttX source tree.  As of NuttX-6.0, this application code was
+moved into a separate tarball, the apps tarball.  If you are just
+beginning with NuttX, then you will want to download the versioned
+apps tarball along with the NuttX tarball.  If you already have your
+own product application directory, then you may not need the apps
+tarball.
+
+It is called "Semi-optional" because if you don't have some `apps/`
+directory, NuttX will *fail* to build! You do not necessarily need
+to use the NuttX apps tarball but may, instead, provide your own
+custom application directory.  Such a custom directory would need
+to include a valid Makefile to support the build and a valid Kconfig
+file to support the configuration.  More about these files later.
+
+Download then unpack the apps tarball in the same directory where you
+unpacked the NuttX tarball.  After you unpack the apps tarball, you
+will have a new directory called apps-version (where the version
+should exactly match the version of the NuttX tarball).  Again, you
+might want to rename the directory to simply apps/ to match what
+you read in the documentation
+
+After unpacking (and renaming) the apps tarball, you will have two
+directories side by side like this:
+
+             |
+        +----+----+
+        |         |
+      nuttx/     apps/
+
+This is important because the NuttX build will expect to find the
+apps directory in that (default) location.  That default location
+can be changed by modifying your NuttX configuration file, but that
+is another story.
+
+## Installation Directories with Spaces in the Path
+
+The nuttx build directory should reside in a path that contains no
+spaces in any higher level directory name.  For example, under
+Cygwin, your home directory might be formed from your first and last
+names like: `/home/First Last`. That will cause strange errors when
+the make system tries to build.
+
+[Actually, that problem is probably not too difficult to fix.  Some
+ Makefiles probably just need some paths within double quotes]
+
+I work around spaces in the home directory name, by creating a
+new directory that does not contain any spaces, such as `/home/nuttx`.
+Then I install NuttX in `/home/nuttx` and always build from
+`/home/nuttx/nuttx-code`.
+
+## Downloading from Repositories
+
+### Cloning the Repository
+
+**BEFORE** cloning repositories on any Windows platform do the following GIT
+command:
+
+    git config --global core.autocrlf false
+
+That will avoid conversions of linefeeds (newlines, \n) to carriage
+return plus linefeed sequences (\r\n)
+
+The current NuttX du jour is available in from a GIT repository.  Here are
+instructions for cloning the core NuttX RTOS (corresponding to the nuttx
+tarball discussed above):
+
+    git clone https://gitbox.apache.org/repos/asf/incubator-nuttx.git nuttx
+
+-or-
+
+    git clone https://github.com/apache/incubator-nuttx.git nuttx
+
+And the semi-optional apps/ application directory and be cloned like:
+
+    git clone https://gitbox.apache.org/repos/asf/incubator-nuttx-apps.git apps
+  
+-or-
+  
+    git clone https://github.com/apache/incubator-nuttx-apps.git apps
+
+That will give you the same directory structure like this:
+    
+             |
+        +----+----+
+        |         |
+      nuttx/     apps/
+
+### Configuring the Clones
+
+The following steps need to be performed for each of the repositories.
+After changing to the clone directory:
+
+Set your identity:
+
+    git config --global user.name "My Name"
+    git config --global user.email my.name@example.com
+  
+Colorized diffs are much easier to read:
+
+    git config --global color.branch auto
+    git config --global color.diff auto
+    git config --global color.interactive auto
+    git config --global color.status auto
+
+Checkout other settings
+
+    git config --list
+
+### Cloning NuttX Inside Cygwin
+
+If you are cloning the NuttX repository, it is recommended to avoid
+automatic end of lines conversions by git. These conversions may break
+some scripts like configure.sh. Before cloning, do the following:
+
+    git config --global core.autocrlf false
+
+## Related Repositories
+
+These are standalone repositories:
+
+  * <https://gitbox.apache.org/repos/asf/incubator-nuttx-apps>  
+    or  
+    <https://github.com/apache/incubator-nuttx-apps.git>
+    
+    This directory holds an optional package of applications and libraries
+    can be used with the NuttX RTOS.  There is a README.txt file there that
+    will provide more information about that package.
+
+  * <https://bitbucket.org/nuttx/nxwidgets>
+  
+    This is the NuttX C++ graphics support.  This includes NxWM, the tiny
+    NuttX Window Manager.
+
+  * <https://bitbucket.org/nuttx/uclibc>
+  
+    This repository contains a version of the uClibc++ C++ library.  This code
+    originates from <http://cxx.uclibc.org/> and has been adapted for NuttX by the
+    RGMP team (<http://rgmp.sourceforge.net/wiki/index.php/Main_Page>).
+
+  * <https://bitbucket.org/nuttx/buildroot>
+  
+    A environment that you can to use to build a custom, NuttX GNU toolchain.
+
+  * <https://bitbucket.org/nuttx/tools>
+  
+    There are snapshots of some tools here that you will need to work with
+    NuttX:  kconfig-frontends, genromfs, and others.
+
+## Notes about Header Files
+
+### Other C-Library Header Files
+
+When a GCC toolchain is built, it must be built against a C library.
+The compiler together with the contents of the C library completes the
+C language definition and provides the complete C development
+environment.  NuttX provides its own, built-in C library.  So the
+complete, consistent C language definition for use with NuttX comes from
+the combination of the compiler and the header files provided by the
+NuttX C library.
+
+When a GCC toolchain is built, it incorporates the C library header
+files into the compiler internal directories and, in this way, the C
+library really becomes a part of the toolchain.  If you use the NuttX
+buildroot toolchain as described below under "NuttX Buildroot
+Toolchain", your GCC toolchain will build against the NuttX C library
+and will incorporate the NuttX C library header files as part of the
+toolchain.
+
+If you use some other, third-party tool chain, this will not be the
+case, however.  Those toolchains were probably built against some
+other, incompatible C library distribution (such as newlib).  Those
+tools will have incorporated the incompatible C library header files
+as part of the toolchain.  These incompatible header files must *not*
+be used with NuttX because they will conflict with definitions in the
+NuttX built-in C-Library.  For such toolchains that include header
+files from a foreign C-Library, NuttX must be compiled without using
+the standard header files that are distributed with your toolchain.
+This prevents including conflicting, incompatible header files such
+as stdio.h.
+
+The math.h and stdarg.h are probably the two most trouble some header
+files to deal with.  These troublesome header files are discussed in
+more detail below.
+
+### Header Files Provided by Your Toolchain
+
+Certain header files, such as `setjmp.h`, `stdarg.h`, and `math.h`, may still
+be needed from your toolchain and your compiler may not, however, be able
+to find these if you compile NuttX without using standard header files
+(i.e., with `-nostdinc`).  If that is the case, one solution is to copy
+those header file from your toolchain into the NuttX include directory.
+
+### Duplicated Header Files
+
+There are also a few header files that can be found in the `nuttx/include`
+directory which are duplicated by the header files from your toolchain.
+stdint.h and stdbool.h are examples.  If you prefer to use the `stdint.h`
+and `stdbool.h` header files from your toolchain, those could be copied
+into the `nuttx/include/` directory. Using most other header files from
+your toolchain would probably cause errors.
+
+### math.h
+
+Even though you should not use a foreign C-Library, you may still need
+to use other, external libraries with NuttX.  In particular, you may
+need to use the math library, libm.a.  NuttX supports a generic, built-in
+math library that can be enabled using `CONFIG_LIBM=y`.  However, you may
+still want to use a higher performance external math library that has
+been tuned for your CPU.  Sometimes such tuned math libraries are
+bundled with your toolchain.
+
+The math library header file, `math.h`, is a then special case.  If you do
+nothing, the standard math.h header file that is provided with your
+toolchain will be used.
+
+If you have a custom, architecture specific math.h header file, then
+that header file should be placed at `arch/<cpu>/include/math.h`.  There
+is a stub `math.h` header file located at `include/nuttx/lib/math.h`.  This stub
+header file can be used to "redirect" the inclusion to an architecture-
+specific math.h header file.  If you add an architecture specific math.h
+header file then you should also define `CONFIG_ARCH_MATH_H=y` in your
+NuttX Configuration file.  If `CONFIG_ARCH_MATH_H` is selected, then the
+top-level Makefile will copy the stub math.h header file from
+`include/nuttx/lib/math.h` to `include/math.h` where it will become the system
+`math.h` header file.  The stub `math.h` header file does nothing other
+than to include that architecture-specific `math.h` header file as the
+system `math.h` header file.
+
+### float.h
+
+If you enable the generic, built-in math library, then that math library
+will expect your toolchain to provide the standard `float.h` header file.
+The float.h header file defines the properties of your floating point
+implementation.  It would always be best to use your toolchain's `float.h`
+header file but if none is available, a default `float.h` header file will
+be provided if this option is selected.  However, there is no assurance
+that the settings in this `float.h` are actually correct for your platform!
+
+### stdarg.h
+
+In most cases, the correct version of stdarg.h is the version provided
+with your toolchain.  However, sometimes there are issues with
+using your toolchains `stdarg.h`.  For example, it may attempt to draw in
+header files that do not exist in NuttX or perhaps the header files that
+it uses are not compatible with the NuttX header files.  In those cases,
+you can use an architecture-specific `stdarg.h` header file by defining
+`CONFIG_ARCH_STDARG_H=y`.
+
+See the discussion above for the `math.h` header.  This setting works
+exactly the same for the `stdarg.h` header file.
+
+# CONFIGURING NUTTX
+
+## Instantiating "Canned" Configurations
+
+### `configure.sh` and `configure.bat`
+
+"Canned" NuttX configuration files are retained in:
+
+    boards/<arch-name>/<chip-name>/<board-name>/configs/<config-dir>
+
+Where `<board-name>` is the name of your development board and `<config-dir>`
+is the name of the sub-directory containing a specific configuration for
+that board. `<arch-name>` and `<chip-name>` refer to characteristics of the
+MCU used on the board: `<arch-name>` is the CPU architecture implemented
+by the MCU; `<chip-name>` identifies the MCU chip family.  Only a few
+steps are required to instantiate a NuttX configuration, but to make the
+configuration even easier there are scripts available in the tools/
+sub-directory combines those simple steps into one command.
+
+There is one tool for use with any Bash-like shell that does configuration
+steps.  It is used as follows:
+
+    tools/configure.sh <board-name>:<config-dir>
+
+There is an alternative Windows batch file that can be used in the windows
+native environment like:
+
+    tools\configure.bat <board-name>:<config-dir>
+
+And, to make sure that other platforms are supported, there is also a
+C program at tools/configure.c that can be compiled to establish the
+board configuration.
+
+See `tools/README.txt` for more information about these scripts.
+
+General information about configuring NuttX can be found in:
+
+    {TOPDIR}/boards/README.txt
+    {TOPDIR}/boards/<arch-name>/<chip-name>/<board-name>/README.txt
+
+### The Hidden Configuration Scripts:
+
+As mentioned above, there are only a few simple steps to instantiating a
+NuttX configuration.  Those steps are hidden by the configuration scripts
+but are summarized below:
+  
+  1. Copy Files
+  
+     Configuring NuttX requires only copying two files from the
+     `<config-dir>` to the directory where you installed NuttX (TOPDIR):
+  
+       * Copy `boards/<arch-name>/<chip-name>/<board-name>/configs/<config-dir>/Make.def` to `{TOPDIR}/Make.defs`
+    
+         OR
+    
+       * Copy `boards/<arch-name>/<chip-name>/<board-name>/scripts/Make.def`
+         to `{TOPDIR}/Make.defs`
+    
+         Make.defs describes the rules needed by your tool chain to compile
+         and link code.  You may need to modify this file to match the
+         specific needs of your toolchain.  NOTE that a configuration may
+         have its own unique Make.defs file in its configuration directory or
+         it may use a common Make.defs file for the board in the scripts/
+         directory.  The first takes precedence.
+    
+       * Copy `boards/<arch-name>/<chip-name>/<board-name>/configs/<config-dir>/defconfig` to `{TOPDIR}/.config`
+    
+         The defconfig file holds the actual build configuration.  This
+         file is included by all other make files to determine what is
+         included in the build and what is not.  This file is also used
+         to generate a C configuration header at `include/nuttx/config.h`.
+    
+       * Copy other, environment-specific files to `{TOPDIR}`
+    
+         This might include files like .gdbinit or IDE configuration files
+         like .project or .cproject.
+  
+  2. Refresh the Configuration
+  
+     New configuration setting may be added or removed.  Existing settings
+     may also change there values or options.  This must be handled by
+     refreshing the configuration as described below.
+    
+     NOTE:  NuttX uses only compressed defconfig files.  For the NuttX
+     defconfig files, this refreshing step is *NOT* optional; it is also
+     necessary to uncompress and regenerate the full making file.  This is
+     discussed further below.
+
+## Refreshing Configurations
+
+Configurations can get out of date.  As new configuration settings are
+added or removed or as dependencies between configuration settings
+change, the contents of a default configuration can become out of synch
+with the build systems.  Hence, it is a good practice to "refresh" each
+configuration after configuring and before making.  To refresh the
+configuration, use the NuttX Configuration Tool like this:
+
+    make oldconfig
+
+AFTER you have instantiated the NuttX configuration as described above.
+The configuration step copied the .config file into place in the top-level
+NuttX directory; 'make oldconfig' step will then operate on that .config
+file to bring it up-to-date.
+
+If your configuration is out of date, you will be prompted by 'make oldconfig'
+to resolve the issues detected by the configuration tool, that is, to
+provide values for the new configuration options in the build system.  Doing
+this can save you a lot of problems down the road due to obsolete settings in
+the default board configuration file.  The NuttX configuration tool is
+discussed in more detail in the following paragraph.
+
+Confused about what the correct value for a new configuration item should
+be?  Enter ? in response to the 'make oldconfig' prompt and it will show
+you the help text that goes with the option.
+
+If you don't want to make any decisions are willing to just accept the
+recommended default value for each new configuration item, an even easier
+way is:
+
+    make olddefconfig
+
+The olddefconfig target will simply bring your configuration up to date with
+the current Kconfig files, setting any new options to the default value.
+No questions asked.
+
+## NuttX Configuration Tool
+
+An automated tool has been incorporated to support re-configuration
+of NuttX.  This tool is based on the kconfig-frontends application available
+at <https://bitbucket.org/nuttx/tools/src/master/kconfig-frontends/>.  (This
+is a snapshot of the old <http://ymorin.is-a-geek.org/projects/kconfig-frontends>
+which is no longer available.)  This application provides a tool called
+`kconfig-mconf` that is used by the NuttX top-level Makefile. The following
+make target is provided:
+
+    make menuconfig
+
+This make target will bring up NuttX configuration menus.
+
+**WARNING**:  Never do `make menuconfig` on a configuration that has
+not been converted to use the kconfig-frontends tools!  This will
+damage your configuration (see
+<http://www.nuttx.org/doku.php?id=wiki:howtos:convertconfig>).
+
+How do we tell a new configuration from an old one? See "Incompatibilities
+with Older Configurations" below.
+
+The `menuconfig` make target depends on two things:
+
+  1. The Kconfig configuration data files that appear in almost all
+     NuttX directories.  These data files are the part that is still
+     under development (patches are welcome!).  The Kconfig files
+     contain configuration information for the configuration settings
+     relevant to the directory in which the Kconfig file resides.
+     
+     NOTE: For a description of the syntax of this configuration file,
+     see kconfig-language.txt in the tools repository at
+     <https://bitbucket.org/nuttx/tools>
+  
+  2. The `kconfig-mconf` tool. `kconfig-mconf` is part of the
+     kconfig-frontends package.  You can download that package from the
+     snapshot in the tools repository at <https://bitbucket.org/nuttx/tools>.
+  
+     Building kconfig-frontends under Linux may be as simple as
+     `configure; make; make install` but there may be some build
+     complexities, especially if you are building under Cygwin.  See
+     the more detailed build instructions in the top-level README.txt
+     file of the tools repository at <https://bitbucket.org/nuttx/tools>.
+  
+  
+     The `make install` step will, by default, install the `kconfig-mconf`
+     tool at `/usr/local/bin/mconf`.  Where ever you choose to
+     install `kconfig-mconf`, make certain that your PATH variable includes
+     a path to that installation directory.
+  
+     The kconfig-frontends tools will not build in a native Windows
+     environment directly "out-of-the-box".  For the Windows native
+     case, you can use the modified version of kconfig-frontends
+     that can be found at
+
+     <http://uvc.de/posts/linux-kernel-configuration-tool-kconfig-under-windows.html>  
+
+     or a more recent port that can be found at  
+
+     <http://reclonelabs.com/more-kconfig-awesomeness-for-windows/>.
+   
+The basic configuration order is "bottom-up":
+   
+   - Select the build environment,
+   - Select the processor,
+   - Select the board,
+   - Select the supported peripherals
+   - Configure the device drivers,
+   - Configure the application options on top of this.
+   
+This is pretty straight forward for creating new configurations
+but may be less intuitive for modifying existing configurations.
+
+Another ncurses-based tool that is an option to kconfig-mconf is
+kconfig-nconf.  The differences are primary in in the aesthetics of the
+UI.  If you have kconfig-nconf built, then you can invoke that front end
+with:
+   
+     make nconfig
+   
+If you have an environment that supports the Qt or GTK graphical systems
+(probably KDE or gnome, respectively, or Cygwin under Windows with Qt or
+GTK installed), then you can also build the graphical kconfig-frontends,
+kconfig-qconf and kconfig-gconf.  In these case, you can start the
+graphical configurator with either:
+   
+     make qconfig
+   
+ or
+   
+     make gconfig
+   
+Some keyboard shortcuts supported by kconfig-mconf, the tool that runs
+when you do 'make menuconfig':
+
+   - `?` will bring up the mconfig help display.
+   
+   - `/` can be used find configuration selections.
+   
+   - `Z` can be used to reveal hidden configuration options
+   
+These last two shortcuts are described further in the following
+paragraphs.
+
+## Finding Selections in the Configuration Menus
+
+The NuttX configuration options have gotten complex and it can be very
+difficult to find options in the menu trees if you are not sure where
+to look.  The "basic configuration order" describe above can help to
+narrow things down.
+
+But if you know exactly what configuration setting you want to select,
+say CONFIG_XYZ, but not where to find it, then the 'make menuconfig'
+version of the tool offers some help:  By pressing the '/' key, the
+tool will bring up a menu that will allow you to search for a
+configuration item.  Just enter the string CONFIG_XYZ and press 'ENTER'.
+It will show you not only where to find the configuration item, but
+also all of the dependencies related to the configuration item.
+
+## Reveal Hidden Configuration Options
+
+If you type `Z`, then kconfig-mconf will change what is displayed.
+Normally, only enabled features that have all of their dependencies met
+are displayed.  That is, of course, not very useful if you would like to
+discover new options or if you are looking for an option and do not
+realize that the dependencies have not yet been selected and, hence, it
+is not displayed.
+
+But if you enter `Z`, then every option will be shown, whether or not its
+dependencies have been met.  You can then see everything that could be
+selected with the right dependency selections.  These additional options
+will be shown the `-` for the selection and for the value (since it
+cannot be selected and has no value).  About all you do is to select
+the `<Help>` option to see what the dependencies are.
+
+## Make Sure that You are on the Right Platform
+
+Saved configurations may run on Linux, Cygwin (32- or 64-bit), or other
+platforms.  The platform characteristics can be changed use `make
+menuconfig`.  Sometimes this can be confusing due to the differences
+between the platforms.  Enter sethost.sh
+
+sethost.sh is a simple script that changes a configuration to your
+host platform.  This can greatly simplify life if you use many different
+configurations.  For example, if you are running on Linux and you
+configure like this:
+
+    tools/configure.sh board:configuration
+
+The you can use the following command to both (1) make sure that the
+configuration is up to date, AND (2) the configuration is set up
+correctly for Linux:
+
+    tools/sethost.sh -l
+
+Or, if you are on a Windows/Cygwin 64-bit platform:
+
+    tools/sethost.sh -c
+
+Or, for MSYS/MSYS2:
+
+    tools/sethost.sh -g
+
+Other options are available from the help option built into the
+script.  You can see all options with:
+
+    tools/sethost.sh -h
+
+Recently, the options to the configure.sh (and configure.bat) scripts have
+been extended so that you both setup the configuration, select for the host
+platform that you use, and uncompress and refresh the defconfig file all in
+one command like:
+
+    tools/configure.sh -l board:configuration
+
+For a Linux host or for a Windows/Cygwin host:
+
+    tools/configure.sh -c board:configuration
+
+Other options are available from the help option built into the
+script.  You can see all options with:
+
+    tools/configure.sh -h
+
+## Comparing Two Configurations
+
+If you try to compare two configurations using 'diff', you will probably
+not be happy with the result.  There are superfluous things added to
+the configuration files that make comparisons with the human eye
+difficult.
+
+There is a tool at nuttx/tools/cmpconfig.c that can be built to simplify
+these comparisons.  The output from this difference tool will show only
+the meaningful differences between two configuration files.  This tool is
+built as follows:
+
+    cd nuttx/tools
+    make -f Makefile.host
+
+This will create a program called 'cmpconfig' or 'comconfig.exe' on Windows.
+
+Why would you want to compare two configuration files?  Here are a few
+of the reasons why I do this
+
+  1. When I create a new configuration I usually base it on an older
+     configuration and I want to know, "What are the options that I need to
+     change to add the new feature to the older configurations?"  For example,
+     suppose that I have a boardA/nsh configuration and I want to create a
+     boardA/nxwm configuration.  Suppose I already have boardB/nsh and
+     boardB/nxwm configurations.  Then by comparing the boardB/nsh with the
+     boardB/nxwm I can see the modifications that I would need to make to my
+     boardA/nsh to create a new  boardA/nxwm.
+  
+  2. But the most common reason that I use the 'cmpconfig' program is to
+     check the results of "refreshing" a configuration with 'make oldconfig'
+     (see the paragraph "Refreshing Configurations" above).  The 'make
+     oldconfig' command will make changes to my configuration and using
+     'cmpconfig', I can see precisely what those changes were and if any
+     should be of concern to me.
+  
+  3. The 'cmpconfig' tool can also be useful when converting older, legacy
+     manual configurations to the current configurations based on the
+     kconfig-frontends tools.  See the following paragraph.
+
+## Making defconfig Files
+
+### .config Files as defconfig Files:
+
+The minimum defconfig file is simply the generated .config file with
+CONFIG_APPS_DIR setting removed or commented out.  That setting provides
+the name and location of the apps/ directory relative to the nuttx build
+directory.  The default is ../apps/, however, the apps directory may be
+any other location and may have a different name.  For example, the name
+of versioned NuttX releases are always in the form apps-xx.yy where xx.yy
+is the version number.
+
+### Finding the apps/ Directory Path:
+
+When the default configuration is installed using one of the scripts or
+programs in the NuttX tools directory, there will be an option to provide
+the path to the apps/ directory.  If not provided, then the configure tool
+will look around and try to make a reasonable decision about where the
+apps/ directory is located.
+
+### Compressed defconfig Files:
+
+The Makefile also supports an option to generate very small defconfig
+files.  The .config files are quite large and complex.  But most of the
+settings in the .config file simply have the default settings from the
+Kconfig files.  These .config files can be converted into small defconfig
+file:
+    
+    make savedefconfig
+    
+That make target will generate a defconfig file in the top-level
+directory.  The size reduction is really quite remarkable:
+    
+    wc -l .config defconfig
+     1085 .config
+       82 defconfig
+     1167 total
+    
+In order to be usable, the .config file installed from the compressed
+defconfig file must be reconstituted using:
+    
+    make olddefconfig
+    
+  > **NOTE 1**:  Only compressed defconfig files are retained in the NuttX repository.
+  > All patches and PRs that attempt to add or modify a defconfig file MUST
+  > use the compressed defconfig format as created by 'make savdefconfig.'
+    
+  > **NOTE 2**:  When 'make savedefconfig' runs it will try several things some of
+  > which are expected to fail.  In these cases you will see an error message
+  > from make followed by "(ignored)."  You should also ignore these messages
+    
+**CAUTION**:  This size reduction was accomplished by removing all setting
+from the .config file that were at the default value.  'make olddefconfig'
+can regenerate the original .config file by simply restoring those default
+settings.  The underlying assumption here is, of course, that the default
+settings do not change.  If the default settings change, and they often
+do, then the original .config may not be reproducible.
+
+So if your project requires 100% reproducibility over a long period of
+time, you make want to save the complete .config files vs. the standard,
+compressed defconfig file.
+
+### Configuring with "Compressed" defconfig Files:
+
+As described above defconfig, all NuttX defconfig files are compressed
+using 'make savedeconfig'.  These compressed defconfig files are
+generally not fully usable as they are and may not build the target
+binaries that you want because the compression process removed all of
+the default settings from the defconfig file.  To restore the default
+settings, you should run the following after configuring:
+
+    make olddefconfig
+
+That will restore the the missing defaulted values.
+
+Using this command after configuring is generally a good practice anyway:
+Even if the defconfig files are not "compressed" in this fashion, the
+defconfig file may be old and the only way to assure that the installed
+.config is is up to date is via 'make oldconfig' or 'make olddefconfig'.
+See the paragraph above entitled ""Refreshing Configurations" for
+additional information.
+
+## Incompatibilities with Older Configurations
+
+**WARNING**
+
+The current NuttX build system supports *only* the new compressed,
+defconfig configuration files generated using the kconfig-frontends tools
+as described in the preceding section.  Support for the older, legacy,
+manual configurations was eliminated in NuttX 7.0; support for
+uncompressed .config-files-as-defconfig files was eliminated after
+NuttX-7.21.  All configurations must now be done using the
+kconfig-frontends tool.  The older manual configurations and the new
+kconfig-frontends configurations are not compatible.  Old legacy
+configurations can *not* be used with the kconfig-frontends tool and,
+hence, cannot be used with releases of NuttX 7.0 and beyond:
+
+If you run 'make menuconfig' with a legacy configuration the resulting
+configuration will probably not be functional.
+
+  > Q: How can I tell if a configuration is a new kconfig-frontends
+  >   configuration or an older, manual configuration?
+  >
+  > A: Only old, manual configurations will have an appconfig file
+  > 
+  > Q: How can I convert a older, manual configuration into a new,
+  >    kconfig-frontends toolchain.
+  >
+  > A: Refer to <http://www.nuttx.org/doku.php?id=wiki:howtos:convertconfig>
+  
+**WARNING**
+
+As described above, whenever you use a configuration, you really should
+always refresh the configuration with the following command *before* you
+make NuttX:
+
+    make oldconfig
+
+OR
+
+    make olddefconfig
+
+This will make sure that the configuration is up-to-date in the event that
+it has lapsed behind the current NuttX development (see the paragraph
+"Refreshing Configurations" above).  But this only works with *new*
+configuration files created with the kconfig-frontends tools.
+
+Further, this step is *NOT* optional with the new, compressed defconfig
+files.  It is a necessary step that will also uncompress the defconfig
+file, regenerating the .config and making it usable for NuttX builds.
+
+Never do `make oldconfig` (OR `make menuconfig`) on a  configuration that
+has not been converted to use the kconfig-frontends tools!  This will
+damage your configuration (see
+<http://www.nuttx.org/doku.php?id=wiki:howtos:convertconfig>).
+
+## NuttX Configuration Tool under DOS
+
+  Recent versions of NuttX support building NuttX from a native Windows
+  console window (see *Native Windows Build* below).  But kconfig-frontends
+  is a Linux tool.  At one time this was a problem for Windows users, but
+  now there are two specially modified versions of the kconfig-frontends
+  tools that can be used.  One can be found here:
+  <http://uvc.de/posts/linux-kernel-configuration-tool-kconfig-under-windows.html>
+
+  The configuration steps of the most recent versions of NuttX require the
+  kconfig-tweak tool that is not not available in the the above.  However,
+  there has been an update to this Kconfig Windows tools that does include
+  kconfig-tweak:  http://reclonelabs.com/more-kconfig-awesomeness-for-windows/
+
+  Source code is available here: <https://github.com/reclone/kconfig-frontends-win32>
+  and <https://github.com/reclone/kconfig-frontends-win32/releases>
+
+  It is also possible to use the version of kconfig-frontends built
+  under Cygwin outside of the Cygwin "sandbox" in a native Windows
+  environment:
+
+  1. You can run the configuration tool using Cygwin.  However, the
+     Cygwin Makefile.win will complain so to do this will, you have
+     to manually edit the .config file:
+     
+     a. Delete the line: CONFIG_WINDOWS_NATIVE=y

Review comment:
       @v01d Can you use backticks here around `CONFIG_WINDOWS_NATIVE=y`?

##########
File path: README.md
##########
@@ -0,0 +1,2513 @@
+# APACHE NUTTX (INCUBATING)
+
+* Introduction
+  - Incubation Status
+* Community
+  - Getting Help
+  - Mailing Lists
+  - Issue Tracker
+  - Source Code
+  - Website Source Code
+* Environments
+  - Installing Cygwin
+  - Ubuntu Bash under Windows 10
+  - Using macOS
+* Installation
+  - Download and Unpack
+  - Semi-Optional apps/ Package
+  - Installation Directories with Spaces in the Path
+  - Downloading from Repositories
+  - Related Repositories
+  - Notes about Header Files
+* Configuring NuttX
+  - Instantiating "Canned" Configurations
+  - Refreshing Configurations
+  - NuttX Configuration Tool
+  - Finding Selections in the Configuration Menus
+  - Reveal Hidden Configuration Options
+  - Make Sure that You are on the Right Platform
+  - Comparing Two Configurations
+  - Making defconfig Files
+  - Incompatibilities with Older Configurations
+  - NuttX Configuration Tool under DOS
+* Toolchains
+  - Cross-Development Toolchains
+  - NuttX Buildroot Toolchain
+* Shells
+* Building NuttX
+  - Building
+  - Re-building
+  - Build Targets and Options
+  - Native Windows Build
+  - Installing GNUWin32
+* Cygwin Build Problems
+  - Strange Path Problems
+  - Window Native Toolchain Issues
+* Documentation
+
+# INTRODUCTION
+
+Apache NuttX (Incubating) is a real-time operating system (RTOS) with an
+emphasis on standards compliance and small footprint.  Scalable from 8-bit
+to 32-bit microcontroller environments, the primary governing standards in
+NuttX are POSIX and ANSI standards. Additional standard APIs from Unix and
+other common RTOSs (such as VxWorks) are adopted for functionality not
+available under these standards, or for functionality that is not
+appropriate for deeply-embedded environments (such as fork()).
+
+Extensive documentation can be found on the project wiki:
+  <https://cwiki.apache.org/NUTTX/Nuttx>
+
+## Incubation Status
+
+Apache NuttX (Incubating) is an effort undergoing Incubation at The Apache
+Software Foundation (ASF), sponsored by the Incubator.  For more on our
+incubation effort, please see the file DISCLAIMER-WIP, in the same
+directory as this README.
+
+For brevity, the rest of this file will refer to it as Apache NuttX or
+simply NuttX.
+
+# COMMUNITY
+
+Every volunteer project obtains its strength from the people involved in
+it.  We invite you to participate as much or as little as you choose.
+
+We encourage you to:
+
+  - Use our project and provide feedback.
+  - Provide us with use-cases.
+  - Report bugs and submit patches.
+  - Contribute code or documentation.
+
+## Getting Help
+
+The best place to get help is the developer's mailing list.  Please see
+the following section:
+
+## Mailing Lists
+
+Get help using NuttX or contribute to the project on our mailing lists:
+
+  * <de...@nuttx.apache.org> is for people who want to contribute code to NuttX.
+    * To subscribe, send an email to <de...@nuttx.apache.org>.
+    * To unsubscribe, send an email to <de...@nuttx.apache.org>.
+    * View the archives at:
+      <https://www.mail-archive.com/dev@nuttx.apache.org/>
+
+  * <co...@nuttx.apache.org> is a read-only list that notifies subscribers
+  about commit messages and patches to NuttX.
+    * To subscribe, send an email to <co...@nuttx.apache.org>.
+    * To unsubscribe, send an email to <co...@nuttx.apache.org>.
+    * View the archives at:
+      <https://www.mail-archive.com/commits@nuttx.apache.org/>
+
+## Issue Tracker
+
+### Bug Reports:
+
+Found bug? Send an email to the dev list: <de...@nuttx.apache.org>
+
+Before submitting an issue, please:
+
+  - Verify that the bug does in fact exist. 
+  
+  - Search the mailing list archives to verify there is no existing issue
+    reporting the bug you've found.
+ 
+  - Consider tracking down the bug yourself in the NuttX source code and
+    submitting a patch along with your bug report.  This is a great time
+    saver for the NuttX developers and helps ensure the bug will be fixed
+    quickly.
+  
+### Feature Requests:
+  
+Enhancement requests for new features are also welcome. The more concrete
+and rational the request is, the greater the chance it will incorporated
+into future releases.
+
+## Source Code
+
+The project sources are in two Git repositories.  The core OS is in
+incubator-nuttx and the apps repository is in incubator-nuttx-apps.  These
+are housed in GitBox on ASF servers and also mirrored at GitHub.  These
+are kept in sync, so you can use whichever option you prefer.
+
+  - NuttX core OS repository:
+    
+    - Primary:
+      <https://gitbox.apache.org/repos/asf?p=incubator-nuttx.git>
+    
+    - GitHub Mirror:
+      <https://github.com/apache/incubator-nuttx>
+  
+  - Apps repository:
+    
+    - Primary:
+      <https://gitbox.apache.org/repos/asf?p=incubator-nuttx-apps.git>
+    
+    - GitHub Mirror:
+      <https://github.com/apache/incubator-nuttx-apps>
+
+## Website Source Code
+
+The project website sources are accessible via the website source code
+  repository which is also mirrored in GitHub:
+
+- Primary:
+  <https://gitbox.apache.org/repos/asf?p=incubator-nuttx-website.git>
+
+- GitHub Mirror:
+  <https://github.com/apache/incubator-nuttx-website>
+
+# ENVIRONMENTS
+
+  NuttX requires a POSIX development environment such as you would find under
+  Linux or macOS.  NuttX may also be installed and built on Windows system
+  if you also provide such a POSIX development environment.  Options for a
+  POSIX development environment under Windows include:
+
+  - An installation of Linux on a virtual machine (VM) in Windows.  I have
+    not been happy using a VM myself.  I have had stability problems with
+    open source VMs and commercial VMs cost more than I want to spend.
+    Sharing files with Linux running in a VM is awkward;  sharing devices
+    connected to the Windows box with Linux in a VM is, at the very least,
+    confusing;  Using Windows tools (such as Segger J-Link) with files
+    built under the Linux VM is not a possibility.
+
+  - The Cygwin environment.  Instructions for installation of Cygwin on a
+    Windows system are provided in the following paragraph, "Installing
+    Cygwin".  Cygwin is a mature, well-tested, and very convenient
+    environment.  It is especially convenient if you  need to
+    integrate with Windows tools and files.  Downsides are that the
+    installation time is very long and the compile times are slow.
+
+  - Ubuntu/Bash shell under Windows 10.  This is a new option under
+    Windows 10.  See the section "Ubuntu Bash under Windows 10" below.
+    This is an improvement over Cygwin if your concern is compile time;
+    its build performance is comparable to native Linux, certainly better
+    than the Cygwin build time.  It also installs in a tiny fraction of
+    the time as Cygwin, perhaps 20 minutes for the basic Ubuntu install
+    (vs. more than a day for the complete Cygwin install).
+  
+    There have been even more recent ports of Linux environment to
+    Windows.  I need to update this section to include some mention of
+    these alternatives.
+
+  - The MSYS environment.  MSYS derives from an older version of Cygwin
+    simplified and adapted to work more naturally in the Windows
+    environment.  See <http://www.mingw.org/wiki/MSYS> if you are
+    interested in using MSYS.  The advantages of the MSYS environment is
+    that it is better integrted with the native Windows environment and
+    lighter weight; it uses only a  minimal number of add-on POSIX-land
+    tools.
+  
+    The download link in that Wiki takes you to the SourceForge download
+    site.  The SourceForge MSYS project has been stagnant for some time.
+    The MSYS project has more recently moved to
+    <http://odsn.net/projects/sfnet_mingwbundle>.  Downloads of current .zip
+    files are available there but no instructions for the installation.
+
+  - MSYS2 appears to be a re-write of MSYS based on a newer version of
+    Cygwin.  Is it available at <https://www.msys2.org>.  A windows
+    installer is available at that site along with very good installation
+    instructions.  The download is relatively quick (at least compared to
+    Cygwin) and the 'pacman' package management tool supports supports
+    simple system updates.  For example, 'pacman -S git' will install the
+    GIT command line utilities.
+
+  - Other POSIX environments.  Check out:
+    
+    - UnxUtils: <https://sourceforge.net/projects/unxutils/>,
+      <https://en.wikipedia.org/wiki/UnxUtils>
+    - MobaXterm: <https://mobaxterm.mobatek.net/>
+    - Gow: <https://github.com/bmatzelle/gow/wiki>
+  
+    **Disclaimer**:  In principle, these should work.  However, I have never
+    used any of these environments and cannot guarantee that there is
+    not some less-than-obvious issues.
+  
+NuttX can also be installed and built on a native Windows system, but with
+some potential tool-related issues (see the discussion "Native Windows
+Build" under "Building NuttX" below).  GNUWin32 is used to provide
+compatible native windows tools.
+
+## Installing Cygwin
+
+Installing Cygwin on your Windows PC is simple, but time consuming.  See
+<http://www.cygwin.com/> for installation instructions. Basically you just
+need to download a tiny setup.exe program and it does the real, network
+installation for you.
+
+Some Cygwin installation tips:
+
+  1. Install at `C:\cygwin`
+  
+  2. Install **everything**:  "Only the minimal base packages from the
+     Cygwin distribution are installed by default. Clicking on categories
+     and packages in the setup.exe package installation screen will
+     provide you with the ability to control what is installed or updated.
+     Clicking on the "Default" field next to the "All" category will
+     provide you with the opportunity to install every Cygwin package.
+     Be advised that this will download and install hundreds of megabytes
+     to your computer."
+   
+If you use the "default" installation, you will be missing many
+of the Cygwin utilities that you will need to build NuttX.  The
+build will fail in numerous places because of missing packages.
+
+NOTE: The last time I installed **everything**, the download was
+about 5GiB.  The server I selected was also very slow so it took
+over a day to do the whole install!
+
+NOTE: You don't really have to install **everything** but I cannot
+answer the question "Then what should I install?"  I don't know
+the answer to that and so will continue to recommend installing
+**everything**.
+
+You should certainly be able to omit "Science", "Math", and
+"Publishing".  You can try omitting KDE, Gnome, GTK, and other
+graphics packages if you don't plan to use them.
+
+Perhaps a minimum set would be those packages listed below for the
+"Ubuntu Bash under Windows 10" installation?
+
+**UPDATE**:  Sergey Frolov had success with the following minimal
+Cygwin configuration:
+   
+   1. After starting the Cygwin installer, keep the recommended
+      packages that are pre-selected in the default configuration.
+   
+   2. Using the installation tools, add the following packages:
+      
+        make (GNU make)  bison        libgmp3-dev
+        gcc-core         byacc        libmpfr-dev
+        gcc-g++          gperf        libmpc-dev
+        flex             gdb          automake-1.15
+        libncurses-dev   libgmp-dev
+   
+After installing Cygwin, you will get lots of links for installed
+tools and shells.  I use the RXVT native shell.  It is fast and reliable
+and does not require you to run the Cygwin X server (which is neither
+fast nor reliable).  Unless otherwise noted, the rest of these
+instructions assume that you are at a bash command line prompt in
+either Linux or in Cygwin shell.
+
+## Using MSYS
+
+MSYS is an environment the derives from Cygwin.  Thus, most things said
+about Cygwin apply equally to MSYS.  This section will, then, focus on
+the differences when using MSYS, specifically MSYS2.
+
+Here is it assumed that you have already downloaded and installed MSYS2
+from https://www.msys2.org using the windows installer available at that
+location.  It is also assumed that you have brought in the necessary
+tools using the 'pacman' package management tool Tools needed including:
+
+  pacman -S git
+  pacman -S make
+  pacman -S gcc
+  pacman -S gdb
+
+And possibly others depending upon your usage.  Then you will need to
+build and install kconfig-frontends per the instructions of the top-level
+README.txt file in the tools repository.  This requires the following
+additional tools:
+
+    pacman -S bison
+    pacman -S gperf
+    pacman -S ncurses-devel
+    pacman -S automake-wrapper
+    pacman -S autoconf
+    pacman -S pkg-config
+
+Because of some versioning issues, I had to run 'aclocal' prior to
+running the kconfig-frontends configure script.  See "Configuring NuttX"
+below for further information.
+
+Unlike Cygwin, MSYS does not support symbolic links.  The 'ln -s' command
+will, in fact, copy a directory!  This means that you Make.defs file will
+have to include definitions like:
+
+    ifeq ($(CONFIG_WINDOWS_MSYS),y)
+      DIRLINK = $(TOPDIR)/tools/copydir.sh
+      DIRUNLINK = $(TOPDIR)/tools/unlink.sh
+    endif
+
+This will force the directory copies to work in a way that can be handled
+by the NuttX build system.  NOTE:  The default link.sh script has been
+updated so that is should now be MSYS2 compatible.  The above is preferred
+but no longer necessary in the Make.defs file.
+
+To build the simulator under MSYS, you also need:
+
+    pacman -S zlib-devel
+
+It appears that you cannot use directory names with spaces in them like
+"/c/Program\ Files \(86\)" in the MSYS path variable.  I worked around this
+by create Windows junctions like this:
+
+  1. Open the a windows command terminal,
+  
+  2. CD to `c:\msys64`, then
+  
+  3. `mklink /j programfiles "C:/Program\ Files"` and
+  
+  4. `mklink /j programfiles86 "C:/Program\ Files\ \(x86\)"`
+     
+     They then show up as `/programfiles` and `/programfiles86` with the MSYS2
+     sandbox.  Those paths can then be used with the PATH variable.  I had
+     to do something similar for the path to the GNU Tools "ARM Embedded
+     Toolchain" which also has spaces in the path name.
+
+## Ubuntu Bash under Windows 10
+
+A better version of a command-line only Ubuntu under Windows 10 (beta)
+has recently been made available from Microsoft.
+
+### Installation
+
+Installation instructions abound on the Internet complete with screen
+shots.  I will attempt to duplicate those instructions in full here.
+Here are the simplified installation steps:
+
+  - Open *Settings*.
+  
+  - Click on *Update & security*.
+  
+  - Click on *For Developers*.
+  
+  - Under *Use developer features*, select the *Developer mode* option to
+    setup the environment to install Bash.
+  
+  - A message box should pop up.  Click *Yes* to turn on developer mode.
+  
+  - After the necessary components install, you'll need to restart your
+    computer.
+    
+    Once your computer reboots:
+  
+  - Open *Control Panel*.
+  
+  - Click on *Programs*.
+  
+  - Click on *Turn Windows features on or off*.
+  
+  - A list of features will pop up, check the *Windows Subsystem for Linux
+    (beta)* option.
+  
+  - Click *OK*.
+  
+  - Once the components installed on your computer, click the *Restart
+    now* button to complete the task.
+    
+    After your computer restarts, you will notice that Bash will not appear in
+    the *Recently added* list of apps, this is because Bash isn't actually
+    installed yet. Now that you have setup the necessary components, use the
+    following steps to complete the installation of Bash:
+  
+  - Open *Start*, do a search for `bash.exe`, and press *Enter*.
+  
+  - On the command prompt, type `y` and press Enter to download and install
+    Bash from the Windows Store.  This will take awhile.
+  
+  - Then you'll need to create a default UNIX user account. This account
+    doesn't have to be the same as your Windows account. Enter the
+    username in the required field and press Enter (you can't use the
+    username `admin`).
+  
+  - Close the `bash.exe` command prompt.
+  
+  Now that you completed the installation and setup, you can open the Bash
+  tool from the Start menu like you would with any other app.
+
+### Accessing Windows Files from Ubuntu
+
+File systems will be mounted under `/mnt` so for example `C:\Program Files`
+appears at `/mnt/c/Program Files`.  This is as opposed to Cygwin where
+the same directory would appear at `/cygdrive/c/Program Files`.
+
+With these differences (perhaps a few other Windows quirks) the Ubuntu
+install works just like Ubuntu running natively on your PC.
+
+A good tip for file sharing is to use symbolic links within your Ubuntu
+home directory.  For example, suppose you have your `projects` directory
+at `C:\Documents\projects`.  Then you can set up a link to the `projects/`
+directory in your Ubuntu directory like:
+
+    ln -s /mnt/c/Documents/projects projects
+
+### Accessing Ubuntu Files From Windows
+
+In Ubuntu Userspace for Windows, the Ubuntu file system root directory is
+at:
+
+    %localappdata%\lxss\rootfs
+
+Or
+
+    C:\Users\Username\AppData\Local\lxss\rootfs
+
+However, I am unable to see my files under the rootfs\home directory.
+After some looking around, I find the home directory
+`%localappdata%\lxss\home`.
+
+With that trick access to the `/home` directory, you should actually be
+able to use Windows tools outside of the Ubuntu sandbox with versions of
+NuttX built within the sandbox using that path.
+
+### Executing Windows Tools from Ubuntu
+
+You can also execute Windows tools from within the Ubuntu sandbox:
+
+    /mnt/c/Program\ Files\ \(x86\)/Microchip/xc32/v1.43/bin/xc32-gcc.exe --version
+    Unable to translate current working directory. Using C:\WINDOWS\System32
+    xc32-gcc.exe (Microchip Technology) 4.8.3 MPLAB XC32 Compiler v1.43 Build date: Mar  1 2017
+    ...
+
+The error message indicates that there are more issues:  You cannot mix
+Windows tools that use Windows style paths in an environment that uses
+POSIX paths.  I think you would have to use Linux tools only from within
+the Ubuntu sandbox.
+
+### Install Ubuntu Software
+
+Use `sudo apt-get install <package name>`.  As examples, this is how
+you would get GIT:
+
+    sudo apt-get install git
+
+This will get you a compiler for your host PC:
+
+    sudo apt-get install gcc
+
+This will get you an ARM compiler for your target:
+
+    sudo apt-get install gcc-arm-none-eabi
+
+**NOTE**: That is just an example.  I am not sure if apt-get will give you a
+current or usable compiler.  You should carefully select your toolchain
+for the needs of your project.
+
+You will also need to get the kconfig-frontends configuration as
+described below under *NuttX Configuration Tool*.  In order to build the
+kconfig-frontends configuration tool you will also need: `make`, `gperf`,
+`flex`, `bison`, and `libncurses-dev`.
+
+That is enough to do a basic NuttX build.
+
+### Integrating with Windows Tools
+
+If you want to integrate with Windows native tools, then you would need
+deal with the same kind of craziness as with integrating Cygwin with
+native toolchains, see the section *Cygwin Build Problems* below.
+
+However, there is currently no build support for using Windows native
+tools with Ubuntu under Windows.  This tool combination is made to work
+with Cygwin through the use of the `cygpath -w` tool that converts paths
+from say `/cydrive/c/Program Files` to `C:\Program Files`.  There is,
+however, no corresponding tool to convert `/mnt/c/Program Files` in the
+Ubuntu environment.
+
+### Graphics Support
+
+The Ubuntu version support by Microsoft is a command-line only version.
+There is no support for Linux graphics utilities.
+
+This limitation is not a limitation of Ubuntu, however, only in what
+Microsoft is willing to support.  If you install a X-Server, then you
+can also use basic graphics utilities.  See for example:
+
+  <http://www.howtogeek.com/261575/how-to-run-graphical-linux-desktop-applications-from-windows-10s-bash-shell/>
+
+Many Linux graphics programs would, however, also require a graphics
+framework like GTK or Qt.  So this might be a trip down the rabbit hole.
+
+### Using macOS
+
+You need to install at least the following tools specific to macOS.
+
+  * flock (used by APPDIR build logic)
+    
+A macOS port is available at: <https://github.com/discoteq/flock>
+  
+    brew tap discoteq/discoteq
+    brew install flock
+  
+  If you want to build the sim:
+
+  * Xcode (the native compiler and the rest of the toolchain)
+
+  * ELF toolchain (if you want to build modules for CONFIG_LIBC_MODLIB)
+
+    brew install x86_64-elf-gc
+
+# INSTALLATION
+
+There are two ways to get NuttX:  You may download released, stable
+tarballs from either the project website.  Or you may get NuttX by
+cloning the GIT repositories.  Let's consider the released tarballs
+first:
+
+## Download and Unpack
+
+Download and unpack the NuttX tarball.  If you are reading this, then
+you have probably already done that.  After unpacking, you will end
+up with a directory called nuttx-version (where version is the NuttX
+version number). You might want to rename that directory nuttx to
+match the various instructions in the documentation and some scripts
+in the source tree.
+
+  * Download location:
+  
+    <https://nuttx.apache.org/download/>
+  
+  * Legacy download locations:
+
+    <https://bitbucket.org/nuttx/nuttx/downloads>  
+    <https://sourceforge.net/projects/nuttx/files/nuttx/>
+
+## Semi-Optional apps/ Package
+
+All NuttX libraries and example code used to be in included within
+the NuttX source tree.  As of NuttX-6.0, this application code was
+moved into a separate tarball, the apps tarball.  If you are just
+beginning with NuttX, then you will want to download the versioned
+apps tarball along with the NuttX tarball.  If you already have your
+own product application directory, then you may not need the apps
+tarball.
+
+It is called "Semi-optional" because if you don't have some `apps/`
+directory, NuttX will *fail* to build! You do not necessarily need
+to use the NuttX apps tarball but may, instead, provide your own
+custom application directory.  Such a custom directory would need
+to include a valid Makefile to support the build and a valid Kconfig
+file to support the configuration.  More about these files later.
+
+Download then unpack the apps tarball in the same directory where you
+unpacked the NuttX tarball.  After you unpack the apps tarball, you
+will have a new directory called apps-version (where the version
+should exactly match the version of the NuttX tarball).  Again, you
+might want to rename the directory to simply apps/ to match what
+you read in the documentation
+
+After unpacking (and renaming) the apps tarball, you will have two
+directories side by side like this:
+
+             |
+        +----+----+
+        |         |
+      nuttx/     apps/
+
+This is important because the NuttX build will expect to find the
+apps directory in that (default) location.  That default location
+can be changed by modifying your NuttX configuration file, but that
+is another story.
+
+## Installation Directories with Spaces in the Path
+
+The nuttx build directory should reside in a path that contains no
+spaces in any higher level directory name.  For example, under
+Cygwin, your home directory might be formed from your first and last
+names like: `/home/First Last`. That will cause strange errors when
+the make system tries to build.
+
+[Actually, that problem is probably not too difficult to fix.  Some
+ Makefiles probably just need some paths within double quotes]
+
+I work around spaces in the home directory name, by creating a
+new directory that does not contain any spaces, such as `/home/nuttx`.
+Then I install NuttX in `/home/nuttx` and always build from
+`/home/nuttx/nuttx-code`.
+
+## Downloading from Repositories
+
+### Cloning the Repository
+
+**BEFORE** cloning repositories on any Windows platform do the following GIT
+command:
+
+    git config --global core.autocrlf false
+
+That will avoid conversions of linefeeds (newlines, \n) to carriage
+return plus linefeed sequences (\r\n)
+
+The current NuttX du jour is available in from a GIT repository.  Here are
+instructions for cloning the core NuttX RTOS (corresponding to the nuttx
+tarball discussed above):
+
+    git clone https://gitbox.apache.org/repos/asf/incubator-nuttx.git nuttx
+
+-or-
+
+    git clone https://github.com/apache/incubator-nuttx.git nuttx
+
+And the semi-optional apps/ application directory and be cloned like:
+
+    git clone https://gitbox.apache.org/repos/asf/incubator-nuttx-apps.git apps
+  
+-or-
+  
+    git clone https://github.com/apache/incubator-nuttx-apps.git apps
+
+That will give you the same directory structure like this:
+    
+             |
+        +----+----+
+        |         |
+      nuttx/     apps/
+
+### Configuring the Clones
+
+The following steps need to be performed for each of the repositories.
+After changing to the clone directory:
+
+Set your identity:
+
+    git config --global user.name "My Name"
+    git config --global user.email my.name@example.com
+  
+Colorized diffs are much easier to read:
+
+    git config --global color.branch auto
+    git config --global color.diff auto
+    git config --global color.interactive auto
+    git config --global color.status auto
+
+Checkout other settings
+
+    git config --list
+
+### Cloning NuttX Inside Cygwin
+
+If you are cloning the NuttX repository, it is recommended to avoid
+automatic end of lines conversions by git. These conversions may break
+some scripts like configure.sh. Before cloning, do the following:
+
+    git config --global core.autocrlf false
+
+## Related Repositories
+
+These are standalone repositories:
+
+  * <https://gitbox.apache.org/repos/asf/incubator-nuttx-apps>  
+    or  
+    <https://github.com/apache/incubator-nuttx-apps.git>
+    
+    This directory holds an optional package of applications and libraries
+    can be used with the NuttX RTOS.  There is a README.txt file there that
+    will provide more information about that package.
+
+  * <https://bitbucket.org/nuttx/nxwidgets>
+  
+    This is the NuttX C++ graphics support.  This includes NxWM, the tiny
+    NuttX Window Manager.
+
+  * <https://bitbucket.org/nuttx/uclibc>
+  
+    This repository contains a version of the uClibc++ C++ library.  This code
+    originates from <http://cxx.uclibc.org/> and has been adapted for NuttX by the
+    RGMP team (<http://rgmp.sourceforge.net/wiki/index.php/Main_Page>).
+
+  * <https://bitbucket.org/nuttx/buildroot>
+  
+    A environment that you can to use to build a custom, NuttX GNU toolchain.
+
+  * <https://bitbucket.org/nuttx/tools>
+  
+    There are snapshots of some tools here that you will need to work with
+    NuttX:  kconfig-frontends, genromfs, and others.
+
+## Notes about Header Files
+
+### Other C-Library Header Files
+
+When a GCC toolchain is built, it must be built against a C library.
+The compiler together with the contents of the C library completes the
+C language definition and provides the complete C development
+environment.  NuttX provides its own, built-in C library.  So the
+complete, consistent C language definition for use with NuttX comes from
+the combination of the compiler and the header files provided by the
+NuttX C library.
+
+When a GCC toolchain is built, it incorporates the C library header
+files into the compiler internal directories and, in this way, the C
+library really becomes a part of the toolchain.  If you use the NuttX
+buildroot toolchain as described below under "NuttX Buildroot
+Toolchain", your GCC toolchain will build against the NuttX C library
+and will incorporate the NuttX C library header files as part of the
+toolchain.
+
+If you use some other, third-party tool chain, this will not be the
+case, however.  Those toolchains were probably built against some
+other, incompatible C library distribution (such as newlib).  Those
+tools will have incorporated the incompatible C library header files
+as part of the toolchain.  These incompatible header files must *not*
+be used with NuttX because they will conflict with definitions in the
+NuttX built-in C-Library.  For such toolchains that include header
+files from a foreign C-Library, NuttX must be compiled without using
+the standard header files that are distributed with your toolchain.
+This prevents including conflicting, incompatible header files such
+as stdio.h.
+
+The math.h and stdarg.h are probably the two most trouble some header
+files to deal with.  These troublesome header files are discussed in
+more detail below.
+
+### Header Files Provided by Your Toolchain
+
+Certain header files, such as `setjmp.h`, `stdarg.h`, and `math.h`, may still
+be needed from your toolchain and your compiler may not, however, be able
+to find these if you compile NuttX without using standard header files
+(i.e., with `-nostdinc`).  If that is the case, one solution is to copy
+those header file from your toolchain into the NuttX include directory.
+
+### Duplicated Header Files
+
+There are also a few header files that can be found in the `nuttx/include`
+directory which are duplicated by the header files from your toolchain.
+stdint.h and stdbool.h are examples.  If you prefer to use the `stdint.h`
+and `stdbool.h` header files from your toolchain, those could be copied
+into the `nuttx/include/` directory. Using most other header files from
+your toolchain would probably cause errors.
+
+### math.h
+
+Even though you should not use a foreign C-Library, you may still need
+to use other, external libraries with NuttX.  In particular, you may
+need to use the math library, libm.a.  NuttX supports a generic, built-in
+math library that can be enabled using `CONFIG_LIBM=y`.  However, you may
+still want to use a higher performance external math library that has
+been tuned for your CPU.  Sometimes such tuned math libraries are
+bundled with your toolchain.
+
+The math library header file, `math.h`, is a then special case.  If you do
+nothing, the standard math.h header file that is provided with your
+toolchain will be used.
+
+If you have a custom, architecture specific math.h header file, then
+that header file should be placed at `arch/<cpu>/include/math.h`.  There
+is a stub `math.h` header file located at `include/nuttx/lib/math.h`.  This stub
+header file can be used to "redirect" the inclusion to an architecture-
+specific math.h header file.  If you add an architecture specific math.h
+header file then you should also define `CONFIG_ARCH_MATH_H=y` in your
+NuttX Configuration file.  If `CONFIG_ARCH_MATH_H` is selected, then the
+top-level Makefile will copy the stub math.h header file from
+`include/nuttx/lib/math.h` to `include/math.h` where it will become the system
+`math.h` header file.  The stub `math.h` header file does nothing other
+than to include that architecture-specific `math.h` header file as the
+system `math.h` header file.
+
+### float.h
+
+If you enable the generic, built-in math library, then that math library
+will expect your toolchain to provide the standard `float.h` header file.
+The float.h header file defines the properties of your floating point
+implementation.  It would always be best to use your toolchain's `float.h`
+header file but if none is available, a default `float.h` header file will
+be provided if this option is selected.  However, there is no assurance
+that the settings in this `float.h` are actually correct for your platform!
+
+### stdarg.h
+
+In most cases, the correct version of stdarg.h is the version provided
+with your toolchain.  However, sometimes there are issues with
+using your toolchains `stdarg.h`.  For example, it may attempt to draw in
+header files that do not exist in NuttX or perhaps the header files that
+it uses are not compatible with the NuttX header files.  In those cases,
+you can use an architecture-specific `stdarg.h` header file by defining
+`CONFIG_ARCH_STDARG_H=y`.
+
+See the discussion above for the `math.h` header.  This setting works
+exactly the same for the `stdarg.h` header file.
+
+# CONFIGURING NUTTX
+
+## Instantiating "Canned" Configurations
+
+### `configure.sh` and `configure.bat`
+
+"Canned" NuttX configuration files are retained in:
+
+    boards/<arch-name>/<chip-name>/<board-name>/configs/<config-dir>
+
+Where `<board-name>` is the name of your development board and `<config-dir>`
+is the name of the sub-directory containing a specific configuration for
+that board. `<arch-name>` and `<chip-name>` refer to characteristics of the
+MCU used on the board: `<arch-name>` is the CPU architecture implemented
+by the MCU; `<chip-name>` identifies the MCU chip family.  Only a few
+steps are required to instantiate a NuttX configuration, but to make the
+configuration even easier there are scripts available in the tools/
+sub-directory combines those simple steps into one command.
+
+There is one tool for use with any Bash-like shell that does configuration
+steps.  It is used as follows:
+
+    tools/configure.sh <board-name>:<config-dir>
+
+There is an alternative Windows batch file that can be used in the windows
+native environment like:
+
+    tools\configure.bat <board-name>:<config-dir>
+
+And, to make sure that other platforms are supported, there is also a
+C program at tools/configure.c that can be compiled to establish the
+board configuration.
+
+See `tools/README.txt` for more information about these scripts.
+
+General information about configuring NuttX can be found in:
+
+    {TOPDIR}/boards/README.txt
+    {TOPDIR}/boards/<arch-name>/<chip-name>/<board-name>/README.txt
+
+### The Hidden Configuration Scripts:
+
+As mentioned above, there are only a few simple steps to instantiating a
+NuttX configuration.  Those steps are hidden by the configuration scripts
+but are summarized below:
+  
+  1. Copy Files
+  
+     Configuring NuttX requires only copying two files from the
+     `<config-dir>` to the directory where you installed NuttX (TOPDIR):
+  
+       * Copy `boards/<arch-name>/<chip-name>/<board-name>/configs/<config-dir>/Make.def` to `{TOPDIR}/Make.defs`
+    
+         OR
+    
+       * Copy `boards/<arch-name>/<chip-name>/<board-name>/scripts/Make.def`
+         to `{TOPDIR}/Make.defs`
+    
+         Make.defs describes the rules needed by your tool chain to compile
+         and link code.  You may need to modify this file to match the
+         specific needs of your toolchain.  NOTE that a configuration may
+         have its own unique Make.defs file in its configuration directory or
+         it may use a common Make.defs file for the board in the scripts/
+         directory.  The first takes precedence.
+    
+       * Copy `boards/<arch-name>/<chip-name>/<board-name>/configs/<config-dir>/defconfig` to `{TOPDIR}/.config`
+    
+         The defconfig file holds the actual build configuration.  This
+         file is included by all other make files to determine what is
+         included in the build and what is not.  This file is also used
+         to generate a C configuration header at `include/nuttx/config.h`.
+    
+       * Copy other, environment-specific files to `{TOPDIR}`
+    
+         This might include files like .gdbinit or IDE configuration files
+         like .project or .cproject.
+  
+  2. Refresh the Configuration
+  
+     New configuration setting may be added or removed.  Existing settings
+     may also change there values or options.  This must be handled by
+     refreshing the configuration as described below.
+    
+     NOTE:  NuttX uses only compressed defconfig files.  For the NuttX
+     defconfig files, this refreshing step is *NOT* optional; it is also
+     necessary to uncompress and regenerate the full making file.  This is
+     discussed further below.
+
+## Refreshing Configurations
+
+Configurations can get out of date.  As new configuration settings are
+added or removed or as dependencies between configuration settings
+change, the contents of a default configuration can become out of synch
+with the build systems.  Hence, it is a good practice to "refresh" each
+configuration after configuring and before making.  To refresh the
+configuration, use the NuttX Configuration Tool like this:
+
+    make oldconfig
+
+AFTER you have instantiated the NuttX configuration as described above.
+The configuration step copied the .config file into place in the top-level
+NuttX directory; 'make oldconfig' step will then operate on that .config
+file to bring it up-to-date.
+
+If your configuration is out of date, you will be prompted by 'make oldconfig'
+to resolve the issues detected by the configuration tool, that is, to
+provide values for the new configuration options in the build system.  Doing
+this can save you a lot of problems down the road due to obsolete settings in
+the default board configuration file.  The NuttX configuration tool is
+discussed in more detail in the following paragraph.
+
+Confused about what the correct value for a new configuration item should
+be?  Enter ? in response to the 'make oldconfig' prompt and it will show
+you the help text that goes with the option.
+
+If you don't want to make any decisions are willing to just accept the
+recommended default value for each new configuration item, an even easier
+way is:
+
+    make olddefconfig
+
+The olddefconfig target will simply bring your configuration up to date with
+the current Kconfig files, setting any new options to the default value.
+No questions asked.
+
+## NuttX Configuration Tool
+
+An automated tool has been incorporated to support re-configuration
+of NuttX.  This tool is based on the kconfig-frontends application available
+at <https://bitbucket.org/nuttx/tools/src/master/kconfig-frontends/>.  (This
+is a snapshot of the old <http://ymorin.is-a-geek.org/projects/kconfig-frontends>
+which is no longer available.)  This application provides a tool called
+`kconfig-mconf` that is used by the NuttX top-level Makefile. The following
+make target is provided:
+
+    make menuconfig
+
+This make target will bring up NuttX configuration menus.
+
+**WARNING**:  Never do `make menuconfig` on a configuration that has
+not been converted to use the kconfig-frontends tools!  This will
+damage your configuration (see
+<http://www.nuttx.org/doku.php?id=wiki:howtos:convertconfig>).
+
+How do we tell a new configuration from an old one? See "Incompatibilities
+with Older Configurations" below.
+
+The `menuconfig` make target depends on two things:
+
+  1. The Kconfig configuration data files that appear in almost all
+     NuttX directories.  These data files are the part that is still
+     under development (patches are welcome!).  The Kconfig files
+     contain configuration information for the configuration settings
+     relevant to the directory in which the Kconfig file resides.
+     
+     NOTE: For a description of the syntax of this configuration file,
+     see kconfig-language.txt in the tools repository at
+     <https://bitbucket.org/nuttx/tools>
+  
+  2. The `kconfig-mconf` tool. `kconfig-mconf` is part of the
+     kconfig-frontends package.  You can download that package from the
+     snapshot in the tools repository at <https://bitbucket.org/nuttx/tools>.
+  
+     Building kconfig-frontends under Linux may be as simple as
+     `configure; make; make install` but there may be some build
+     complexities, especially if you are building under Cygwin.  See
+     the more detailed build instructions in the top-level README.txt
+     file of the tools repository at <https://bitbucket.org/nuttx/tools>.
+  
+  
+     The `make install` step will, by default, install the `kconfig-mconf`
+     tool at `/usr/local/bin/mconf`.  Where ever you choose to
+     install `kconfig-mconf`, make certain that your PATH variable includes
+     a path to that installation directory.
+  
+     The kconfig-frontends tools will not build in a native Windows
+     environment directly "out-of-the-box".  For the Windows native
+     case, you can use the modified version of kconfig-frontends
+     that can be found at
+
+     <http://uvc.de/posts/linux-kernel-configuration-tool-kconfig-under-windows.html>  
+
+     or a more recent port that can be found at  
+
+     <http://reclonelabs.com/more-kconfig-awesomeness-for-windows/>.
+   
+The basic configuration order is "bottom-up":
+   
+   - Select the build environment,
+   - Select the processor,
+   - Select the board,
+   - Select the supported peripherals
+   - Configure the device drivers,
+   - Configure the application options on top of this.
+   
+This is pretty straight forward for creating new configurations
+but may be less intuitive for modifying existing configurations.
+
+Another ncurses-based tool that is an option to kconfig-mconf is
+kconfig-nconf.  The differences are primary in in the aesthetics of the
+UI.  If you have kconfig-nconf built, then you can invoke that front end
+with:
+   
+     make nconfig
+   
+If you have an environment that supports the Qt or GTK graphical systems
+(probably KDE or gnome, respectively, or Cygwin under Windows with Qt or
+GTK installed), then you can also build the graphical kconfig-frontends,
+kconfig-qconf and kconfig-gconf.  In these case, you can start the
+graphical configurator with either:
+   
+     make qconfig
+   
+ or
+   
+     make gconfig
+   
+Some keyboard shortcuts supported by kconfig-mconf, the tool that runs
+when you do 'make menuconfig':
+
+   - `?` will bring up the mconfig help display.
+   
+   - `/` can be used find configuration selections.
+   
+   - `Z` can be used to reveal hidden configuration options
+   
+These last two shortcuts are described further in the following
+paragraphs.
+
+## Finding Selections in the Configuration Menus
+
+The NuttX configuration options have gotten complex and it can be very
+difficult to find options in the menu trees if you are not sure where
+to look.  The "basic configuration order" describe above can help to
+narrow things down.
+
+But if you know exactly what configuration setting you want to select,
+say CONFIG_XYZ, but not where to find it, then the 'make menuconfig'
+version of the tool offers some help:  By pressing the '/' key, the
+tool will bring up a menu that will allow you to search for a
+configuration item.  Just enter the string CONFIG_XYZ and press 'ENTER'.
+It will show you not only where to find the configuration item, but
+also all of the dependencies related to the configuration item.
+
+## Reveal Hidden Configuration Options
+
+If you type `Z`, then kconfig-mconf will change what is displayed.
+Normally, only enabled features that have all of their dependencies met
+are displayed.  That is, of course, not very useful if you would like to
+discover new options or if you are looking for an option and do not
+realize that the dependencies have not yet been selected and, hence, it
+is not displayed.
+
+But if you enter `Z`, then every option will be shown, whether or not its
+dependencies have been met.  You can then see everything that could be
+selected with the right dependency selections.  These additional options
+will be shown the `-` for the selection and for the value (since it
+cannot be selected and has no value).  About all you do is to select
+the `<Help>` option to see what the dependencies are.
+
+## Make Sure that You are on the Right Platform
+
+Saved configurations may run on Linux, Cygwin (32- or 64-bit), or other
+platforms.  The platform characteristics can be changed use `make
+menuconfig`.  Sometimes this can be confusing due to the differences
+between the platforms.  Enter sethost.sh
+
+sethost.sh is a simple script that changes a configuration to your
+host platform.  This can greatly simplify life if you use many different
+configurations.  For example, if you are running on Linux and you
+configure like this:
+
+    tools/configure.sh board:configuration
+
+The you can use the following command to both (1) make sure that the
+configuration is up to date, AND (2) the configuration is set up
+correctly for Linux:
+
+    tools/sethost.sh -l
+
+Or, if you are on a Windows/Cygwin 64-bit platform:
+
+    tools/sethost.sh -c
+
+Or, for MSYS/MSYS2:
+
+    tools/sethost.sh -g
+
+Other options are available from the help option built into the
+script.  You can see all options with:
+
+    tools/sethost.sh -h
+
+Recently, the options to the configure.sh (and configure.bat) scripts have
+been extended so that you both setup the configuration, select for the host
+platform that you use, and uncompress and refresh the defconfig file all in
+one command like:
+
+    tools/configure.sh -l board:configuration
+
+For a Linux host or for a Windows/Cygwin host:
+
+    tools/configure.sh -c board:configuration
+
+Other options are available from the help option built into the
+script.  You can see all options with:
+
+    tools/configure.sh -h
+
+## Comparing Two Configurations
+
+If you try to compare two configurations using 'diff', you will probably
+not be happy with the result.  There are superfluous things added to
+the configuration files that make comparisons with the human eye
+difficult.
+
+There is a tool at nuttx/tools/cmpconfig.c that can be built to simplify
+these comparisons.  The output from this difference tool will show only
+the meaningful differences between two configuration files.  This tool is
+built as follows:
+
+    cd nuttx/tools
+    make -f Makefile.host
+
+This will create a program called 'cmpconfig' or 'comconfig.exe' on Windows.
+
+Why would you want to compare two configuration files?  Here are a few
+of the reasons why I do this
+
+  1. When I create a new configuration I usually base it on an older
+     configuration and I want to know, "What are the options that I need to
+     change to add the new feature to the older configurations?"  For example,
+     suppose that I have a boardA/nsh configuration and I want to create a
+     boardA/nxwm configuration.  Suppose I already have boardB/nsh and
+     boardB/nxwm configurations.  Then by comparing the boardB/nsh with the
+     boardB/nxwm I can see the modifications that I would need to make to my
+     boardA/nsh to create a new  boardA/nxwm.
+  
+  2. But the most common reason that I use the 'cmpconfig' program is to
+     check the results of "refreshing" a configuration with 'make oldconfig'
+     (see the paragraph "Refreshing Configurations" above).  The 'make
+     oldconfig' command will make changes to my configuration and using
+     'cmpconfig', I can see precisely what those changes were and if any
+     should be of concern to me.
+  
+  3. The 'cmpconfig' tool can also be useful when converting older, legacy
+     manual configurations to the current configurations based on the
+     kconfig-frontends tools.  See the following paragraph.
+
+## Making defconfig Files
+
+### .config Files as defconfig Files:
+
+The minimum defconfig file is simply the generated .config file with
+CONFIG_APPS_DIR setting removed or commented out.  That setting provides
+the name and location of the apps/ directory relative to the nuttx build
+directory.  The default is ../apps/, however, the apps directory may be
+any other location and may have a different name.  For example, the name
+of versioned NuttX releases are always in the form apps-xx.yy where xx.yy
+is the version number.
+
+### Finding the apps/ Directory Path:
+
+When the default configuration is installed using one of the scripts or
+programs in the NuttX tools directory, there will be an option to provide
+the path to the apps/ directory.  If not provided, then the configure tool
+will look around and try to make a reasonable decision about where the
+apps/ directory is located.
+
+### Compressed defconfig Files:
+
+The Makefile also supports an option to generate very small defconfig
+files.  The .config files are quite large and complex.  But most of the
+settings in the .config file simply have the default settings from the
+Kconfig files.  These .config files can be converted into small defconfig
+file:
+    
+    make savedefconfig
+    
+That make target will generate a defconfig file in the top-level
+directory.  The size reduction is really quite remarkable:
+    
+    wc -l .config defconfig
+     1085 .config
+       82 defconfig
+     1167 total
+    
+In order to be usable, the .config file installed from the compressed
+defconfig file must be reconstituted using:
+    
+    make olddefconfig
+    
+  > **NOTE 1**:  Only compressed defconfig files are retained in the NuttX repository.
+  > All patches and PRs that attempt to add or modify a defconfig file MUST
+  > use the compressed defconfig format as created by 'make savdefconfig.'
+    
+  > **NOTE 2**:  When 'make savedefconfig' runs it will try several things some of
+  > which are expected to fail.  In these cases you will see an error message
+  > from make followed by "(ignored)."  You should also ignore these messages
+    
+**CAUTION**:  This size reduction was accomplished by removing all setting
+from the .config file that were at the default value.  'make olddefconfig'
+can regenerate the original .config file by simply restoring those default
+settings.  The underlying assumption here is, of course, that the default
+settings do not change.  If the default settings change, and they often
+do, then the original .config may not be reproducible.
+
+So if your project requires 100% reproducibility over a long period of
+time, you make want to save the complete .config files vs. the standard,
+compressed defconfig file.
+
+### Configuring with "Compressed" defconfig Files:
+
+As described above defconfig, all NuttX defconfig files are compressed
+using 'make savedeconfig'.  These compressed defconfig files are
+generally not fully usable as they are and may not build the target
+binaries that you want because the compression process removed all of
+the default settings from the defconfig file.  To restore the default
+settings, you should run the following after configuring:
+
+    make olddefconfig
+
+That will restore the the missing defaulted values.
+
+Using this command after configuring is generally a good practice anyway:
+Even if the defconfig files are not "compressed" in this fashion, the
+defconfig file may be old and the only way to assure that the installed
+.config is is up to date is via 'make oldconfig' or 'make olddefconfig'.
+See the paragraph above entitled ""Refreshing Configurations" for
+additional information.
+
+## Incompatibilities with Older Configurations
+
+**WARNING**
+
+The current NuttX build system supports *only* the new compressed,
+defconfig configuration files generated using the kconfig-frontends tools
+as described in the preceding section.  Support for the older, legacy,
+manual configurations was eliminated in NuttX 7.0; support for
+uncompressed .config-files-as-defconfig files was eliminated after
+NuttX-7.21.  All configurations must now be done using the
+kconfig-frontends tool.  The older manual configurations and the new
+kconfig-frontends configurations are not compatible.  Old legacy
+configurations can *not* be used with the kconfig-frontends tool and,
+hence, cannot be used with releases of NuttX 7.0 and beyond:
+
+If you run 'make menuconfig' with a legacy configuration the resulting
+configuration will probably not be functional.
+
+  > Q: How can I tell if a configuration is a new kconfig-frontends
+  >   configuration or an older, manual configuration?
+  >
+  > A: Only old, manual configurations will have an appconfig file
+  > 
+  > Q: How can I convert a older, manual configuration into a new,
+  >    kconfig-frontends toolchain.
+  >
+  > A: Refer to <http://www.nuttx.org/doku.php?id=wiki:howtos:convertconfig>
+  
+**WARNING**
+
+As described above, whenever you use a configuration, you really should
+always refresh the configuration with the following command *before* you
+make NuttX:
+
+    make oldconfig
+
+OR
+
+    make olddefconfig
+
+This will make sure that the configuration is up-to-date in the event that
+it has lapsed behind the current NuttX development (see the paragraph
+"Refreshing Configurations" above).  But this only works with *new*
+configuration files created with the kconfig-frontends tools.
+
+Further, this step is *NOT* optional with the new, compressed defconfig
+files.  It is a necessary step that will also uncompress the defconfig
+file, regenerating the .config and making it usable for NuttX builds.
+
+Never do `make oldconfig` (OR `make menuconfig`) on a  configuration that
+has not been converted to use the kconfig-frontends tools!  This will
+damage your configuration (see
+<http://www.nuttx.org/doku.php?id=wiki:howtos:convertconfig>).
+
+## NuttX Configuration Tool under DOS
+
+  Recent versions of NuttX support building NuttX from a native Windows
+  console window (see *Native Windows Build* below).  But kconfig-frontends
+  is a Linux tool.  At one time this was a problem for Windows users, but
+  now there are two specially modified versions of the kconfig-frontends
+  tools that can be used.  One can be found here:
+  <http://uvc.de/posts/linux-kernel-configuration-tool-kconfig-under-windows.html>
+
+  The configuration steps of the most recent versions of NuttX require the
+  kconfig-tweak tool that is not not available in the the above.  However,
+  there has been an update to this Kconfig Windows tools that does include
+  kconfig-tweak:  http://reclonelabs.com/more-kconfig-awesomeness-for-windows/
+
+  Source code is available here: <https://github.com/reclone/kconfig-frontends-win32>
+  and <https://github.com/reclone/kconfig-frontends-win32/releases>
+
+  It is also possible to use the version of kconfig-frontends built
+  under Cygwin outside of the Cygwin "sandbox" in a native Windows
+  environment:
+
+  1. You can run the configuration tool using Cygwin.  However, the
+     Cygwin Makefile.win will complain so to do this will, you have
+     to manually edit the .config file:
+     
+     a. Delete the line: CONFIG_WINDOWS_NATIVE=y
+     
+     b. Change the apps/ directory path, CONFIG_APPS_DIR to use Unix

Review comment:
       @v01d backticks around `CONFIG_APPS_DIR`?

##########
File path: README.md
##########
@@ -0,0 +1,2513 @@
+# APACHE NUTTX (INCUBATING)
+
+* Introduction
+  - Incubation Status
+* Community
+  - Getting Help
+  - Mailing Lists
+  - Issue Tracker
+  - Source Code
+  - Website Source Code
+* Environments
+  - Installing Cygwin
+  - Ubuntu Bash under Windows 10
+  - Using macOS
+* Installation
+  - Download and Unpack
+  - Semi-Optional apps/ Package
+  - Installation Directories with Spaces in the Path
+  - Downloading from Repositories
+  - Related Repositories
+  - Notes about Header Files
+* Configuring NuttX
+  - Instantiating "Canned" Configurations
+  - Refreshing Configurations
+  - NuttX Configuration Tool
+  - Finding Selections in the Configuration Menus
+  - Reveal Hidden Configuration Options
+  - Make Sure that You are on the Right Platform
+  - Comparing Two Configurations
+  - Making defconfig Files
+  - Incompatibilities with Older Configurations
+  - NuttX Configuration Tool under DOS
+* Toolchains
+  - Cross-Development Toolchains
+  - NuttX Buildroot Toolchain
+* Shells
+* Building NuttX
+  - Building
+  - Re-building
+  - Build Targets and Options
+  - Native Windows Build
+  - Installing GNUWin32
+* Cygwin Build Problems
+  - Strange Path Problems
+  - Window Native Toolchain Issues
+* Documentation
+
+# INTRODUCTION
+
+Apache NuttX (Incubating) is a real-time operating system (RTOS) with an
+emphasis on standards compliance and small footprint.  Scalable from 8-bit
+to 32-bit microcontroller environments, the primary governing standards in
+NuttX are POSIX and ANSI standards. Additional standard APIs from Unix and
+other common RTOSs (such as VxWorks) are adopted for functionality not
+available under these standards, or for functionality that is not
+appropriate for deeply-embedded environments (such as fork()).
+
+Extensive documentation can be found on the project wiki:
+  <https://cwiki.apache.org/NUTTX/Nuttx>
+
+## Incubation Status
+
+Apache NuttX (Incubating) is an effort undergoing Incubation at The Apache
+Software Foundation (ASF), sponsored by the Incubator.  For more on our
+incubation effort, please see the file DISCLAIMER-WIP, in the same
+directory as this README.
+
+For brevity, the rest of this file will refer to it as Apache NuttX or
+simply NuttX.
+
+# COMMUNITY
+
+Every volunteer project obtains its strength from the people involved in
+it.  We invite you to participate as much or as little as you choose.
+
+We encourage you to:
+
+  - Use our project and provide feedback.
+  - Provide us with use-cases.
+  - Report bugs and submit patches.
+  - Contribute code or documentation.
+
+## Getting Help
+
+The best place to get help is the developer's mailing list.  Please see
+the following section:
+
+## Mailing Lists
+
+Get help using NuttX or contribute to the project on our mailing lists:
+
+  * <de...@nuttx.apache.org> is for people who want to contribute code to NuttX.
+    * To subscribe, send an email to <de...@nuttx.apache.org>.
+    * To unsubscribe, send an email to <de...@nuttx.apache.org>.
+    * View the archives at:
+      <https://www.mail-archive.com/dev@nuttx.apache.org/>
+
+  * <co...@nuttx.apache.org> is a read-only list that notifies subscribers
+  about commit messages and patches to NuttX.
+    * To subscribe, send an email to <co...@nuttx.apache.org>.
+    * To unsubscribe, send an email to <co...@nuttx.apache.org>.
+    * View the archives at:
+      <https://www.mail-archive.com/commits@nuttx.apache.org/>
+
+## Issue Tracker
+
+### Bug Reports:
+
+Found bug? Send an email to the dev list: <de...@nuttx.apache.org>
+
+Before submitting an issue, please:
+
+  - Verify that the bug does in fact exist. 
+  
+  - Search the mailing list archives to verify there is no existing issue
+    reporting the bug you've found.
+ 
+  - Consider tracking down the bug yourself in the NuttX source code and
+    submitting a patch along with your bug report.  This is a great time
+    saver for the NuttX developers and helps ensure the bug will be fixed
+    quickly.
+  
+### Feature Requests:
+  
+Enhancement requests for new features are also welcome. The more concrete
+and rational the request is, the greater the chance it will incorporated
+into future releases.
+
+## Source Code
+
+The project sources are in two Git repositories.  The core OS is in
+incubator-nuttx and the apps repository is in incubator-nuttx-apps.  These
+are housed in GitBox on ASF servers and also mirrored at GitHub.  These
+are kept in sync, so you can use whichever option you prefer.
+
+  - NuttX core OS repository:
+    
+    - Primary:
+      <https://gitbox.apache.org/repos/asf?p=incubator-nuttx.git>
+    
+    - GitHub Mirror:
+      <https://github.com/apache/incubator-nuttx>
+  
+  - Apps repository:
+    
+    - Primary:
+      <https://gitbox.apache.org/repos/asf?p=incubator-nuttx-apps.git>
+    
+    - GitHub Mirror:
+      <https://github.com/apache/incubator-nuttx-apps>
+
+## Website Source Code
+
+The project website sources are accessible via the website source code
+  repository which is also mirrored in GitHub:
+
+- Primary:
+  <https://gitbox.apache.org/repos/asf?p=incubator-nuttx-website.git>
+
+- GitHub Mirror:
+  <https://github.com/apache/incubator-nuttx-website>
+
+# ENVIRONMENTS
+
+  NuttX requires a POSIX development environment such as you would find under
+  Linux or macOS.  NuttX may also be installed and built on Windows system
+  if you also provide such a POSIX development environment.  Options for a
+  POSIX development environment under Windows include:
+
+  - An installation of Linux on a virtual machine (VM) in Windows.  I have
+    not been happy using a VM myself.  I have had stability problems with
+    open source VMs and commercial VMs cost more than I want to spend.
+    Sharing files with Linux running in a VM is awkward;  sharing devices
+    connected to the Windows box with Linux in a VM is, at the very least,
+    confusing;  Using Windows tools (such as Segger J-Link) with files
+    built under the Linux VM is not a possibility.
+
+  - The Cygwin environment.  Instructions for installation of Cygwin on a
+    Windows system are provided in the following paragraph, "Installing
+    Cygwin".  Cygwin is a mature, well-tested, and very convenient
+    environment.  It is especially convenient if you  need to
+    integrate with Windows tools and files.  Downsides are that the
+    installation time is very long and the compile times are slow.
+
+  - Ubuntu/Bash shell under Windows 10.  This is a new option under
+    Windows 10.  See the section "Ubuntu Bash under Windows 10" below.
+    This is an improvement over Cygwin if your concern is compile time;
+    its build performance is comparable to native Linux, certainly better
+    than the Cygwin build time.  It also installs in a tiny fraction of
+    the time as Cygwin, perhaps 20 minutes for the basic Ubuntu install
+    (vs. more than a day for the complete Cygwin install).
+  
+    There have been even more recent ports of Linux environment to
+    Windows.  I need to update this section to include some mention of
+    these alternatives.
+
+  - The MSYS environment.  MSYS derives from an older version of Cygwin
+    simplified and adapted to work more naturally in the Windows
+    environment.  See <http://www.mingw.org/wiki/MSYS> if you are
+    interested in using MSYS.  The advantages of the MSYS environment is
+    that it is better integrted with the native Windows environment and
+    lighter weight; it uses only a  minimal number of add-on POSIX-land
+    tools.
+  
+    The download link in that Wiki takes you to the SourceForge download
+    site.  The SourceForge MSYS project has been stagnant for some time.
+    The MSYS project has more recently moved to
+    <http://odsn.net/projects/sfnet_mingwbundle>.  Downloads of current .zip
+    files are available there but no instructions for the installation.
+
+  - MSYS2 appears to be a re-write of MSYS based on a newer version of
+    Cygwin.  Is it available at <https://www.msys2.org>.  A windows
+    installer is available at that site along with very good installation
+    instructions.  The download is relatively quick (at least compared to
+    Cygwin) and the 'pacman' package management tool supports supports
+    simple system updates.  For example, 'pacman -S git' will install the
+    GIT command line utilities.
+
+  - Other POSIX environments.  Check out:
+    
+    - UnxUtils: <https://sourceforge.net/projects/unxutils/>,
+      <https://en.wikipedia.org/wiki/UnxUtils>
+    - MobaXterm: <https://mobaxterm.mobatek.net/>
+    - Gow: <https://github.com/bmatzelle/gow/wiki>
+  
+    **Disclaimer**:  In principle, these should work.  However, I have never
+    used any of these environments and cannot guarantee that there is
+    not some less-than-obvious issues.
+  
+NuttX can also be installed and built on a native Windows system, but with
+some potential tool-related issues (see the discussion "Native Windows
+Build" under "Building NuttX" below).  GNUWin32 is used to provide
+compatible native windows tools.
+
+## Installing Cygwin
+
+Installing Cygwin on your Windows PC is simple, but time consuming.  See
+<http://www.cygwin.com/> for installation instructions. Basically you just
+need to download a tiny setup.exe program and it does the real, network
+installation for you.
+
+Some Cygwin installation tips:
+
+  1. Install at `C:\cygwin`
+  
+  2. Install **everything**:  "Only the minimal base packages from the
+     Cygwin distribution are installed by default. Clicking on categories
+     and packages in the setup.exe package installation screen will
+     provide you with the ability to control what is installed or updated.
+     Clicking on the "Default" field next to the "All" category will
+     provide you with the opportunity to install every Cygwin package.
+     Be advised that this will download and install hundreds of megabytes
+     to your computer."
+   
+If you use the "default" installation, you will be missing many
+of the Cygwin utilities that you will need to build NuttX.  The
+build will fail in numerous places because of missing packages.
+
+NOTE: The last time I installed **everything**, the download was
+about 5GiB.  The server I selected was also very slow so it took
+over a day to do the whole install!
+
+NOTE: You don't really have to install **everything** but I cannot
+answer the question "Then what should I install?"  I don't know
+the answer to that and so will continue to recommend installing
+**everything**.
+
+You should certainly be able to omit "Science", "Math", and
+"Publishing".  You can try omitting KDE, Gnome, GTK, and other
+graphics packages if you don't plan to use them.
+
+Perhaps a minimum set would be those packages listed below for the
+"Ubuntu Bash under Windows 10" installation?
+
+**UPDATE**:  Sergey Frolov had success with the following minimal
+Cygwin configuration:
+   
+   1. After starting the Cygwin installer, keep the recommended
+      packages that are pre-selected in the default configuration.
+   
+   2. Using the installation tools, add the following packages:
+      
+        make (GNU make)  bison        libgmp3-dev
+        gcc-core         byacc        libmpfr-dev
+        gcc-g++          gperf        libmpc-dev
+        flex             gdb          automake-1.15
+        libncurses-dev   libgmp-dev
+   
+After installing Cygwin, you will get lots of links for installed
+tools and shells.  I use the RXVT native shell.  It is fast and reliable
+and does not require you to run the Cygwin X server (which is neither
+fast nor reliable).  Unless otherwise noted, the rest of these
+instructions assume that you are at a bash command line prompt in
+either Linux or in Cygwin shell.
+
+## Using MSYS
+
+MSYS is an environment the derives from Cygwin.  Thus, most things said
+about Cygwin apply equally to MSYS.  This section will, then, focus on
+the differences when using MSYS, specifically MSYS2.
+
+Here is it assumed that you have already downloaded and installed MSYS2
+from https://www.msys2.org using the windows installer available at that
+location.  It is also assumed that you have brought in the necessary
+tools using the 'pacman' package management tool Tools needed including:
+
+  pacman -S git
+  pacman -S make
+  pacman -S gcc
+  pacman -S gdb
+
+And possibly others depending upon your usage.  Then you will need to
+build and install kconfig-frontends per the instructions of the top-level
+README.txt file in the tools repository.  This requires the following
+additional tools:
+
+    pacman -S bison
+    pacman -S gperf
+    pacman -S ncurses-devel
+    pacman -S automake-wrapper
+    pacman -S autoconf
+    pacman -S pkg-config
+
+Because of some versioning issues, I had to run 'aclocal' prior to
+running the kconfig-frontends configure script.  See "Configuring NuttX"
+below for further information.
+
+Unlike Cygwin, MSYS does not support symbolic links.  The 'ln -s' command
+will, in fact, copy a directory!  This means that you Make.defs file will
+have to include definitions like:
+
+    ifeq ($(CONFIG_WINDOWS_MSYS),y)
+      DIRLINK = $(TOPDIR)/tools/copydir.sh
+      DIRUNLINK = $(TOPDIR)/tools/unlink.sh
+    endif
+
+This will force the directory copies to work in a way that can be handled
+by the NuttX build system.  NOTE:  The default link.sh script has been
+updated so that is should now be MSYS2 compatible.  The above is preferred
+but no longer necessary in the Make.defs file.
+
+To build the simulator under MSYS, you also need:
+
+    pacman -S zlib-devel
+
+It appears that you cannot use directory names with spaces in them like
+"/c/Program\ Files \(86\)" in the MSYS path variable.  I worked around this
+by create Windows junctions like this:
+
+  1. Open the a windows command terminal,
+  
+  2. CD to `c:\msys64`, then
+  
+  3. `mklink /j programfiles "C:/Program\ Files"` and
+  
+  4. `mklink /j programfiles86 "C:/Program\ Files\ \(x86\)"`
+     
+     They then show up as `/programfiles` and `/programfiles86` with the MSYS2
+     sandbox.  Those paths can then be used with the PATH variable.  I had
+     to do something similar for the path to the GNU Tools "ARM Embedded
+     Toolchain" which also has spaces in the path name.
+
+## Ubuntu Bash under Windows 10
+
+A better version of a command-line only Ubuntu under Windows 10 (beta)
+has recently been made available from Microsoft.
+
+### Installation
+
+Installation instructions abound on the Internet complete with screen
+shots.  I will attempt to duplicate those instructions in full here.
+Here are the simplified installation steps:
+
+  - Open *Settings*.
+  
+  - Click on *Update & security*.
+  
+  - Click on *For Developers*.
+  
+  - Under *Use developer features*, select the *Developer mode* option to
+    setup the environment to install Bash.
+  
+  - A message box should pop up.  Click *Yes* to turn on developer mode.
+  
+  - After the necessary components install, you'll need to restart your
+    computer.
+    
+    Once your computer reboots:
+  
+  - Open *Control Panel*.
+  
+  - Click on *Programs*.
+  
+  - Click on *Turn Windows features on or off*.
+  
+  - A list of features will pop up, check the *Windows Subsystem for Linux
+    (beta)* option.
+  
+  - Click *OK*.
+  
+  - Once the components installed on your computer, click the *Restart
+    now* button to complete the task.
+    
+    After your computer restarts, you will notice that Bash will not appear in
+    the *Recently added* list of apps, this is because Bash isn't actually
+    installed yet. Now that you have setup the necessary components, use the
+    following steps to complete the installation of Bash:
+  
+  - Open *Start*, do a search for `bash.exe`, and press *Enter*.
+  
+  - On the command prompt, type `y` and press Enter to download and install
+    Bash from the Windows Store.  This will take awhile.
+  
+  - Then you'll need to create a default UNIX user account. This account
+    doesn't have to be the same as your Windows account. Enter the
+    username in the required field and press Enter (you can't use the
+    username `admin`).
+  
+  - Close the `bash.exe` command prompt.
+  
+  Now that you completed the installation and setup, you can open the Bash
+  tool from the Start menu like you would with any other app.
+
+### Accessing Windows Files from Ubuntu
+
+File systems will be mounted under `/mnt` so for example `C:\Program Files`
+appears at `/mnt/c/Program Files`.  This is as opposed to Cygwin where
+the same directory would appear at `/cygdrive/c/Program Files`.
+
+With these differences (perhaps a few other Windows quirks) the Ubuntu
+install works just like Ubuntu running natively on your PC.
+
+A good tip for file sharing is to use symbolic links within your Ubuntu
+home directory.  For example, suppose you have your `projects` directory
+at `C:\Documents\projects`.  Then you can set up a link to the `projects/`
+directory in your Ubuntu directory like:
+
+    ln -s /mnt/c/Documents/projects projects
+
+### Accessing Ubuntu Files From Windows
+
+In Ubuntu Userspace for Windows, the Ubuntu file system root directory is
+at:
+
+    %localappdata%\lxss\rootfs
+
+Or
+
+    C:\Users\Username\AppData\Local\lxss\rootfs
+
+However, I am unable to see my files under the rootfs\home directory.
+After some looking around, I find the home directory
+`%localappdata%\lxss\home`.
+
+With that trick access to the `/home` directory, you should actually be
+able to use Windows tools outside of the Ubuntu sandbox with versions of
+NuttX built within the sandbox using that path.
+
+### Executing Windows Tools from Ubuntu
+
+You can also execute Windows tools from within the Ubuntu sandbox:
+
+    /mnt/c/Program\ Files\ \(x86\)/Microchip/xc32/v1.43/bin/xc32-gcc.exe --version
+    Unable to translate current working directory. Using C:\WINDOWS\System32
+    xc32-gcc.exe (Microchip Technology) 4.8.3 MPLAB XC32 Compiler v1.43 Build date: Mar  1 2017
+    ...
+
+The error message indicates that there are more issues:  You cannot mix
+Windows tools that use Windows style paths in an environment that uses
+POSIX paths.  I think you would have to use Linux tools only from within
+the Ubuntu sandbox.
+
+### Install Ubuntu Software
+
+Use `sudo apt-get install <package name>`.  As examples, this is how
+you would get GIT:
+
+    sudo apt-get install git
+
+This will get you a compiler for your host PC:
+
+    sudo apt-get install gcc
+
+This will get you an ARM compiler for your target:
+
+    sudo apt-get install gcc-arm-none-eabi
+
+**NOTE**: That is just an example.  I am not sure if apt-get will give you a
+current or usable compiler.  You should carefully select your toolchain
+for the needs of your project.
+
+You will also need to get the kconfig-frontends configuration as
+described below under *NuttX Configuration Tool*.  In order to build the
+kconfig-frontends configuration tool you will also need: `make`, `gperf`,
+`flex`, `bison`, and `libncurses-dev`.
+
+That is enough to do a basic NuttX build.
+
+### Integrating with Windows Tools
+
+If you want to integrate with Windows native tools, then you would need
+deal with the same kind of craziness as with integrating Cygwin with
+native toolchains, see the section *Cygwin Build Problems* below.
+
+However, there is currently no build support for using Windows native
+tools with Ubuntu under Windows.  This tool combination is made to work
+with Cygwin through the use of the `cygpath -w` tool that converts paths
+from say `/cydrive/c/Program Files` to `C:\Program Files`.  There is,
+however, no corresponding tool to convert `/mnt/c/Program Files` in the
+Ubuntu environment.
+
+### Graphics Support
+
+The Ubuntu version support by Microsoft is a command-line only version.
+There is no support for Linux graphics utilities.
+
+This limitation is not a limitation of Ubuntu, however, only in what
+Microsoft is willing to support.  If you install a X-Server, then you
+can also use basic graphics utilities.  See for example:
+
+  <http://www.howtogeek.com/261575/how-to-run-graphical-linux-desktop-applications-from-windows-10s-bash-shell/>
+
+Many Linux graphics programs would, however, also require a graphics
+framework like GTK or Qt.  So this might be a trip down the rabbit hole.
+
+### Using macOS
+
+You need to install at least the following tools specific to macOS.
+
+  * flock (used by APPDIR build logic)
+    
+A macOS port is available at: <https://github.com/discoteq/flock>
+  
+    brew tap discoteq/discoteq
+    brew install flock
+  
+  If you want to build the sim:
+
+  * Xcode (the native compiler and the rest of the toolchain)
+
+  * ELF toolchain (if you want to build modules for CONFIG_LIBC_MODLIB)
+
+    brew install x86_64-elf-gc
+
+# INSTALLATION
+
+There are two ways to get NuttX:  You may download released, stable
+tarballs from either the project website.  Or you may get NuttX by
+cloning the GIT repositories.  Let's consider the released tarballs
+first:
+
+## Download and Unpack
+
+Download and unpack the NuttX tarball.  If you are reading this, then
+you have probably already done that.  After unpacking, you will end
+up with a directory called nuttx-version (where version is the NuttX
+version number). You might want to rename that directory nuttx to
+match the various instructions in the documentation and some scripts
+in the source tree.
+
+  * Download location:
+  
+    <https://nuttx.apache.org/download/>
+  
+  * Legacy download locations:
+
+    <https://bitbucket.org/nuttx/nuttx/downloads>  
+    <https://sourceforge.net/projects/nuttx/files/nuttx/>
+
+## Semi-Optional apps/ Package
+
+All NuttX libraries and example code used to be in included within
+the NuttX source tree.  As of NuttX-6.0, this application code was
+moved into a separate tarball, the apps tarball.  If you are just
+beginning with NuttX, then you will want to download the versioned
+apps tarball along with the NuttX tarball.  If you already have your
+own product application directory, then you may not need the apps
+tarball.
+
+It is called "Semi-optional" because if you don't have some `apps/`
+directory, NuttX will *fail* to build! You do not necessarily need
+to use the NuttX apps tarball but may, instead, provide your own
+custom application directory.  Such a custom directory would need
+to include a valid Makefile to support the build and a valid Kconfig
+file to support the configuration.  More about these files later.
+
+Download then unpack the apps tarball in the same directory where you
+unpacked the NuttX tarball.  After you unpack the apps tarball, you
+will have a new directory called apps-version (where the version
+should exactly match the version of the NuttX tarball).  Again, you
+might want to rename the directory to simply apps/ to match what
+you read in the documentation
+
+After unpacking (and renaming) the apps tarball, you will have two
+directories side by side like this:
+
+             |
+        +----+----+
+        |         |
+      nuttx/     apps/
+
+This is important because the NuttX build will expect to find the
+apps directory in that (default) location.  That default location
+can be changed by modifying your NuttX configuration file, but that
+is another story.
+
+## Installation Directories with Spaces in the Path
+
+The nuttx build directory should reside in a path that contains no
+spaces in any higher level directory name.  For example, under
+Cygwin, your home directory might be formed from your first and last
+names like: `/home/First Last`. That will cause strange errors when
+the make system tries to build.
+
+[Actually, that problem is probably not too difficult to fix.  Some
+ Makefiles probably just need some paths within double quotes]
+
+I work around spaces in the home directory name, by creating a
+new directory that does not contain any spaces, such as `/home/nuttx`.
+Then I install NuttX in `/home/nuttx` and always build from
+`/home/nuttx/nuttx-code`.
+
+## Downloading from Repositories
+
+### Cloning the Repository
+
+**BEFORE** cloning repositories on any Windows platform do the following GIT
+command:
+
+    git config --global core.autocrlf false
+
+That will avoid conversions of linefeeds (newlines, \n) to carriage
+return plus linefeed sequences (\r\n)
+
+The current NuttX du jour is available in from a GIT repository.  Here are
+instructions for cloning the core NuttX RTOS (corresponding to the nuttx
+tarball discussed above):
+
+    git clone https://gitbox.apache.org/repos/asf/incubator-nuttx.git nuttx
+
+-or-
+
+    git clone https://github.com/apache/incubator-nuttx.git nuttx
+
+And the semi-optional apps/ application directory and be cloned like:
+
+    git clone https://gitbox.apache.org/repos/asf/incubator-nuttx-apps.git apps
+  
+-or-
+  
+    git clone https://github.com/apache/incubator-nuttx-apps.git apps
+
+That will give you the same directory structure like this:
+    
+             |
+        +----+----+
+        |         |
+      nuttx/     apps/
+
+### Configuring the Clones
+
+The following steps need to be performed for each of the repositories.
+After changing to the clone directory:
+
+Set your identity:
+
+    git config --global user.name "My Name"
+    git config --global user.email my.name@example.com
+  
+Colorized diffs are much easier to read:
+
+    git config --global color.branch auto
+    git config --global color.diff auto
+    git config --global color.interactive auto
+    git config --global color.status auto
+
+Checkout other settings
+
+    git config --list
+
+### Cloning NuttX Inside Cygwin
+
+If you are cloning the NuttX repository, it is recommended to avoid
+automatic end of lines conversions by git. These conversions may break
+some scripts like configure.sh. Before cloning, do the following:
+
+    git config --global core.autocrlf false
+
+## Related Repositories
+
+These are standalone repositories:
+
+  * <https://gitbox.apache.org/repos/asf/incubator-nuttx-apps>  
+    or  
+    <https://github.com/apache/incubator-nuttx-apps.git>
+    
+    This directory holds an optional package of applications and libraries
+    can be used with the NuttX RTOS.  There is a README.txt file there that
+    will provide more information about that package.
+
+  * <https://bitbucket.org/nuttx/nxwidgets>
+  
+    This is the NuttX C++ graphics support.  This includes NxWM, the tiny
+    NuttX Window Manager.
+
+  * <https://bitbucket.org/nuttx/uclibc>
+  
+    This repository contains a version of the uClibc++ C++ library.  This code
+    originates from <http://cxx.uclibc.org/> and has been adapted for NuttX by the
+    RGMP team (<http://rgmp.sourceforge.net/wiki/index.php/Main_Page>).
+
+  * <https://bitbucket.org/nuttx/buildroot>
+  
+    A environment that you can to use to build a custom, NuttX GNU toolchain.
+
+  * <https://bitbucket.org/nuttx/tools>
+  
+    There are snapshots of some tools here that you will need to work with
+    NuttX:  kconfig-frontends, genromfs, and others.
+
+## Notes about Header Files
+
+### Other C-Library Header Files
+
+When a GCC toolchain is built, it must be built against a C library.
+The compiler together with the contents of the C library completes the
+C language definition and provides the complete C development
+environment.  NuttX provides its own, built-in C library.  So the
+complete, consistent C language definition for use with NuttX comes from
+the combination of the compiler and the header files provided by the
+NuttX C library.
+
+When a GCC toolchain is built, it incorporates the C library header
+files into the compiler internal directories and, in this way, the C
+library really becomes a part of the toolchain.  If you use the NuttX
+buildroot toolchain as described below under "NuttX Buildroot
+Toolchain", your GCC toolchain will build against the NuttX C library
+and will incorporate the NuttX C library header files as part of the
+toolchain.
+
+If you use some other, third-party tool chain, this will not be the
+case, however.  Those toolchains were probably built against some
+other, incompatible C library distribution (such as newlib).  Those
+tools will have incorporated the incompatible C library header files
+as part of the toolchain.  These incompatible header files must *not*
+be used with NuttX because they will conflict with definitions in the
+NuttX built-in C-Library.  For such toolchains that include header
+files from a foreign C-Library, NuttX must be compiled without using
+the standard header files that are distributed with your toolchain.
+This prevents including conflicting, incompatible header files such
+as stdio.h.
+
+The math.h and stdarg.h are probably the two most trouble some header
+files to deal with.  These troublesome header files are discussed in
+more detail below.
+
+### Header Files Provided by Your Toolchain
+
+Certain header files, such as `setjmp.h`, `stdarg.h`, and `math.h`, may still
+be needed from your toolchain and your compiler may not, however, be able
+to find these if you compile NuttX without using standard header files
+(i.e., with `-nostdinc`).  If that is the case, one solution is to copy
+those header file from your toolchain into the NuttX include directory.
+
+### Duplicated Header Files
+
+There are also a few header files that can be found in the `nuttx/include`
+directory which are duplicated by the header files from your toolchain.
+stdint.h and stdbool.h are examples.  If you prefer to use the `stdint.h`
+and `stdbool.h` header files from your toolchain, those could be copied
+into the `nuttx/include/` directory. Using most other header files from
+your toolchain would probably cause errors.
+
+### math.h
+
+Even though you should not use a foreign C-Library, you may still need
+to use other, external libraries with NuttX.  In particular, you may
+need to use the math library, libm.a.  NuttX supports a generic, built-in
+math library that can be enabled using `CONFIG_LIBM=y`.  However, you may
+still want to use a higher performance external math library that has
+been tuned for your CPU.  Sometimes such tuned math libraries are
+bundled with your toolchain.
+
+The math library header file, `math.h`, is a then special case.  If you do
+nothing, the standard math.h header file that is provided with your
+toolchain will be used.
+
+If you have a custom, architecture specific math.h header file, then
+that header file should be placed at `arch/<cpu>/include/math.h`.  There
+is a stub `math.h` header file located at `include/nuttx/lib/math.h`.  This stub
+header file can be used to "redirect" the inclusion to an architecture-
+specific math.h header file.  If you add an architecture specific math.h
+header file then you should also define `CONFIG_ARCH_MATH_H=y` in your
+NuttX Configuration file.  If `CONFIG_ARCH_MATH_H` is selected, then the
+top-level Makefile will copy the stub math.h header file from
+`include/nuttx/lib/math.h` to `include/math.h` where it will become the system
+`math.h` header file.  The stub `math.h` header file does nothing other
+than to include that architecture-specific `math.h` header file as the
+system `math.h` header file.
+
+### float.h
+
+If you enable the generic, built-in math library, then that math library
+will expect your toolchain to provide the standard `float.h` header file.
+The float.h header file defines the properties of your floating point
+implementation.  It would always be best to use your toolchain's `float.h`
+header file but if none is available, a default `float.h` header file will
+be provided if this option is selected.  However, there is no assurance
+that the settings in this `float.h` are actually correct for your platform!
+
+### stdarg.h
+
+In most cases, the correct version of stdarg.h is the version provided
+with your toolchain.  However, sometimes there are issues with
+using your toolchains `stdarg.h`.  For example, it may attempt to draw in
+header files that do not exist in NuttX or perhaps the header files that
+it uses are not compatible with the NuttX header files.  In those cases,
+you can use an architecture-specific `stdarg.h` header file by defining
+`CONFIG_ARCH_STDARG_H=y`.
+
+See the discussion above for the `math.h` header.  This setting works
+exactly the same for the `stdarg.h` header file.
+
+# CONFIGURING NUTTX
+
+## Instantiating "Canned" Configurations
+
+### `configure.sh` and `configure.bat`
+
+"Canned" NuttX configuration files are retained in:
+
+    boards/<arch-name>/<chip-name>/<board-name>/configs/<config-dir>
+
+Where `<board-name>` is the name of your development board and `<config-dir>`
+is the name of the sub-directory containing a specific configuration for
+that board. `<arch-name>` and `<chip-name>` refer to characteristics of the
+MCU used on the board: `<arch-name>` is the CPU architecture implemented
+by the MCU; `<chip-name>` identifies the MCU chip family.  Only a few
+steps are required to instantiate a NuttX configuration, but to make the
+configuration even easier there are scripts available in the tools/
+sub-directory combines those simple steps into one command.
+
+There is one tool for use with any Bash-like shell that does configuration
+steps.  It is used as follows:
+
+    tools/configure.sh <board-name>:<config-dir>
+
+There is an alternative Windows batch file that can be used in the windows
+native environment like:
+
+    tools\configure.bat <board-name>:<config-dir>
+
+And, to make sure that other platforms are supported, there is also a
+C program at tools/configure.c that can be compiled to establish the
+board configuration.
+
+See `tools/README.txt` for more information about these scripts.
+
+General information about configuring NuttX can be found in:
+
+    {TOPDIR}/boards/README.txt
+    {TOPDIR}/boards/<arch-name>/<chip-name>/<board-name>/README.txt
+
+### The Hidden Configuration Scripts:
+
+As mentioned above, there are only a few simple steps to instantiating a
+NuttX configuration.  Those steps are hidden by the configuration scripts
+but are summarized below:
+  
+  1. Copy Files
+  
+     Configuring NuttX requires only copying two files from the
+     `<config-dir>` to the directory where you installed NuttX (TOPDIR):
+  
+       * Copy `boards/<arch-name>/<chip-name>/<board-name>/configs/<config-dir>/Make.def` to `{TOPDIR}/Make.defs`
+    
+         OR
+    
+       * Copy `boards/<arch-name>/<chip-name>/<board-name>/scripts/Make.def`
+         to `{TOPDIR}/Make.defs`
+    
+         Make.defs describes the rules needed by your tool chain to compile
+         and link code.  You may need to modify this file to match the
+         specific needs of your toolchain.  NOTE that a configuration may
+         have its own unique Make.defs file in its configuration directory or
+         it may use a common Make.defs file for the board in the scripts/
+         directory.  The first takes precedence.
+    
+       * Copy `boards/<arch-name>/<chip-name>/<board-name>/configs/<config-dir>/defconfig` to `{TOPDIR}/.config`
+    
+         The defconfig file holds the actual build configuration.  This
+         file is included by all other make files to determine what is
+         included in the build and what is not.  This file is also used
+         to generate a C configuration header at `include/nuttx/config.h`.
+    
+       * Copy other, environment-specific files to `{TOPDIR}`
+    
+         This might include files like .gdbinit or IDE configuration files
+         like .project or .cproject.
+  
+  2. Refresh the Configuration
+  
+     New configuration setting may be added or removed.  Existing settings
+     may also change there values or options.  This must be handled by
+     refreshing the configuration as described below.
+    
+     NOTE:  NuttX uses only compressed defconfig files.  For the NuttX
+     defconfig files, this refreshing step is *NOT* optional; it is also
+     necessary to uncompress and regenerate the full making file.  This is
+     discussed further below.
+
+## Refreshing Configurations
+
+Configurations can get out of date.  As new configuration settings are
+added or removed or as dependencies between configuration settings
+change, the contents of a default configuration can become out of synch
+with the build systems.  Hence, it is a good practice to "refresh" each
+configuration after configuring and before making.  To refresh the
+configuration, use the NuttX Configuration Tool like this:
+
+    make oldconfig
+
+AFTER you have instantiated the NuttX configuration as described above.
+The configuration step copied the .config file into place in the top-level
+NuttX directory; 'make oldconfig' step will then operate on that .config
+file to bring it up-to-date.
+
+If your configuration is out of date, you will be prompted by 'make oldconfig'
+to resolve the issues detected by the configuration tool, that is, to
+provide values for the new configuration options in the build system.  Doing
+this can save you a lot of problems down the road due to obsolete settings in
+the default board configuration file.  The NuttX configuration tool is
+discussed in more detail in the following paragraph.
+
+Confused about what the correct value for a new configuration item should
+be?  Enter ? in response to the 'make oldconfig' prompt and it will show
+you the help text that goes with the option.
+
+If you don't want to make any decisions are willing to just accept the
+recommended default value for each new configuration item, an even easier
+way is:
+
+    make olddefconfig
+
+The olddefconfig target will simply bring your configuration up to date with
+the current Kconfig files, setting any new options to the default value.
+No questions asked.
+
+## NuttX Configuration Tool
+
+An automated tool has been incorporated to support re-configuration
+of NuttX.  This tool is based on the kconfig-frontends application available
+at <https://bitbucket.org/nuttx/tools/src/master/kconfig-frontends/>.  (This
+is a snapshot of the old <http://ymorin.is-a-geek.org/projects/kconfig-frontends>
+which is no longer available.)  This application provides a tool called
+`kconfig-mconf` that is used by the NuttX top-level Makefile. The following
+make target is provided:
+
+    make menuconfig
+
+This make target will bring up NuttX configuration menus.
+
+**WARNING**:  Never do `make menuconfig` on a configuration that has
+not been converted to use the kconfig-frontends tools!  This will
+damage your configuration (see
+<http://www.nuttx.org/doku.php?id=wiki:howtos:convertconfig>).
+
+How do we tell a new configuration from an old one? See "Incompatibilities
+with Older Configurations" below.
+
+The `menuconfig` make target depends on two things:
+
+  1. The Kconfig configuration data files that appear in almost all
+     NuttX directories.  These data files are the part that is still
+     under development (patches are welcome!).  The Kconfig files
+     contain configuration information for the configuration settings
+     relevant to the directory in which the Kconfig file resides.
+     
+     NOTE: For a description of the syntax of this configuration file,
+     see kconfig-language.txt in the tools repository at
+     <https://bitbucket.org/nuttx/tools>
+  
+  2. The `kconfig-mconf` tool. `kconfig-mconf` is part of the
+     kconfig-frontends package.  You can download that package from the
+     snapshot in the tools repository at <https://bitbucket.org/nuttx/tools>.
+  
+     Building kconfig-frontends under Linux may be as simple as
+     `configure; make; make install` but there may be some build
+     complexities, especially if you are building under Cygwin.  See
+     the more detailed build instructions in the top-level README.txt
+     file of the tools repository at <https://bitbucket.org/nuttx/tools>.
+  
+  
+     The `make install` step will, by default, install the `kconfig-mconf`
+     tool at `/usr/local/bin/mconf`.  Where ever you choose to
+     install `kconfig-mconf`, make certain that your PATH variable includes
+     a path to that installation directory.
+  
+     The kconfig-frontends tools will not build in a native Windows
+     environment directly "out-of-the-box".  For the Windows native
+     case, you can use the modified version of kconfig-frontends
+     that can be found at
+
+     <http://uvc.de/posts/linux-kernel-configuration-tool-kconfig-under-windows.html>  
+
+     or a more recent port that can be found at  
+
+     <http://reclonelabs.com/more-kconfig-awesomeness-for-windows/>.
+   
+The basic configuration order is "bottom-up":
+   
+   - Select the build environment,
+   - Select the processor,
+   - Select the board,
+   - Select the supported peripherals
+   - Configure the device drivers,
+   - Configure the application options on top of this.
+   
+This is pretty straight forward for creating new configurations
+but may be less intuitive for modifying existing configurations.
+
+Another ncurses-based tool that is an option to kconfig-mconf is
+kconfig-nconf.  The differences are primary in in the aesthetics of the
+UI.  If you have kconfig-nconf built, then you can invoke that front end
+with:
+   
+     make nconfig
+   
+If you have an environment that supports the Qt or GTK graphical systems
+(probably KDE or gnome, respectively, or Cygwin under Windows with Qt or
+GTK installed), then you can also build the graphical kconfig-frontends,
+kconfig-qconf and kconfig-gconf.  In these case, you can start the
+graphical configurator with either:
+   
+     make qconfig
+   
+ or
+   
+     make gconfig
+   
+Some keyboard shortcuts supported by kconfig-mconf, the tool that runs
+when you do 'make menuconfig':
+
+   - `?` will bring up the mconfig help display.
+   
+   - `/` can be used find configuration selections.
+   
+   - `Z` can be used to reveal hidden configuration options
+   
+These last two shortcuts are described further in the following
+paragraphs.
+
+## Finding Selections in the Configuration Menus
+
+The NuttX configuration options have gotten complex and it can be very
+difficult to find options in the menu trees if you are not sure where
+to look.  The "basic configuration order" describe above can help to
+narrow things down.
+
+But if you know exactly what configuration setting you want to select,
+say CONFIG_XYZ, but not where to find it, then the 'make menuconfig'
+version of the tool offers some help:  By pressing the '/' key, the
+tool will bring up a menu that will allow you to search for a
+configuration item.  Just enter the string CONFIG_XYZ and press 'ENTER'.
+It will show you not only where to find the configuration item, but
+also all of the dependencies related to the configuration item.
+
+## Reveal Hidden Configuration Options
+
+If you type `Z`, then kconfig-mconf will change what is displayed.
+Normally, only enabled features that have all of their dependencies met
+are displayed.  That is, of course, not very useful if you would like to
+discover new options or if you are looking for an option and do not
+realize that the dependencies have not yet been selected and, hence, it
+is not displayed.
+
+But if you enter `Z`, then every option will be shown, whether or not its
+dependencies have been met.  You can then see everything that could be
+selected with the right dependency selections.  These additional options
+will be shown the `-` for the selection and for the value (since it
+cannot be selected and has no value).  About all you do is to select
+the `<Help>` option to see what the dependencies are.
+
+## Make Sure that You are on the Right Platform
+
+Saved configurations may run on Linux, Cygwin (32- or 64-bit), or other
+platforms.  The platform characteristics can be changed use `make
+menuconfig`.  Sometimes this can be confusing due to the differences
+between the platforms.  Enter sethost.sh
+
+sethost.sh is a simple script that changes a configuration to your
+host platform.  This can greatly simplify life if you use many different
+configurations.  For example, if you are running on Linux and you
+configure like this:
+
+    tools/configure.sh board:configuration
+
+The you can use the following command to both (1) make sure that the
+configuration is up to date, AND (2) the configuration is set up
+correctly for Linux:
+
+    tools/sethost.sh -l
+
+Or, if you are on a Windows/Cygwin 64-bit platform:
+
+    tools/sethost.sh -c
+
+Or, for MSYS/MSYS2:
+
+    tools/sethost.sh -g
+
+Other options are available from the help option built into the
+script.  You can see all options with:
+
+    tools/sethost.sh -h
+
+Recently, the options to the configure.sh (and configure.bat) scripts have
+been extended so that you both setup the configuration, select for the host
+platform that you use, and uncompress and refresh the defconfig file all in
+one command like:
+
+    tools/configure.sh -l board:configuration
+
+For a Linux host or for a Windows/Cygwin host:
+
+    tools/configure.sh -c board:configuration
+
+Other options are available from the help option built into the
+script.  You can see all options with:
+
+    tools/configure.sh -h
+
+## Comparing Two Configurations
+
+If you try to compare two configurations using 'diff', you will probably
+not be happy with the result.  There are superfluous things added to
+the configuration files that make comparisons with the human eye
+difficult.
+
+There is a tool at nuttx/tools/cmpconfig.c that can be built to simplify
+these comparisons.  The output from this difference tool will show only
+the meaningful differences between two configuration files.  This tool is
+built as follows:
+
+    cd nuttx/tools
+    make -f Makefile.host
+
+This will create a program called 'cmpconfig' or 'comconfig.exe' on Windows.
+
+Why would you want to compare two configuration files?  Here are a few
+of the reasons why I do this
+
+  1. When I create a new configuration I usually base it on an older
+     configuration and I want to know, "What are the options that I need to
+     change to add the new feature to the older configurations?"  For example,
+     suppose that I have a boardA/nsh configuration and I want to create a
+     boardA/nxwm configuration.  Suppose I already have boardB/nsh and
+     boardB/nxwm configurations.  Then by comparing the boardB/nsh with the
+     boardB/nxwm I can see the modifications that I would need to make to my
+     boardA/nsh to create a new  boardA/nxwm.
+  
+  2. But the most common reason that I use the 'cmpconfig' program is to
+     check the results of "refreshing" a configuration with 'make oldconfig'
+     (see the paragraph "Refreshing Configurations" above).  The 'make
+     oldconfig' command will make changes to my configuration and using
+     'cmpconfig', I can see precisely what those changes were and if any
+     should be of concern to me.
+  
+  3. The 'cmpconfig' tool can also be useful when converting older, legacy
+     manual configurations to the current configurations based on the
+     kconfig-frontends tools.  See the following paragraph.
+
+## Making defconfig Files
+
+### .config Files as defconfig Files:
+
+The minimum defconfig file is simply the generated .config file with
+CONFIG_APPS_DIR setting removed or commented out.  That setting provides
+the name and location of the apps/ directory relative to the nuttx build
+directory.  The default is ../apps/, however, the apps directory may be
+any other location and may have a different name.  For example, the name
+of versioned NuttX releases are always in the form apps-xx.yy where xx.yy
+is the version number.
+
+### Finding the apps/ Directory Path:
+
+When the default configuration is installed using one of the scripts or
+programs in the NuttX tools directory, there will be an option to provide
+the path to the apps/ directory.  If not provided, then the configure tool
+will look around and try to make a reasonable decision about where the
+apps/ directory is located.
+
+### Compressed defconfig Files:
+
+The Makefile also supports an option to generate very small defconfig
+files.  The .config files are quite large and complex.  But most of the
+settings in the .config file simply have the default settings from the
+Kconfig files.  These .config files can be converted into small defconfig
+file:
+    
+    make savedefconfig
+    
+That make target will generate a defconfig file in the top-level
+directory.  The size reduction is really quite remarkable:
+    
+    wc -l .config defconfig
+     1085 .config
+       82 defconfig
+     1167 total
+    
+In order to be usable, the .config file installed from the compressed
+defconfig file must be reconstituted using:
+    
+    make olddefconfig
+    
+  > **NOTE 1**:  Only compressed defconfig files are retained in the NuttX repository.
+  > All patches and PRs that attempt to add or modify a defconfig file MUST
+  > use the compressed defconfig format as created by 'make savdefconfig.'
+    
+  > **NOTE 2**:  When 'make savedefconfig' runs it will try several things some of
+  > which are expected to fail.  In these cases you will see an error message
+  > from make followed by "(ignored)."  You should also ignore these messages
+    
+**CAUTION**:  This size reduction was accomplished by removing all setting
+from the .config file that were at the default value.  'make olddefconfig'
+can regenerate the original .config file by simply restoring those default
+settings.  The underlying assumption here is, of course, that the default
+settings do not change.  If the default settings change, and they often
+do, then the original .config may not be reproducible.
+
+So if your project requires 100% reproducibility over a long period of
+time, you make want to save the complete .config files vs. the standard,
+compressed defconfig file.
+
+### Configuring with "Compressed" defconfig Files:
+
+As described above defconfig, all NuttX defconfig files are compressed
+using 'make savedeconfig'.  These compressed defconfig files are
+generally not fully usable as they are and may not build the target
+binaries that you want because the compression process removed all of
+the default settings from the defconfig file.  To restore the default
+settings, you should run the following after configuring:
+
+    make olddefconfig
+
+That will restore the the missing defaulted values.
+
+Using this command after configuring is generally a good practice anyway:
+Even if the defconfig files are not "compressed" in this fashion, the
+defconfig file may be old and the only way to assure that the installed
+.config is is up to date is via 'make oldconfig' or 'make olddefconfig'.
+See the paragraph above entitled ""Refreshing Configurations" for
+additional information.
+
+## Incompatibilities with Older Configurations
+
+**WARNING**
+
+The current NuttX build system supports *only* the new compressed,
+defconfig configuration files generated using the kconfig-frontends tools
+as described in the preceding section.  Support for the older, legacy,
+manual configurations was eliminated in NuttX 7.0; support for
+uncompressed .config-files-as-defconfig files was eliminated after
+NuttX-7.21.  All configurations must now be done using the
+kconfig-frontends tool.  The older manual configurations and the new
+kconfig-frontends configurations are not compatible.  Old legacy
+configurations can *not* be used with the kconfig-frontends tool and,
+hence, cannot be used with releases of NuttX 7.0 and beyond:
+
+If you run 'make menuconfig' with a legacy configuration the resulting
+configuration will probably not be functional.
+
+  > Q: How can I tell if a configuration is a new kconfig-frontends
+  >   configuration or an older, manual configuration?
+  >
+  > A: Only old, manual configurations will have an appconfig file
+  > 
+  > Q: How can I convert a older, manual configuration into a new,
+  >    kconfig-frontends toolchain.
+  >
+  > A: Refer to <http://www.nuttx.org/doku.php?id=wiki:howtos:convertconfig>
+  
+**WARNING**
+
+As described above, whenever you use a configuration, you really should
+always refresh the configuration with the following command *before* you
+make NuttX:
+
+    make oldconfig
+
+OR
+
+    make olddefconfig
+
+This will make sure that the configuration is up-to-date in the event that
+it has lapsed behind the current NuttX development (see the paragraph
+"Refreshing Configurations" above).  But this only works with *new*
+configuration files created with the kconfig-frontends tools.
+
+Further, this step is *NOT* optional with the new, compressed defconfig
+files.  It is a necessary step that will also uncompress the defconfig
+file, regenerating the .config and making it usable for NuttX builds.
+
+Never do `make oldconfig` (OR `make menuconfig`) on a  configuration that
+has not been converted to use the kconfig-frontends tools!  This will
+damage your configuration (see
+<http://www.nuttx.org/doku.php?id=wiki:howtos:convertconfig>).
+
+## NuttX Configuration Tool under DOS
+
+  Recent versions of NuttX support building NuttX from a native Windows
+  console window (see *Native Windows Build* below).  But kconfig-frontends
+  is a Linux tool.  At one time this was a problem for Windows users, but
+  now there are two specially modified versions of the kconfig-frontends
+  tools that can be used.  One can be found here:
+  <http://uvc.de/posts/linux-kernel-configuration-tool-kconfig-under-windows.html>
+
+  The configuration steps of the most recent versions of NuttX require the
+  kconfig-tweak tool that is not not available in the the above.  However,
+  there has been an update to this Kconfig Windows tools that does include
+  kconfig-tweak:  http://reclonelabs.com/more-kconfig-awesomeness-for-windows/
+
+  Source code is available here: <https://github.com/reclone/kconfig-frontends-win32>
+  and <https://github.com/reclone/kconfig-frontends-win32/releases>
+
+  It is also possible to use the version of kconfig-frontends built
+  under Cygwin outside of the Cygwin "sandbox" in a native Windows
+  environment:
+
+  1. You can run the configuration tool using Cygwin.  However, the
+     Cygwin Makefile.win will complain so to do this will, you have
+     to manually edit the .config file:
+     
+     a. Delete the line: CONFIG_WINDOWS_NATIVE=y
+     
+     b. Change the apps/ directory path, CONFIG_APPS_DIR to use Unix

Review comment:
       ```suggestion
        b. Change the apps/ directory path, `CONFIG_APPS_DIR` to use Unix
   ```

##########
File path: README.md
##########
@@ -0,0 +1,2513 @@
+# APACHE NUTTX (INCUBATING)
+
+* Introduction
+  - Incubation Status
+* Community
+  - Getting Help
+  - Mailing Lists
+  - Issue Tracker
+  - Source Code
+  - Website Source Code
+* Environments
+  - Installing Cygwin
+  - Ubuntu Bash under Windows 10
+  - Using macOS
+* Installation
+  - Download and Unpack
+  - Semi-Optional apps/ Package
+  - Installation Directories with Spaces in the Path
+  - Downloading from Repositories
+  - Related Repositories
+  - Notes about Header Files
+* Configuring NuttX
+  - Instantiating "Canned" Configurations
+  - Refreshing Configurations
+  - NuttX Configuration Tool
+  - Finding Selections in the Configuration Menus
+  - Reveal Hidden Configuration Options
+  - Make Sure that You are on the Right Platform
+  - Comparing Two Configurations
+  - Making defconfig Files
+  - Incompatibilities with Older Configurations
+  - NuttX Configuration Tool under DOS
+* Toolchains
+  - Cross-Development Toolchains
+  - NuttX Buildroot Toolchain
+* Shells
+* Building NuttX
+  - Building
+  - Re-building
+  - Build Targets and Options
+  - Native Windows Build
+  - Installing GNUWin32
+* Cygwin Build Problems
+  - Strange Path Problems
+  - Window Native Toolchain Issues
+* Documentation
+
+# INTRODUCTION
+
+Apache NuttX (Incubating) is a real-time operating system (RTOS) with an
+emphasis on standards compliance and small footprint.  Scalable from 8-bit
+to 32-bit microcontroller environments, the primary governing standards in
+NuttX are POSIX and ANSI standards. Additional standard APIs from Unix and
+other common RTOSs (such as VxWorks) are adopted for functionality not
+available under these standards, or for functionality that is not
+appropriate for deeply-embedded environments (such as fork()).
+
+Extensive documentation can be found on the project wiki:
+  <https://cwiki.apache.org/NUTTX/Nuttx>
+
+## Incubation Status
+
+Apache NuttX (Incubating) is an effort undergoing Incubation at The Apache
+Software Foundation (ASF), sponsored by the Incubator.  For more on our
+incubation effort, please see the file DISCLAIMER-WIP, in the same
+directory as this README.
+
+For brevity, the rest of this file will refer to it as Apache NuttX or
+simply NuttX.
+
+# COMMUNITY
+
+Every volunteer project obtains its strength from the people involved in
+it.  We invite you to participate as much or as little as you choose.
+
+We encourage you to:
+
+  - Use our project and provide feedback.
+  - Provide us with use-cases.
+  - Report bugs and submit patches.
+  - Contribute code or documentation.
+
+## Getting Help
+
+The best place to get help is the developer's mailing list.  Please see
+the following section:
+
+## Mailing Lists
+
+Get help using NuttX or contribute to the project on our mailing lists:
+
+  * <de...@nuttx.apache.org> is for people who want to contribute code to NuttX.
+    * To subscribe, send an email to <de...@nuttx.apache.org>.
+    * To unsubscribe, send an email to <de...@nuttx.apache.org>.
+    * View the archives at:
+      <https://www.mail-archive.com/dev@nuttx.apache.org/>
+
+  * <co...@nuttx.apache.org> is a read-only list that notifies subscribers
+  about commit messages and patches to NuttX.
+    * To subscribe, send an email to <co...@nuttx.apache.org>.
+    * To unsubscribe, send an email to <co...@nuttx.apache.org>.
+    * View the archives at:
+      <https://www.mail-archive.com/commits@nuttx.apache.org/>
+
+## Issue Tracker
+
+### Bug Reports:
+
+Found bug? Send an email to the dev list: <de...@nuttx.apache.org>
+
+Before submitting an issue, please:
+
+  - Verify that the bug does in fact exist. 
+  
+  - Search the mailing list archives to verify there is no existing issue
+    reporting the bug you've found.
+ 
+  - Consider tracking down the bug yourself in the NuttX source code and
+    submitting a patch along with your bug report.  This is a great time
+    saver for the NuttX developers and helps ensure the bug will be fixed
+    quickly.
+  
+### Feature Requests:
+  
+Enhancement requests for new features are also welcome. The more concrete
+and rational the request is, the greater the chance it will incorporated
+into future releases.
+
+## Source Code
+
+The project sources are in two Git repositories.  The core OS is in
+incubator-nuttx and the apps repository is in incubator-nuttx-apps.  These
+are housed in GitBox on ASF servers and also mirrored at GitHub.  These
+are kept in sync, so you can use whichever option you prefer.
+
+  - NuttX core OS repository:
+    
+    - Primary:
+      <https://gitbox.apache.org/repos/asf?p=incubator-nuttx.git>
+    
+    - GitHub Mirror:
+      <https://github.com/apache/incubator-nuttx>
+  
+  - Apps repository:
+    
+    - Primary:
+      <https://gitbox.apache.org/repos/asf?p=incubator-nuttx-apps.git>
+    
+    - GitHub Mirror:
+      <https://github.com/apache/incubator-nuttx-apps>
+
+## Website Source Code
+
+The project website sources are accessible via the website source code
+  repository which is also mirrored in GitHub:
+
+- Primary:
+  <https://gitbox.apache.org/repos/asf?p=incubator-nuttx-website.git>
+
+- GitHub Mirror:
+  <https://github.com/apache/incubator-nuttx-website>
+
+# ENVIRONMENTS
+
+  NuttX requires a POSIX development environment such as you would find under
+  Linux or macOS.  NuttX may also be installed and built on Windows system
+  if you also provide such a POSIX development environment.  Options for a
+  POSIX development environment under Windows include:
+
+  - An installation of Linux on a virtual machine (VM) in Windows.  I have
+    not been happy using a VM myself.  I have had stability problems with
+    open source VMs and commercial VMs cost more than I want to spend.
+    Sharing files with Linux running in a VM is awkward;  sharing devices
+    connected to the Windows box with Linux in a VM is, at the very least,
+    confusing;  Using Windows tools (such as Segger J-Link) with files
+    built under the Linux VM is not a possibility.
+
+  - The Cygwin environment.  Instructions for installation of Cygwin on a
+    Windows system are provided in the following paragraph, "Installing
+    Cygwin".  Cygwin is a mature, well-tested, and very convenient
+    environment.  It is especially convenient if you  need to
+    integrate with Windows tools and files.  Downsides are that the
+    installation time is very long and the compile times are slow.
+
+  - Ubuntu/Bash shell under Windows 10.  This is a new option under
+    Windows 10.  See the section "Ubuntu Bash under Windows 10" below.
+    This is an improvement over Cygwin if your concern is compile time;
+    its build performance is comparable to native Linux, certainly better
+    than the Cygwin build time.  It also installs in a tiny fraction of
+    the time as Cygwin, perhaps 20 minutes for the basic Ubuntu install
+    (vs. more than a day for the complete Cygwin install).
+  
+    There have been even more recent ports of Linux environment to
+    Windows.  I need to update this section to include some mention of
+    these alternatives.
+
+  - The MSYS environment.  MSYS derives from an older version of Cygwin
+    simplified and adapted to work more naturally in the Windows
+    environment.  See <http://www.mingw.org/wiki/MSYS> if you are
+    interested in using MSYS.  The advantages of the MSYS environment is
+    that it is better integrted with the native Windows environment and
+    lighter weight; it uses only a  minimal number of add-on POSIX-land
+    tools.
+  
+    The download link in that Wiki takes you to the SourceForge download
+    site.  The SourceForge MSYS project has been stagnant for some time.
+    The MSYS project has more recently moved to
+    <http://odsn.net/projects/sfnet_mingwbundle>.  Downloads of current .zip
+    files are available there but no instructions for the installation.
+
+  - MSYS2 appears to be a re-write of MSYS based on a newer version of
+    Cygwin.  Is it available at <https://www.msys2.org>.  A windows
+    installer is available at that site along with very good installation
+    instructions.  The download is relatively quick (at least compared to
+    Cygwin) and the 'pacman' package management tool supports supports
+    simple system updates.  For example, 'pacman -S git' will install the
+    GIT command line utilities.
+
+  - Other POSIX environments.  Check out:
+    
+    - UnxUtils: <https://sourceforge.net/projects/unxutils/>,
+      <https://en.wikipedia.org/wiki/UnxUtils>
+    - MobaXterm: <https://mobaxterm.mobatek.net/>
+    - Gow: <https://github.com/bmatzelle/gow/wiki>
+  
+    **Disclaimer**:  In principle, these should work.  However, I have never
+    used any of these environments and cannot guarantee that there is
+    not some less-than-obvious issues.
+  
+NuttX can also be installed and built on a native Windows system, but with
+some potential tool-related issues (see the discussion "Native Windows
+Build" under "Building NuttX" below).  GNUWin32 is used to provide
+compatible native windows tools.
+
+## Installing Cygwin
+
+Installing Cygwin on your Windows PC is simple, but time consuming.  See
+<http://www.cygwin.com/> for installation instructions. Basically you just
+need to download a tiny setup.exe program and it does the real, network
+installation for you.
+
+Some Cygwin installation tips:
+
+  1. Install at `C:\cygwin`
+  
+  2. Install **everything**:  "Only the minimal base packages from the
+     Cygwin distribution are installed by default. Clicking on categories
+     and packages in the setup.exe package installation screen will
+     provide you with the ability to control what is installed or updated.
+     Clicking on the "Default" field next to the "All" category will
+     provide you with the opportunity to install every Cygwin package.
+     Be advised that this will download and install hundreds of megabytes
+     to your computer."
+   
+If you use the "default" installation, you will be missing many
+of the Cygwin utilities that you will need to build NuttX.  The
+build will fail in numerous places because of missing packages.
+
+NOTE: The last time I installed **everything**, the download was
+about 5GiB.  The server I selected was also very slow so it took
+over a day to do the whole install!
+
+NOTE: You don't really have to install **everything** but I cannot
+answer the question "Then what should I install?"  I don't know
+the answer to that and so will continue to recommend installing
+**everything**.
+
+You should certainly be able to omit "Science", "Math", and
+"Publishing".  You can try omitting KDE, Gnome, GTK, and other
+graphics packages if you don't plan to use them.
+
+Perhaps a minimum set would be those packages listed below for the
+"Ubuntu Bash under Windows 10" installation?
+
+**UPDATE**:  Sergey Frolov had success with the following minimal
+Cygwin configuration:
+   
+   1. After starting the Cygwin installer, keep the recommended
+      packages that are pre-selected in the default configuration.
+   
+   2. Using the installation tools, add the following packages:
+      
+        make (GNU make)  bison        libgmp3-dev
+        gcc-core         byacc        libmpfr-dev
+        gcc-g++          gperf        libmpc-dev
+        flex             gdb          automake-1.15
+        libncurses-dev   libgmp-dev
+   
+After installing Cygwin, you will get lots of links for installed
+tools and shells.  I use the RXVT native shell.  It is fast and reliable
+and does not require you to run the Cygwin X server (which is neither
+fast nor reliable).  Unless otherwise noted, the rest of these
+instructions assume that you are at a bash command line prompt in
+either Linux or in Cygwin shell.
+
+## Using MSYS
+
+MSYS is an environment the derives from Cygwin.  Thus, most things said
+about Cygwin apply equally to MSYS.  This section will, then, focus on
+the differences when using MSYS, specifically MSYS2.
+
+Here is it assumed that you have already downloaded and installed MSYS2
+from https://www.msys2.org using the windows installer available at that
+location.  It is also assumed that you have brought in the necessary
+tools using the 'pacman' package management tool Tools needed including:
+
+  pacman -S git
+  pacman -S make
+  pacman -S gcc
+  pacman -S gdb
+
+And possibly others depending upon your usage.  Then you will need to
+build and install kconfig-frontends per the instructions of the top-level
+README.txt file in the tools repository.  This requires the following
+additional tools:
+
+    pacman -S bison
+    pacman -S gperf
+    pacman -S ncurses-devel
+    pacman -S automake-wrapper
+    pacman -S autoconf
+    pacman -S pkg-config
+
+Because of some versioning issues, I had to run 'aclocal' prior to
+running the kconfig-frontends configure script.  See "Configuring NuttX"
+below for further information.
+
+Unlike Cygwin, MSYS does not support symbolic links.  The 'ln -s' command
+will, in fact, copy a directory!  This means that you Make.defs file will
+have to include definitions like:
+
+    ifeq ($(CONFIG_WINDOWS_MSYS),y)
+      DIRLINK = $(TOPDIR)/tools/copydir.sh
+      DIRUNLINK = $(TOPDIR)/tools/unlink.sh
+    endif
+
+This will force the directory copies to work in a way that can be handled
+by the NuttX build system.  NOTE:  The default link.sh script has been
+updated so that is should now be MSYS2 compatible.  The above is preferred
+but no longer necessary in the Make.defs file.
+
+To build the simulator under MSYS, you also need:
+
+    pacman -S zlib-devel
+
+It appears that you cannot use directory names with spaces in them like
+"/c/Program\ Files \(86\)" in the MSYS path variable.  I worked around this
+by create Windows junctions like this:
+
+  1. Open the a windows command terminal,
+  
+  2. CD to `c:\msys64`, then
+  
+  3. `mklink /j programfiles "C:/Program\ Files"` and
+  
+  4. `mklink /j programfiles86 "C:/Program\ Files\ \(x86\)"`
+     
+     They then show up as `/programfiles` and `/programfiles86` with the MSYS2
+     sandbox.  Those paths can then be used with the PATH variable.  I had
+     to do something similar for the path to the GNU Tools "ARM Embedded
+     Toolchain" which also has spaces in the path name.
+
+## Ubuntu Bash under Windows 10
+
+A better version of a command-line only Ubuntu under Windows 10 (beta)
+has recently been made available from Microsoft.
+
+### Installation
+
+Installation instructions abound on the Internet complete with screen
+shots.  I will attempt to duplicate those instructions in full here.
+Here are the simplified installation steps:
+
+  - Open *Settings*.
+  
+  - Click on *Update & security*.
+  
+  - Click on *For Developers*.
+  
+  - Under *Use developer features*, select the *Developer mode* option to
+    setup the environment to install Bash.
+  
+  - A message box should pop up.  Click *Yes* to turn on developer mode.
+  
+  - After the necessary components install, you'll need to restart your
+    computer.
+    
+    Once your computer reboots:
+  
+  - Open *Control Panel*.
+  
+  - Click on *Programs*.
+  
+  - Click on *Turn Windows features on or off*.
+  
+  - A list of features will pop up, check the *Windows Subsystem for Linux
+    (beta)* option.
+  
+  - Click *OK*.
+  
+  - Once the components installed on your computer, click the *Restart
+    now* button to complete the task.
+    
+    After your computer restarts, you will notice that Bash will not appear in
+    the *Recently added* list of apps, this is because Bash isn't actually
+    installed yet. Now that you have setup the necessary components, use the
+    following steps to complete the installation of Bash:
+  
+  - Open *Start*, do a search for `bash.exe`, and press *Enter*.
+  
+  - On the command prompt, type `y` and press Enter to download and install
+    Bash from the Windows Store.  This will take awhile.
+  
+  - Then you'll need to create a default UNIX user account. This account
+    doesn't have to be the same as your Windows account. Enter the
+    username in the required field and press Enter (you can't use the
+    username `admin`).
+  
+  - Close the `bash.exe` command prompt.
+  
+  Now that you completed the installation and setup, you can open the Bash
+  tool from the Start menu like you would with any other app.
+
+### Accessing Windows Files from Ubuntu
+
+File systems will be mounted under `/mnt` so for example `C:\Program Files`
+appears at `/mnt/c/Program Files`.  This is as opposed to Cygwin where
+the same directory would appear at `/cygdrive/c/Program Files`.
+
+With these differences (perhaps a few other Windows quirks) the Ubuntu
+install works just like Ubuntu running natively on your PC.
+
+A good tip for file sharing is to use symbolic links within your Ubuntu
+home directory.  For example, suppose you have your `projects` directory
+at `C:\Documents\projects`.  Then you can set up a link to the `projects/`
+directory in your Ubuntu directory like:
+
+    ln -s /mnt/c/Documents/projects projects
+
+### Accessing Ubuntu Files From Windows
+
+In Ubuntu Userspace for Windows, the Ubuntu file system root directory is
+at:
+
+    %localappdata%\lxss\rootfs
+
+Or
+
+    C:\Users\Username\AppData\Local\lxss\rootfs
+
+However, I am unable to see my files under the rootfs\home directory.
+After some looking around, I find the home directory
+`%localappdata%\lxss\home`.
+
+With that trick access to the `/home` directory, you should actually be
+able to use Windows tools outside of the Ubuntu sandbox with versions of
+NuttX built within the sandbox using that path.
+
+### Executing Windows Tools from Ubuntu
+
+You can also execute Windows tools from within the Ubuntu sandbox:
+
+    /mnt/c/Program\ Files\ \(x86\)/Microchip/xc32/v1.43/bin/xc32-gcc.exe --version
+    Unable to translate current working directory. Using C:\WINDOWS\System32
+    xc32-gcc.exe (Microchip Technology) 4.8.3 MPLAB XC32 Compiler v1.43 Build date: Mar  1 2017
+    ...
+
+The error message indicates that there are more issues:  You cannot mix
+Windows tools that use Windows style paths in an environment that uses
+POSIX paths.  I think you would have to use Linux tools only from within
+the Ubuntu sandbox.
+
+### Install Ubuntu Software
+
+Use `sudo apt-get install <package name>`.  As examples, this is how
+you would get GIT:
+
+    sudo apt-get install git
+
+This will get you a compiler for your host PC:
+
+    sudo apt-get install gcc
+
+This will get you an ARM compiler for your target:
+
+    sudo apt-get install gcc-arm-none-eabi
+
+**NOTE**: That is just an example.  I am not sure if apt-get will give you a
+current or usable compiler.  You should carefully select your toolchain
+for the needs of your project.
+
+You will also need to get the kconfig-frontends configuration as
+described below under *NuttX Configuration Tool*.  In order to build the
+kconfig-frontends configuration tool you will also need: `make`, `gperf`,
+`flex`, `bison`, and `libncurses-dev`.
+
+That is enough to do a basic NuttX build.
+
+### Integrating with Windows Tools
+
+If you want to integrate with Windows native tools, then you would need
+deal with the same kind of craziness as with integrating Cygwin with
+native toolchains, see the section *Cygwin Build Problems* below.
+
+However, there is currently no build support for using Windows native
+tools with Ubuntu under Windows.  This tool combination is made to work
+with Cygwin through the use of the `cygpath -w` tool that converts paths
+from say `/cydrive/c/Program Files` to `C:\Program Files`.  There is,
+however, no corresponding tool to convert `/mnt/c/Program Files` in the
+Ubuntu environment.
+
+### Graphics Support
+
+The Ubuntu version support by Microsoft is a command-line only version.
+There is no support for Linux graphics utilities.
+
+This limitation is not a limitation of Ubuntu, however, only in what
+Microsoft is willing to support.  If you install a X-Server, then you
+can also use basic graphics utilities.  See for example:
+
+  <http://www.howtogeek.com/261575/how-to-run-graphical-linux-desktop-applications-from-windows-10s-bash-shell/>
+
+Many Linux graphics programs would, however, also require a graphics
+framework like GTK or Qt.  So this might be a trip down the rabbit hole.
+
+### Using macOS
+
+You need to install at least the following tools specific to macOS.
+
+  * flock (used by APPDIR build logic)
+    
+A macOS port is available at: <https://github.com/discoteq/flock>
+  
+    brew tap discoteq/discoteq
+    brew install flock
+  
+  If you want to build the sim:
+
+  * Xcode (the native compiler and the rest of the toolchain)
+
+  * ELF toolchain (if you want to build modules for CONFIG_LIBC_MODLIB)
+
+    brew install x86_64-elf-gc
+
+# INSTALLATION
+
+There are two ways to get NuttX:  You may download released, stable
+tarballs from either the project website.  Or you may get NuttX by
+cloning the GIT repositories.  Let's consider the released tarballs
+first:
+
+## Download and Unpack
+
+Download and unpack the NuttX tarball.  If you are reading this, then
+you have probably already done that.  After unpacking, you will end
+up with a directory called nuttx-version (where version is the NuttX
+version number). You might want to rename that directory nuttx to
+match the various instructions in the documentation and some scripts
+in the source tree.
+
+  * Download location:
+  
+    <https://nuttx.apache.org/download/>
+  
+  * Legacy download locations:
+
+    <https://bitbucket.org/nuttx/nuttx/downloads>  
+    <https://sourceforge.net/projects/nuttx/files/nuttx/>
+
+## Semi-Optional apps/ Package
+
+All NuttX libraries and example code used to be in included within
+the NuttX source tree.  As of NuttX-6.0, this application code was
+moved into a separate tarball, the apps tarball.  If you are just
+beginning with NuttX, then you will want to download the versioned
+apps tarball along with the NuttX tarball.  If you already have your
+own product application directory, then you may not need the apps
+tarball.
+
+It is called "Semi-optional" because if you don't have some `apps/`
+directory, NuttX will *fail* to build! You do not necessarily need
+to use the NuttX apps tarball but may, instead, provide your own
+custom application directory.  Such a custom directory would need
+to include a valid Makefile to support the build and a valid Kconfig
+file to support the configuration.  More about these files later.
+
+Download then unpack the apps tarball in the same directory where you
+unpacked the NuttX tarball.  After you unpack the apps tarball, you
+will have a new directory called apps-version (where the version
+should exactly match the version of the NuttX tarball).  Again, you
+might want to rename the directory to simply apps/ to match what
+you read in the documentation
+
+After unpacking (and renaming) the apps tarball, you will have two
+directories side by side like this:
+
+             |
+        +----+----+
+        |         |
+      nuttx/     apps/
+
+This is important because the NuttX build will expect to find the
+apps directory in that (default) location.  That default location
+can be changed by modifying your NuttX configuration file, but that
+is another story.
+
+## Installation Directories with Spaces in the Path
+
+The nuttx build directory should reside in a path that contains no
+spaces in any higher level directory name.  For example, under
+Cygwin, your home directory might be formed from your first and last
+names like: `/home/First Last`. That will cause strange errors when
+the make system tries to build.
+
+[Actually, that problem is probably not too difficult to fix.  Some
+ Makefiles probably just need some paths within double quotes]
+
+I work around spaces in the home directory name, by creating a
+new directory that does not contain any spaces, such as `/home/nuttx`.
+Then I install NuttX in `/home/nuttx` and always build from
+`/home/nuttx/nuttx-code`.
+
+## Downloading from Repositories
+
+### Cloning the Repository
+
+**BEFORE** cloning repositories on any Windows platform do the following GIT
+command:
+
+    git config --global core.autocrlf false
+
+That will avoid conversions of linefeeds (newlines, \n) to carriage
+return plus linefeed sequences (\r\n)
+
+The current NuttX du jour is available in from a GIT repository.  Here are
+instructions for cloning the core NuttX RTOS (corresponding to the nuttx
+tarball discussed above):
+
+    git clone https://gitbox.apache.org/repos/asf/incubator-nuttx.git nuttx
+
+-or-
+
+    git clone https://github.com/apache/incubator-nuttx.git nuttx
+
+And the semi-optional apps/ application directory and be cloned like:
+
+    git clone https://gitbox.apache.org/repos/asf/incubator-nuttx-apps.git apps
+  
+-or-
+  
+    git clone https://github.com/apache/incubator-nuttx-apps.git apps
+
+That will give you the same directory structure like this:
+    
+             |
+        +----+----+
+        |         |
+      nuttx/     apps/
+
+### Configuring the Clones
+
+The following steps need to be performed for each of the repositories.
+After changing to the clone directory:
+
+Set your identity:
+
+    git config --global user.name "My Name"
+    git config --global user.email my.name@example.com
+  
+Colorized diffs are much easier to read:
+
+    git config --global color.branch auto
+    git config --global color.diff auto
+    git config --global color.interactive auto
+    git config --global color.status auto
+
+Checkout other settings
+
+    git config --list
+
+### Cloning NuttX Inside Cygwin
+
+If you are cloning the NuttX repository, it is recommended to avoid
+automatic end of lines conversions by git. These conversions may break
+some scripts like configure.sh. Before cloning, do the following:
+
+    git config --global core.autocrlf false
+
+## Related Repositories
+
+These are standalone repositories:
+
+  * <https://gitbox.apache.org/repos/asf/incubator-nuttx-apps>  
+    or  
+    <https://github.com/apache/incubator-nuttx-apps.git>
+    
+    This directory holds an optional package of applications and libraries
+    can be used with the NuttX RTOS.  There is a README.txt file there that
+    will provide more information about that package.
+
+  * <https://bitbucket.org/nuttx/nxwidgets>
+  
+    This is the NuttX C++ graphics support.  This includes NxWM, the tiny
+    NuttX Window Manager.
+
+  * <https://bitbucket.org/nuttx/uclibc>
+  
+    This repository contains a version of the uClibc++ C++ library.  This code
+    originates from <http://cxx.uclibc.org/> and has been adapted for NuttX by the
+    RGMP team (<http://rgmp.sourceforge.net/wiki/index.php/Main_Page>).
+
+  * <https://bitbucket.org/nuttx/buildroot>
+  
+    A environment that you can to use to build a custom, NuttX GNU toolchain.
+
+  * <https://bitbucket.org/nuttx/tools>
+  
+    There are snapshots of some tools here that you will need to work with
+    NuttX:  kconfig-frontends, genromfs, and others.
+
+## Notes about Header Files
+
+### Other C-Library Header Files
+
+When a GCC toolchain is built, it must be built against a C library.
+The compiler together with the contents of the C library completes the
+C language definition and provides the complete C development
+environment.  NuttX provides its own, built-in C library.  So the
+complete, consistent C language definition for use with NuttX comes from
+the combination of the compiler and the header files provided by the
+NuttX C library.
+
+When a GCC toolchain is built, it incorporates the C library header
+files into the compiler internal directories and, in this way, the C
+library really becomes a part of the toolchain.  If you use the NuttX
+buildroot toolchain as described below under "NuttX Buildroot
+Toolchain", your GCC toolchain will build against the NuttX C library
+and will incorporate the NuttX C library header files as part of the
+toolchain.
+
+If you use some other, third-party tool chain, this will not be the
+case, however.  Those toolchains were probably built against some
+other, incompatible C library distribution (such as newlib).  Those
+tools will have incorporated the incompatible C library header files
+as part of the toolchain.  These incompatible header files must *not*
+be used with NuttX because they will conflict with definitions in the
+NuttX built-in C-Library.  For such toolchains that include header
+files from a foreign C-Library, NuttX must be compiled without using
+the standard header files that are distributed with your toolchain.
+This prevents including conflicting, incompatible header files such
+as stdio.h.
+
+The math.h and stdarg.h are probably the two most trouble some header
+files to deal with.  These troublesome header files are discussed in
+more detail below.
+
+### Header Files Provided by Your Toolchain
+
+Certain header files, such as `setjmp.h`, `stdarg.h`, and `math.h`, may still
+be needed from your toolchain and your compiler may not, however, be able
+to find these if you compile NuttX without using standard header files
+(i.e., with `-nostdinc`).  If that is the case, one solution is to copy
+those header file from your toolchain into the NuttX include directory.
+
+### Duplicated Header Files
+
+There are also a few header files that can be found in the `nuttx/include`
+directory which are duplicated by the header files from your toolchain.
+stdint.h and stdbool.h are examples.  If you prefer to use the `stdint.h`
+and `stdbool.h` header files from your toolchain, those could be copied
+into the `nuttx/include/` directory. Using most other header files from
+your toolchain would probably cause errors.
+
+### math.h
+
+Even though you should not use a foreign C-Library, you may still need
+to use other, external libraries with NuttX.  In particular, you may
+need to use the math library, libm.a.  NuttX supports a generic, built-in
+math library that can be enabled using `CONFIG_LIBM=y`.  However, you may
+still want to use a higher performance external math library that has
+been tuned for your CPU.  Sometimes such tuned math libraries are
+bundled with your toolchain.
+
+The math library header file, `math.h`, is a then special case.  If you do
+nothing, the standard math.h header file that is provided with your
+toolchain will be used.
+
+If you have a custom, architecture specific math.h header file, then
+that header file should be placed at `arch/<cpu>/include/math.h`.  There
+is a stub `math.h` header file located at `include/nuttx/lib/math.h`.  This stub
+header file can be used to "redirect" the inclusion to an architecture-
+specific math.h header file.  If you add an architecture specific math.h
+header file then you should also define `CONFIG_ARCH_MATH_H=y` in your
+NuttX Configuration file.  If `CONFIG_ARCH_MATH_H` is selected, then the
+top-level Makefile will copy the stub math.h header file from
+`include/nuttx/lib/math.h` to `include/math.h` where it will become the system
+`math.h` header file.  The stub `math.h` header file does nothing other
+than to include that architecture-specific `math.h` header file as the
+system `math.h` header file.
+
+### float.h
+
+If you enable the generic, built-in math library, then that math library
+will expect your toolchain to provide the standard `float.h` header file.
+The float.h header file defines the properties of your floating point
+implementation.  It would always be best to use your toolchain's `float.h`
+header file but if none is available, a default `float.h` header file will
+be provided if this option is selected.  However, there is no assurance
+that the settings in this `float.h` are actually correct for your platform!
+
+### stdarg.h
+
+In most cases, the correct version of stdarg.h is the version provided
+with your toolchain.  However, sometimes there are issues with
+using your toolchains `stdarg.h`.  For example, it may attempt to draw in
+header files that do not exist in NuttX or perhaps the header files that
+it uses are not compatible with the NuttX header files.  In those cases,
+you can use an architecture-specific `stdarg.h` header file by defining
+`CONFIG_ARCH_STDARG_H=y`.
+
+See the discussion above for the `math.h` header.  This setting works
+exactly the same for the `stdarg.h` header file.
+
+# CONFIGURING NUTTX
+
+## Instantiating "Canned" Configurations
+
+### `configure.sh` and `configure.bat`
+
+"Canned" NuttX configuration files are retained in:
+
+    boards/<arch-name>/<chip-name>/<board-name>/configs/<config-dir>
+
+Where `<board-name>` is the name of your development board and `<config-dir>`
+is the name of the sub-directory containing a specific configuration for
+that board. `<arch-name>` and `<chip-name>` refer to characteristics of the
+MCU used on the board: `<arch-name>` is the CPU architecture implemented
+by the MCU; `<chip-name>` identifies the MCU chip family.  Only a few
+steps are required to instantiate a NuttX configuration, but to make the
+configuration even easier there are scripts available in the tools/
+sub-directory combines those simple steps into one command.
+
+There is one tool for use with any Bash-like shell that does configuration
+steps.  It is used as follows:
+
+    tools/configure.sh <board-name>:<config-dir>
+
+There is an alternative Windows batch file that can be used in the windows
+native environment like:
+
+    tools\configure.bat <board-name>:<config-dir>
+
+And, to make sure that other platforms are supported, there is also a
+C program at tools/configure.c that can be compiled to establish the
+board configuration.
+
+See `tools/README.txt` for more information about these scripts.
+
+General information about configuring NuttX can be found in:
+
+    {TOPDIR}/boards/README.txt
+    {TOPDIR}/boards/<arch-name>/<chip-name>/<board-name>/README.txt
+
+### The Hidden Configuration Scripts:
+
+As mentioned above, there are only a few simple steps to instantiating a
+NuttX configuration.  Those steps are hidden by the configuration scripts
+but are summarized below:
+  
+  1. Copy Files
+  
+     Configuring NuttX requires only copying two files from the
+     `<config-dir>` to the directory where you installed NuttX (TOPDIR):
+  
+       * Copy `boards/<arch-name>/<chip-name>/<board-name>/configs/<config-dir>/Make.def` to `{TOPDIR}/Make.defs`
+    
+         OR
+    
+       * Copy `boards/<arch-name>/<chip-name>/<board-name>/scripts/Make.def`
+         to `{TOPDIR}/Make.defs`
+    
+         Make.defs describes the rules needed by your tool chain to compile
+         and link code.  You may need to modify this file to match the
+         specific needs of your toolchain.  NOTE that a configuration may
+         have its own unique Make.defs file in its configuration directory or
+         it may use a common Make.defs file for the board in the scripts/
+         directory.  The first takes precedence.
+    
+       * Copy `boards/<arch-name>/<chip-name>/<board-name>/configs/<config-dir>/defconfig` to `{TOPDIR}/.config`
+    
+         The defconfig file holds the actual build configuration.  This
+         file is included by all other make files to determine what is
+         included in the build and what is not.  This file is also used
+         to generate a C configuration header at `include/nuttx/config.h`.
+    
+       * Copy other, environment-specific files to `{TOPDIR}`
+    
+         This might include files like .gdbinit or IDE configuration files
+         like .project or .cproject.
+  
+  2. Refresh the Configuration
+  
+     New configuration setting may be added or removed.  Existing settings
+     may also change there values or options.  This must be handled by
+     refreshing the configuration as described below.
+    
+     NOTE:  NuttX uses only compressed defconfig files.  For the NuttX
+     defconfig files, this refreshing step is *NOT* optional; it is also
+     necessary to uncompress and regenerate the full making file.  This is
+     discussed further below.
+
+## Refreshing Configurations
+
+Configurations can get out of date.  As new configuration settings are
+added or removed or as dependencies between configuration settings
+change, the contents of a default configuration can become out of synch
+with the build systems.  Hence, it is a good practice to "refresh" each
+configuration after configuring and before making.  To refresh the
+configuration, use the NuttX Configuration Tool like this:
+
+    make oldconfig
+
+AFTER you have instantiated the NuttX configuration as described above.
+The configuration step copied the .config file into place in the top-level
+NuttX directory; 'make oldconfig' step will then operate on that .config
+file to bring it up-to-date.
+
+If your configuration is out of date, you will be prompted by 'make oldconfig'
+to resolve the issues detected by the configuration tool, that is, to
+provide values for the new configuration options in the build system.  Doing
+this can save you a lot of problems down the road due to obsolete settings in
+the default board configuration file.  The NuttX configuration tool is
+discussed in more detail in the following paragraph.
+
+Confused about what the correct value for a new configuration item should
+be?  Enter ? in response to the 'make oldconfig' prompt and it will show
+you the help text that goes with the option.
+
+If you don't want to make any decisions are willing to just accept the
+recommended default value for each new configuration item, an even easier
+way is:
+
+    make olddefconfig
+
+The olddefconfig target will simply bring your configuration up to date with
+the current Kconfig files, setting any new options to the default value.
+No questions asked.
+
+## NuttX Configuration Tool
+
+An automated tool has been incorporated to support re-configuration
+of NuttX.  This tool is based on the kconfig-frontends application available
+at <https://bitbucket.org/nuttx/tools/src/master/kconfig-frontends/>.  (This
+is a snapshot of the old <http://ymorin.is-a-geek.org/projects/kconfig-frontends>
+which is no longer available.)  This application provides a tool called
+`kconfig-mconf` that is used by the NuttX top-level Makefile. The following
+make target is provided:
+
+    make menuconfig
+
+This make target will bring up NuttX configuration menus.
+
+**WARNING**:  Never do `make menuconfig` on a configuration that has
+not been converted to use the kconfig-frontends tools!  This will
+damage your configuration (see
+<http://www.nuttx.org/doku.php?id=wiki:howtos:convertconfig>).
+
+How do we tell a new configuration from an old one? See "Incompatibilities
+with Older Configurations" below.
+
+The `menuconfig` make target depends on two things:
+
+  1. The Kconfig configuration data files that appear in almost all
+     NuttX directories.  These data files are the part that is still
+     under development (patches are welcome!).  The Kconfig files
+     contain configuration information for the configuration settings
+     relevant to the directory in which the Kconfig file resides.
+     
+     NOTE: For a description of the syntax of this configuration file,
+     see kconfig-language.txt in the tools repository at
+     <https://bitbucket.org/nuttx/tools>
+  
+  2. The `kconfig-mconf` tool. `kconfig-mconf` is part of the
+     kconfig-frontends package.  You can download that package from the
+     snapshot in the tools repository at <https://bitbucket.org/nuttx/tools>.
+  
+     Building kconfig-frontends under Linux may be as simple as
+     `configure; make; make install` but there may be some build
+     complexities, especially if you are building under Cygwin.  See
+     the more detailed build instructions in the top-level README.txt
+     file of the tools repository at <https://bitbucket.org/nuttx/tools>.
+  
+  
+     The `make install` step will, by default, install the `kconfig-mconf`
+     tool at `/usr/local/bin/mconf`.  Where ever you choose to
+     install `kconfig-mconf`, make certain that your PATH variable includes
+     a path to that installation directory.
+  
+     The kconfig-frontends tools will not build in a native Windows
+     environment directly "out-of-the-box".  For the Windows native
+     case, you can use the modified version of kconfig-frontends
+     that can be found at
+
+     <http://uvc.de/posts/linux-kernel-configuration-tool-kconfig-under-windows.html>  
+
+     or a more recent port that can be found at  
+
+     <http://reclonelabs.com/more-kconfig-awesomeness-for-windows/>.
+   
+The basic configuration order is "bottom-up":
+   
+   - Select the build environment,
+   - Select the processor,
+   - Select the board,
+   - Select the supported peripherals
+   - Configure the device drivers,
+   - Configure the application options on top of this.
+   
+This is pretty straight forward for creating new configurations
+but may be less intuitive for modifying existing configurations.
+
+Another ncurses-based tool that is an option to kconfig-mconf is
+kconfig-nconf.  The differences are primary in in the aesthetics of the
+UI.  If you have kconfig-nconf built, then you can invoke that front end
+with:
+   
+     make nconfig
+   
+If you have an environment that supports the Qt or GTK graphical systems
+(probably KDE or gnome, respectively, or Cygwin under Windows with Qt or
+GTK installed), then you can also build the graphical kconfig-frontends,
+kconfig-qconf and kconfig-gconf.  In these case, you can start the
+graphical configurator with either:
+   
+     make qconfig
+   
+ or
+   
+     make gconfig
+   
+Some keyboard shortcuts supported by kconfig-mconf, the tool that runs
+when you do 'make menuconfig':
+
+   - `?` will bring up the mconfig help display.
+   
+   - `/` can be used find configuration selections.
+   
+   - `Z` can be used to reveal hidden configuration options
+   
+These last two shortcuts are described further in the following
+paragraphs.
+
+## Finding Selections in the Configuration Menus
+
+The NuttX configuration options have gotten complex and it can be very
+difficult to find options in the menu trees if you are not sure where
+to look.  The "basic configuration order" describe above can help to
+narrow things down.
+
+But if you know exactly what configuration setting you want to select,
+say CONFIG_XYZ, but not where to find it, then the 'make menuconfig'
+version of the tool offers some help:  By pressing the '/' key, the
+tool will bring up a menu that will allow you to search for a
+configuration item.  Just enter the string CONFIG_XYZ and press 'ENTER'.
+It will show you not only where to find the configuration item, but
+also all of the dependencies related to the configuration item.
+
+## Reveal Hidden Configuration Options
+
+If you type `Z`, then kconfig-mconf will change what is displayed.
+Normally, only enabled features that have all of their dependencies met
+are displayed.  That is, of course, not very useful if you would like to
+discover new options or if you are looking for an option and do not
+realize that the dependencies have not yet been selected and, hence, it
+is not displayed.
+
+But if you enter `Z`, then every option will be shown, whether or not its
+dependencies have been met.  You can then see everything that could be
+selected with the right dependency selections.  These additional options
+will be shown the `-` for the selection and for the value (since it
+cannot be selected and has no value).  About all you do is to select
+the `<Help>` option to see what the dependencies are.
+
+## Make Sure that You are on the Right Platform
+
+Saved configurations may run on Linux, Cygwin (32- or 64-bit), or other
+platforms.  The platform characteristics can be changed use `make
+menuconfig`.  Sometimes this can be confusing due to the differences
+between the platforms.  Enter sethost.sh
+
+sethost.sh is a simple script that changes a configuration to your
+host platform.  This can greatly simplify life if you use many different
+configurations.  For example, if you are running on Linux and you
+configure like this:
+
+    tools/configure.sh board:configuration
+
+The you can use the following command to both (1) make sure that the
+configuration is up to date, AND (2) the configuration is set up
+correctly for Linux:
+
+    tools/sethost.sh -l
+
+Or, if you are on a Windows/Cygwin 64-bit platform:
+
+    tools/sethost.sh -c
+
+Or, for MSYS/MSYS2:
+
+    tools/sethost.sh -g
+
+Other options are available from the help option built into the
+script.  You can see all options with:
+
+    tools/sethost.sh -h
+
+Recently, the options to the configure.sh (and configure.bat) scripts have
+been extended so that you both setup the configuration, select for the host
+platform that you use, and uncompress and refresh the defconfig file all in
+one command like:
+
+    tools/configure.sh -l board:configuration
+
+For a Linux host or for a Windows/Cygwin host:
+
+    tools/configure.sh -c board:configuration
+
+Other options are available from the help option built into the
+script.  You can see all options with:
+
+    tools/configure.sh -h
+
+## Comparing Two Configurations
+
+If you try to compare two configurations using 'diff', you will probably
+not be happy with the result.  There are superfluous things added to
+the configuration files that make comparisons with the human eye
+difficult.
+
+There is a tool at nuttx/tools/cmpconfig.c that can be built to simplify
+these comparisons.  The output from this difference tool will show only
+the meaningful differences between two configuration files.  This tool is
+built as follows:
+
+    cd nuttx/tools
+    make -f Makefile.host
+
+This will create a program called 'cmpconfig' or 'comconfig.exe' on Windows.
+
+Why would you want to compare two configuration files?  Here are a few
+of the reasons why I do this
+
+  1. When I create a new configuration I usually base it on an older
+     configuration and I want to know, "What are the options that I need to
+     change to add the new feature to the older configurations?"  For example,
+     suppose that I have a boardA/nsh configuration and I want to create a
+     boardA/nxwm configuration.  Suppose I already have boardB/nsh and
+     boardB/nxwm configurations.  Then by comparing the boardB/nsh with the
+     boardB/nxwm I can see the modifications that I would need to make to my
+     boardA/nsh to create a new  boardA/nxwm.
+  
+  2. But the most common reason that I use the 'cmpconfig' program is to
+     check the results of "refreshing" a configuration with 'make oldconfig'
+     (see the paragraph "Refreshing Configurations" above).  The 'make
+     oldconfig' command will make changes to my configuration and using
+     'cmpconfig', I can see precisely what those changes were and if any
+     should be of concern to me.
+  
+  3. The 'cmpconfig' tool can also be useful when converting older, legacy
+     manual configurations to the current configurations based on the
+     kconfig-frontends tools.  See the following paragraph.
+
+## Making defconfig Files
+
+### .config Files as defconfig Files:
+
+The minimum defconfig file is simply the generated .config file with
+CONFIG_APPS_DIR setting removed or commented out.  That setting provides
+the name and location of the apps/ directory relative to the nuttx build
+directory.  The default is ../apps/, however, the apps directory may be
+any other location and may have a different name.  For example, the name
+of versioned NuttX releases are always in the form apps-xx.yy where xx.yy
+is the version number.
+
+### Finding the apps/ Directory Path:
+
+When the default configuration is installed using one of the scripts or
+programs in the NuttX tools directory, there will be an option to provide
+the path to the apps/ directory.  If not provided, then the configure tool
+will look around and try to make a reasonable decision about where the
+apps/ directory is located.
+
+### Compressed defconfig Files:
+
+The Makefile also supports an option to generate very small defconfig
+files.  The .config files are quite large and complex.  But most of the
+settings in the .config file simply have the default settings from the
+Kconfig files.  These .config files can be converted into small defconfig
+file:
+    
+    make savedefconfig
+    
+That make target will generate a defconfig file in the top-level
+directory.  The size reduction is really quite remarkable:
+    
+    wc -l .config defconfig
+     1085 .config
+       82 defconfig
+     1167 total
+    
+In order to be usable, the .config file installed from the compressed
+defconfig file must be reconstituted using:
+    
+    make olddefconfig
+    
+  > **NOTE 1**:  Only compressed defconfig files are retained in the NuttX repository.
+  > All patches and PRs that attempt to add or modify a defconfig file MUST
+  > use the compressed defconfig format as created by 'make savdefconfig.'
+    
+  > **NOTE 2**:  When 'make savedefconfig' runs it will try several things some of
+  > which are expected to fail.  In these cases you will see an error message
+  > from make followed by "(ignored)."  You should also ignore these messages
+    
+**CAUTION**:  This size reduction was accomplished by removing all setting
+from the .config file that were at the default value.  'make olddefconfig'
+can regenerate the original .config file by simply restoring those default
+settings.  The underlying assumption here is, of course, that the default
+settings do not change.  If the default settings change, and they often
+do, then the original .config may not be reproducible.
+
+So if your project requires 100% reproducibility over a long period of
+time, you make want to save the complete .config files vs. the standard,
+compressed defconfig file.
+
+### Configuring with "Compressed" defconfig Files:
+
+As described above defconfig, all NuttX defconfig files are compressed
+using 'make savedeconfig'.  These compressed defconfig files are
+generally not fully usable as they are and may not build the target
+binaries that you want because the compression process removed all of
+the default settings from the defconfig file.  To restore the default
+settings, you should run the following after configuring:
+
+    make olddefconfig
+
+That will restore the the missing defaulted values.
+
+Using this command after configuring is generally a good practice anyway:
+Even if the defconfig files are not "compressed" in this fashion, the
+defconfig file may be old and the only way to assure that the installed
+.config is is up to date is via 'make oldconfig' or 'make olddefconfig'.
+See the paragraph above entitled ""Refreshing Configurations" for
+additional information.
+
+## Incompatibilities with Older Configurations
+
+**WARNING**
+
+The current NuttX build system supports *only* the new compressed,
+defconfig configuration files generated using the kconfig-frontends tools
+as described in the preceding section.  Support for the older, legacy,
+manual configurations was eliminated in NuttX 7.0; support for
+uncompressed .config-files-as-defconfig files was eliminated after
+NuttX-7.21.  All configurations must now be done using the
+kconfig-frontends tool.  The older manual configurations and the new
+kconfig-frontends configurations are not compatible.  Old legacy
+configurations can *not* be used with the kconfig-frontends tool and,
+hence, cannot be used with releases of NuttX 7.0 and beyond:
+
+If you run 'make menuconfig' with a legacy configuration the resulting
+configuration will probably not be functional.
+
+  > Q: How can I tell if a configuration is a new kconfig-frontends
+  >   configuration or an older, manual configuration?
+  >
+  > A: Only old, manual configurations will have an appconfig file
+  > 
+  > Q: How can I convert a older, manual configuration into a new,
+  >    kconfig-frontends toolchain.
+  >
+  > A: Refer to <http://www.nuttx.org/doku.php?id=wiki:howtos:convertconfig>
+  
+**WARNING**
+
+As described above, whenever you use a configuration, you really should
+always refresh the configuration with the following command *before* you
+make NuttX:
+
+    make oldconfig
+
+OR
+
+    make olddefconfig
+
+This will make sure that the configuration is up-to-date in the event that
+it has lapsed behind the current NuttX development (see the paragraph
+"Refreshing Configurations" above).  But this only works with *new*
+configuration files created with the kconfig-frontends tools.
+
+Further, this step is *NOT* optional with the new, compressed defconfig
+files.  It is a necessary step that will also uncompress the defconfig
+file, regenerating the .config and making it usable for NuttX builds.
+
+Never do `make oldconfig` (OR `make menuconfig`) on a  configuration that
+has not been converted to use the kconfig-frontends tools!  This will
+damage your configuration (see
+<http://www.nuttx.org/doku.php?id=wiki:howtos:convertconfig>).
+
+## NuttX Configuration Tool under DOS
+
+  Recent versions of NuttX support building NuttX from a native Windows
+  console window (see *Native Windows Build* below).  But kconfig-frontends
+  is a Linux tool.  At one time this was a problem for Windows users, but
+  now there are two specially modified versions of the kconfig-frontends
+  tools that can be used.  One can be found here:
+  <http://uvc.de/posts/linux-kernel-configuration-tool-kconfig-under-windows.html>
+
+  The configuration steps of the most recent versions of NuttX require the
+  kconfig-tweak tool that is not not available in the the above.  However,
+  there has been an update to this Kconfig Windows tools that does include
+  kconfig-tweak:  http://reclonelabs.com/more-kconfig-awesomeness-for-windows/
+
+  Source code is available here: <https://github.com/reclone/kconfig-frontends-win32>
+  and <https://github.com/reclone/kconfig-frontends-win32/releases>
+
+  It is also possible to use the version of kconfig-frontends built
+  under Cygwin outside of the Cygwin "sandbox" in a native Windows
+  environment:
+
+  1. You can run the configuration tool using Cygwin.  However, the
+     Cygwin Makefile.win will complain so to do this will, you have
+     to manually edit the .config file:
+     
+     a. Delete the line: CONFIG_WINDOWS_NATIVE=y
+     
+     b. Change the apps/ directory path, CONFIG_APPS_DIR to use Unix
+      
+        style delimiters.  For example, change "..\apps" to "../apps"
+     
+     And of course, after you use the configuration tool you need to
+     restore CONFIG_WINDOWS_NATIVE=y and the correct CONFIG_APPS_DIR.

Review comment:
       ```suggestion
        restore `CONFIG_WINDOWS_NATIVE=y` and the correct `CONFIG_APPS_DIR`.
   ```

##########
File path: README.md
##########
@@ -0,0 +1,2513 @@
+# APACHE NUTTX (INCUBATING)
+
+* Introduction
+  - Incubation Status
+* Community
+  - Getting Help
+  - Mailing Lists
+  - Issue Tracker
+  - Source Code
+  - Website Source Code
+* Environments
+  - Installing Cygwin
+  - Ubuntu Bash under Windows 10
+  - Using macOS
+* Installation
+  - Download and Unpack
+  - Semi-Optional apps/ Package
+  - Installation Directories with Spaces in the Path
+  - Downloading from Repositories
+  - Related Repositories
+  - Notes about Header Files
+* Configuring NuttX
+  - Instantiating "Canned" Configurations
+  - Refreshing Configurations
+  - NuttX Configuration Tool
+  - Finding Selections in the Configuration Menus
+  - Reveal Hidden Configuration Options
+  - Make Sure that You are on the Right Platform
+  - Comparing Two Configurations
+  - Making defconfig Files
+  - Incompatibilities with Older Configurations
+  - NuttX Configuration Tool under DOS
+* Toolchains
+  - Cross-Development Toolchains
+  - NuttX Buildroot Toolchain
+* Shells
+* Building NuttX
+  - Building
+  - Re-building
+  - Build Targets and Options
+  - Native Windows Build
+  - Installing GNUWin32
+* Cygwin Build Problems
+  - Strange Path Problems
+  - Window Native Toolchain Issues
+* Documentation
+
+# INTRODUCTION
+
+Apache NuttX (Incubating) is a real-time operating system (RTOS) with an
+emphasis on standards compliance and small footprint.  Scalable from 8-bit
+to 32-bit microcontroller environments, the primary governing standards in
+NuttX are POSIX and ANSI standards. Additional standard APIs from Unix and
+other common RTOSs (such as VxWorks) are adopted for functionality not
+available under these standards, or for functionality that is not
+appropriate for deeply-embedded environments (such as fork()).
+
+Extensive documentation can be found on the project wiki:
+  <https://cwiki.apache.org/NUTTX/Nuttx>
+
+## Incubation Status
+
+Apache NuttX (Incubating) is an effort undergoing Incubation at The Apache
+Software Foundation (ASF), sponsored by the Incubator.  For more on our
+incubation effort, please see the file DISCLAIMER-WIP, in the same
+directory as this README.
+
+For brevity, the rest of this file will refer to it as Apache NuttX or
+simply NuttX.
+
+# COMMUNITY
+
+Every volunteer project obtains its strength from the people involved in
+it.  We invite you to participate as much or as little as you choose.
+
+We encourage you to:
+
+  - Use our project and provide feedback.
+  - Provide us with use-cases.
+  - Report bugs and submit patches.
+  - Contribute code or documentation.
+
+## Getting Help
+
+The best place to get help is the developer's mailing list.  Please see
+the following section:
+
+## Mailing Lists
+
+Get help using NuttX or contribute to the project on our mailing lists:
+
+  * <de...@nuttx.apache.org> is for people who want to contribute code to NuttX.
+    * To subscribe, send an email to <de...@nuttx.apache.org>.
+    * To unsubscribe, send an email to <de...@nuttx.apache.org>.
+    * View the archives at:
+      <https://www.mail-archive.com/dev@nuttx.apache.org/>
+
+  * <co...@nuttx.apache.org> is a read-only list that notifies subscribers
+  about commit messages and patches to NuttX.
+    * To subscribe, send an email to <co...@nuttx.apache.org>.
+    * To unsubscribe, send an email to <co...@nuttx.apache.org>.
+    * View the archives at:
+      <https://www.mail-archive.com/commits@nuttx.apache.org/>
+
+## Issue Tracker
+
+### Bug Reports:
+
+Found bug? Send an email to the dev list: <de...@nuttx.apache.org>
+
+Before submitting an issue, please:
+
+  - Verify that the bug does in fact exist. 
+  
+  - Search the mailing list archives to verify there is no existing issue
+    reporting the bug you've found.
+ 
+  - Consider tracking down the bug yourself in the NuttX source code and
+    submitting a patch along with your bug report.  This is a great time
+    saver for the NuttX developers and helps ensure the bug will be fixed
+    quickly.
+  
+### Feature Requests:
+  
+Enhancement requests for new features are also welcome. The more concrete
+and rational the request is, the greater the chance it will incorporated
+into future releases.
+
+## Source Code
+
+The project sources are in two Git repositories.  The core OS is in
+incubator-nuttx and the apps repository is in incubator-nuttx-apps.  These
+are housed in GitBox on ASF servers and also mirrored at GitHub.  These
+are kept in sync, so you can use whichever option you prefer.
+
+  - NuttX core OS repository:
+    
+    - Primary:
+      <https://gitbox.apache.org/repos/asf?p=incubator-nuttx.git>
+    
+    - GitHub Mirror:
+      <https://github.com/apache/incubator-nuttx>
+  
+  - Apps repository:
+    
+    - Primary:
+      <https://gitbox.apache.org/repos/asf?p=incubator-nuttx-apps.git>
+    
+    - GitHub Mirror:
+      <https://github.com/apache/incubator-nuttx-apps>
+
+## Website Source Code
+
+The project website sources are accessible via the website source code
+  repository which is also mirrored in GitHub:
+
+- Primary:
+  <https://gitbox.apache.org/repos/asf?p=incubator-nuttx-website.git>
+
+- GitHub Mirror:
+  <https://github.com/apache/incubator-nuttx-website>
+
+# ENVIRONMENTS
+
+  NuttX requires a POSIX development environment such as you would find under
+  Linux or macOS.  NuttX may also be installed and built on Windows system
+  if you also provide such a POSIX development environment.  Options for a
+  POSIX development environment under Windows include:
+
+  - An installation of Linux on a virtual machine (VM) in Windows.  I have
+    not been happy using a VM myself.  I have had stability problems with
+    open source VMs and commercial VMs cost more than I want to spend.
+    Sharing files with Linux running in a VM is awkward;  sharing devices
+    connected to the Windows box with Linux in a VM is, at the very least,
+    confusing;  Using Windows tools (such as Segger J-Link) with files
+    built under the Linux VM is not a possibility.
+
+  - The Cygwin environment.  Instructions for installation of Cygwin on a
+    Windows system are provided in the following paragraph, "Installing
+    Cygwin".  Cygwin is a mature, well-tested, and very convenient
+    environment.  It is especially convenient if you  need to
+    integrate with Windows tools and files.  Downsides are that the
+    installation time is very long and the compile times are slow.
+
+  - Ubuntu/Bash shell under Windows 10.  This is a new option under
+    Windows 10.  See the section "Ubuntu Bash under Windows 10" below.
+    This is an improvement over Cygwin if your concern is compile time;
+    its build performance is comparable to native Linux, certainly better
+    than the Cygwin build time.  It also installs in a tiny fraction of
+    the time as Cygwin, perhaps 20 minutes for the basic Ubuntu install
+    (vs. more than a day for the complete Cygwin install).
+  
+    There have been even more recent ports of Linux environment to
+    Windows.  I need to update this section to include some mention of
+    these alternatives.
+
+  - The MSYS environment.  MSYS derives from an older version of Cygwin
+    simplified and adapted to work more naturally in the Windows
+    environment.  See <http://www.mingw.org/wiki/MSYS> if you are
+    interested in using MSYS.  The advantages of the MSYS environment is
+    that it is better integrted with the native Windows environment and
+    lighter weight; it uses only a  minimal number of add-on POSIX-land
+    tools.
+  
+    The download link in that Wiki takes you to the SourceForge download
+    site.  The SourceForge MSYS project has been stagnant for some time.
+    The MSYS project has more recently moved to
+    <http://odsn.net/projects/sfnet_mingwbundle>.  Downloads of current .zip
+    files are available there but no instructions for the installation.
+
+  - MSYS2 appears to be a re-write of MSYS based on a newer version of
+    Cygwin.  Is it available at <https://www.msys2.org>.  A windows
+    installer is available at that site along with very good installation
+    instructions.  The download is relatively quick (at least compared to
+    Cygwin) and the 'pacman' package management tool supports supports
+    simple system updates.  For example, 'pacman -S git' will install the
+    GIT command line utilities.
+
+  - Other POSIX environments.  Check out:
+    
+    - UnxUtils: <https://sourceforge.net/projects/unxutils/>,
+      <https://en.wikipedia.org/wiki/UnxUtils>
+    - MobaXterm: <https://mobaxterm.mobatek.net/>
+    - Gow: <https://github.com/bmatzelle/gow/wiki>
+  
+    **Disclaimer**:  In principle, these should work.  However, I have never
+    used any of these environments and cannot guarantee that there is
+    not some less-than-obvious issues.
+  
+NuttX can also be installed and built on a native Windows system, but with
+some potential tool-related issues (see the discussion "Native Windows
+Build" under "Building NuttX" below).  GNUWin32 is used to provide
+compatible native windows tools.
+
+## Installing Cygwin
+
+Installing Cygwin on your Windows PC is simple, but time consuming.  See
+<http://www.cygwin.com/> for installation instructions. Basically you just
+need to download a tiny setup.exe program and it does the real, network
+installation for you.
+
+Some Cygwin installation tips:
+
+  1. Install at `C:\cygwin`
+  
+  2. Install **everything**:  "Only the minimal base packages from the
+     Cygwin distribution are installed by default. Clicking on categories
+     and packages in the setup.exe package installation screen will
+     provide you with the ability to control what is installed or updated.
+     Clicking on the "Default" field next to the "All" category will
+     provide you with the opportunity to install every Cygwin package.
+     Be advised that this will download and install hundreds of megabytes
+     to your computer."
+   
+If you use the "default" installation, you will be missing many
+of the Cygwin utilities that you will need to build NuttX.  The
+build will fail in numerous places because of missing packages.
+
+NOTE: The last time I installed **everything**, the download was
+about 5GiB.  The server I selected was also very slow so it took
+over a day to do the whole install!
+
+NOTE: You don't really have to install **everything** but I cannot
+answer the question "Then what should I install?"  I don't know
+the answer to that and so will continue to recommend installing
+**everything**.
+
+You should certainly be able to omit "Science", "Math", and
+"Publishing".  You can try omitting KDE, Gnome, GTK, and other
+graphics packages if you don't plan to use them.
+
+Perhaps a minimum set would be those packages listed below for the
+"Ubuntu Bash under Windows 10" installation?
+
+**UPDATE**:  Sergey Frolov had success with the following minimal
+Cygwin configuration:
+   
+   1. After starting the Cygwin installer, keep the recommended
+      packages that are pre-selected in the default configuration.
+   
+   2. Using the installation tools, add the following packages:
+      
+        make (GNU make)  bison        libgmp3-dev
+        gcc-core         byacc        libmpfr-dev
+        gcc-g++          gperf        libmpc-dev
+        flex             gdb          automake-1.15
+        libncurses-dev   libgmp-dev
+   
+After installing Cygwin, you will get lots of links for installed
+tools and shells.  I use the RXVT native shell.  It is fast and reliable
+and does not require you to run the Cygwin X server (which is neither
+fast nor reliable).  Unless otherwise noted, the rest of these
+instructions assume that you are at a bash command line prompt in
+either Linux or in Cygwin shell.
+
+## Using MSYS
+
+MSYS is an environment the derives from Cygwin.  Thus, most things said
+about Cygwin apply equally to MSYS.  This section will, then, focus on
+the differences when using MSYS, specifically MSYS2.
+
+Here is it assumed that you have already downloaded and installed MSYS2
+from https://www.msys2.org using the windows installer available at that
+location.  It is also assumed that you have brought in the necessary
+tools using the 'pacman' package management tool Tools needed including:
+
+  pacman -S git
+  pacman -S make
+  pacman -S gcc
+  pacman -S gdb
+
+And possibly others depending upon your usage.  Then you will need to
+build and install kconfig-frontends per the instructions of the top-level
+README.txt file in the tools repository.  This requires the following
+additional tools:
+
+    pacman -S bison
+    pacman -S gperf
+    pacman -S ncurses-devel
+    pacman -S automake-wrapper
+    pacman -S autoconf
+    pacman -S pkg-config
+
+Because of some versioning issues, I had to run 'aclocal' prior to
+running the kconfig-frontends configure script.  See "Configuring NuttX"
+below for further information.
+
+Unlike Cygwin, MSYS does not support symbolic links.  The 'ln -s' command
+will, in fact, copy a directory!  This means that you Make.defs file will
+have to include definitions like:
+
+    ifeq ($(CONFIG_WINDOWS_MSYS),y)
+      DIRLINK = $(TOPDIR)/tools/copydir.sh
+      DIRUNLINK = $(TOPDIR)/tools/unlink.sh
+    endif
+
+This will force the directory copies to work in a way that can be handled
+by the NuttX build system.  NOTE:  The default link.sh script has been
+updated so that is should now be MSYS2 compatible.  The above is preferred
+but no longer necessary in the Make.defs file.
+
+To build the simulator under MSYS, you also need:
+
+    pacman -S zlib-devel
+
+It appears that you cannot use directory names with spaces in them like
+"/c/Program\ Files \(86\)" in the MSYS path variable.  I worked around this
+by create Windows junctions like this:
+
+  1. Open the a windows command terminal,
+  
+  2. CD to `c:\msys64`, then
+  
+  3. `mklink /j programfiles "C:/Program\ Files"` and
+  
+  4. `mklink /j programfiles86 "C:/Program\ Files\ \(x86\)"`
+     
+     They then show up as `/programfiles` and `/programfiles86` with the MSYS2
+     sandbox.  Those paths can then be used with the PATH variable.  I had
+     to do something similar for the path to the GNU Tools "ARM Embedded
+     Toolchain" which also has spaces in the path name.
+
+## Ubuntu Bash under Windows 10
+
+A better version of a command-line only Ubuntu under Windows 10 (beta)
+has recently been made available from Microsoft.
+
+### Installation
+
+Installation instructions abound on the Internet complete with screen
+shots.  I will attempt to duplicate those instructions in full here.
+Here are the simplified installation steps:
+
+  - Open *Settings*.
+  
+  - Click on *Update & security*.
+  
+  - Click on *For Developers*.
+  
+  - Under *Use developer features*, select the *Developer mode* option to
+    setup the environment to install Bash.
+  
+  - A message box should pop up.  Click *Yes* to turn on developer mode.
+  
+  - After the necessary components install, you'll need to restart your
+    computer.
+    
+    Once your computer reboots:
+  
+  - Open *Control Panel*.
+  
+  - Click on *Programs*.
+  
+  - Click on *Turn Windows features on or off*.
+  
+  - A list of features will pop up, check the *Windows Subsystem for Linux
+    (beta)* option.
+  
+  - Click *OK*.
+  
+  - Once the components installed on your computer, click the *Restart
+    now* button to complete the task.
+    
+    After your computer restarts, you will notice that Bash will not appear in
+    the *Recently added* list of apps, this is because Bash isn't actually
+    installed yet. Now that you have setup the necessary components, use the
+    following steps to complete the installation of Bash:
+  
+  - Open *Start*, do a search for `bash.exe`, and press *Enter*.
+  
+  - On the command prompt, type `y` and press Enter to download and install
+    Bash from the Windows Store.  This will take awhile.
+  
+  - Then you'll need to create a default UNIX user account. This account
+    doesn't have to be the same as your Windows account. Enter the
+    username in the required field and press Enter (you can't use the
+    username `admin`).
+  
+  - Close the `bash.exe` command prompt.
+  
+  Now that you completed the installation and setup, you can open the Bash
+  tool from the Start menu like you would with any other app.
+
+### Accessing Windows Files from Ubuntu
+
+File systems will be mounted under `/mnt` so for example `C:\Program Files`
+appears at `/mnt/c/Program Files`.  This is as opposed to Cygwin where
+the same directory would appear at `/cygdrive/c/Program Files`.
+
+With these differences (perhaps a few other Windows quirks) the Ubuntu
+install works just like Ubuntu running natively on your PC.
+
+A good tip for file sharing is to use symbolic links within your Ubuntu
+home directory.  For example, suppose you have your `projects` directory
+at `C:\Documents\projects`.  Then you can set up a link to the `projects/`
+directory in your Ubuntu directory like:
+
+    ln -s /mnt/c/Documents/projects projects
+
+### Accessing Ubuntu Files From Windows
+
+In Ubuntu Userspace for Windows, the Ubuntu file system root directory is
+at:
+
+    %localappdata%\lxss\rootfs
+
+Or
+
+    C:\Users\Username\AppData\Local\lxss\rootfs
+
+However, I am unable to see my files under the rootfs\home directory.
+After some looking around, I find the home directory
+`%localappdata%\lxss\home`.
+
+With that trick access to the `/home` directory, you should actually be
+able to use Windows tools outside of the Ubuntu sandbox with versions of
+NuttX built within the sandbox using that path.
+
+### Executing Windows Tools from Ubuntu
+
+You can also execute Windows tools from within the Ubuntu sandbox:
+
+    /mnt/c/Program\ Files\ \(x86\)/Microchip/xc32/v1.43/bin/xc32-gcc.exe --version
+    Unable to translate current working directory. Using C:\WINDOWS\System32
+    xc32-gcc.exe (Microchip Technology) 4.8.3 MPLAB XC32 Compiler v1.43 Build date: Mar  1 2017
+    ...
+
+The error message indicates that there are more issues:  You cannot mix
+Windows tools that use Windows style paths in an environment that uses
+POSIX paths.  I think you would have to use Linux tools only from within
+the Ubuntu sandbox.
+
+### Install Ubuntu Software
+
+Use `sudo apt-get install <package name>`.  As examples, this is how
+you would get GIT:
+
+    sudo apt-get install git
+
+This will get you a compiler for your host PC:
+
+    sudo apt-get install gcc
+
+This will get you an ARM compiler for your target:
+
+    sudo apt-get install gcc-arm-none-eabi
+
+**NOTE**: That is just an example.  I am not sure if apt-get will give you a
+current or usable compiler.  You should carefully select your toolchain
+for the needs of your project.
+
+You will also need to get the kconfig-frontends configuration as
+described below under *NuttX Configuration Tool*.  In order to build the
+kconfig-frontends configuration tool you will also need: `make`, `gperf`,
+`flex`, `bison`, and `libncurses-dev`.
+
+That is enough to do a basic NuttX build.
+
+### Integrating with Windows Tools
+
+If you want to integrate with Windows native tools, then you would need
+deal with the same kind of craziness as with integrating Cygwin with
+native toolchains, see the section *Cygwin Build Problems* below.
+
+However, there is currently no build support for using Windows native
+tools with Ubuntu under Windows.  This tool combination is made to work
+with Cygwin through the use of the `cygpath -w` tool that converts paths
+from say `/cydrive/c/Program Files` to `C:\Program Files`.  There is,
+however, no corresponding tool to convert `/mnt/c/Program Files` in the
+Ubuntu environment.
+
+### Graphics Support
+
+The Ubuntu version support by Microsoft is a command-line only version.
+There is no support for Linux graphics utilities.
+
+This limitation is not a limitation of Ubuntu, however, only in what
+Microsoft is willing to support.  If you install a X-Server, then you
+can also use basic graphics utilities.  See for example:
+
+  <http://www.howtogeek.com/261575/how-to-run-graphical-linux-desktop-applications-from-windows-10s-bash-shell/>
+
+Many Linux graphics programs would, however, also require a graphics
+framework like GTK or Qt.  So this might be a trip down the rabbit hole.
+
+### Using macOS
+
+You need to install at least the following tools specific to macOS.
+
+  * flock (used by APPDIR build logic)
+    
+A macOS port is available at: <https://github.com/discoteq/flock>
+  
+    brew tap discoteq/discoteq
+    brew install flock
+  
+  If you want to build the sim:
+
+  * Xcode (the native compiler and the rest of the toolchain)
+
+  * ELF toolchain (if you want to build modules for CONFIG_LIBC_MODLIB)
+
+    brew install x86_64-elf-gc
+
+# INSTALLATION
+
+There are two ways to get NuttX:  You may download released, stable
+tarballs from either the project website.  Or you may get NuttX by
+cloning the GIT repositories.  Let's consider the released tarballs
+first:
+
+## Download and Unpack
+
+Download and unpack the NuttX tarball.  If you are reading this, then
+you have probably already done that.  After unpacking, you will end
+up with a directory called nuttx-version (where version is the NuttX
+version number). You might want to rename that directory nuttx to
+match the various instructions in the documentation and some scripts
+in the source tree.
+
+  * Download location:
+  
+    <https://nuttx.apache.org/download/>
+  
+  * Legacy download locations:
+
+    <https://bitbucket.org/nuttx/nuttx/downloads>  
+    <https://sourceforge.net/projects/nuttx/files/nuttx/>
+
+## Semi-Optional apps/ Package
+
+All NuttX libraries and example code used to be in included within
+the NuttX source tree.  As of NuttX-6.0, this application code was
+moved into a separate tarball, the apps tarball.  If you are just
+beginning with NuttX, then you will want to download the versioned
+apps tarball along with the NuttX tarball.  If you already have your
+own product application directory, then you may not need the apps
+tarball.
+
+It is called "Semi-optional" because if you don't have some `apps/`
+directory, NuttX will *fail* to build! You do not necessarily need
+to use the NuttX apps tarball but may, instead, provide your own
+custom application directory.  Such a custom directory would need
+to include a valid Makefile to support the build and a valid Kconfig
+file to support the configuration.  More about these files later.
+
+Download then unpack the apps tarball in the same directory where you
+unpacked the NuttX tarball.  After you unpack the apps tarball, you
+will have a new directory called apps-version (where the version
+should exactly match the version of the NuttX tarball).  Again, you
+might want to rename the directory to simply apps/ to match what
+you read in the documentation
+
+After unpacking (and renaming) the apps tarball, you will have two
+directories side by side like this:
+
+             |
+        +----+----+
+        |         |
+      nuttx/     apps/
+
+This is important because the NuttX build will expect to find the
+apps directory in that (default) location.  That default location
+can be changed by modifying your NuttX configuration file, but that
+is another story.
+
+## Installation Directories with Spaces in the Path
+
+The nuttx build directory should reside in a path that contains no
+spaces in any higher level directory name.  For example, under
+Cygwin, your home directory might be formed from your first and last
+names like: `/home/First Last`. That will cause strange errors when
+the make system tries to build.
+
+[Actually, that problem is probably not too difficult to fix.  Some
+ Makefiles probably just need some paths within double quotes]
+
+I work around spaces in the home directory name, by creating a
+new directory that does not contain any spaces, such as `/home/nuttx`.
+Then I install NuttX in `/home/nuttx` and always build from
+`/home/nuttx/nuttx-code`.
+
+## Downloading from Repositories
+
+### Cloning the Repository
+
+**BEFORE** cloning repositories on any Windows platform do the following GIT
+command:
+
+    git config --global core.autocrlf false
+
+That will avoid conversions of linefeeds (newlines, \n) to carriage
+return plus linefeed sequences (\r\n)
+
+The current NuttX du jour is available in from a GIT repository.  Here are
+instructions for cloning the core NuttX RTOS (corresponding to the nuttx
+tarball discussed above):
+
+    git clone https://gitbox.apache.org/repos/asf/incubator-nuttx.git nuttx
+
+-or-
+
+    git clone https://github.com/apache/incubator-nuttx.git nuttx
+
+And the semi-optional apps/ application directory and be cloned like:
+
+    git clone https://gitbox.apache.org/repos/asf/incubator-nuttx-apps.git apps
+  
+-or-
+  
+    git clone https://github.com/apache/incubator-nuttx-apps.git apps
+
+That will give you the same directory structure like this:
+    
+             |
+        +----+----+
+        |         |
+      nuttx/     apps/
+
+### Configuring the Clones
+
+The following steps need to be performed for each of the repositories.
+After changing to the clone directory:
+
+Set your identity:
+
+    git config --global user.name "My Name"
+    git config --global user.email my.name@example.com
+  
+Colorized diffs are much easier to read:
+
+    git config --global color.branch auto
+    git config --global color.diff auto
+    git config --global color.interactive auto
+    git config --global color.status auto
+
+Checkout other settings
+
+    git config --list
+
+### Cloning NuttX Inside Cygwin
+
+If you are cloning the NuttX repository, it is recommended to avoid
+automatic end of lines conversions by git. These conversions may break
+some scripts like configure.sh. Before cloning, do the following:
+
+    git config --global core.autocrlf false
+
+## Related Repositories
+
+These are standalone repositories:
+
+  * <https://gitbox.apache.org/repos/asf/incubator-nuttx-apps>  
+    or  
+    <https://github.com/apache/incubator-nuttx-apps.git>
+    
+    This directory holds an optional package of applications and libraries
+    can be used with the NuttX RTOS.  There is a README.txt file there that
+    will provide more information about that package.
+
+  * <https://bitbucket.org/nuttx/nxwidgets>
+  
+    This is the NuttX C++ graphics support.  This includes NxWM, the tiny
+    NuttX Window Manager.
+
+  * <https://bitbucket.org/nuttx/uclibc>
+  
+    This repository contains a version of the uClibc++ C++ library.  This code
+    originates from <http://cxx.uclibc.org/> and has been adapted for NuttX by the
+    RGMP team (<http://rgmp.sourceforge.net/wiki/index.php/Main_Page>).
+
+  * <https://bitbucket.org/nuttx/buildroot>
+  
+    A environment that you can to use to build a custom, NuttX GNU toolchain.
+
+  * <https://bitbucket.org/nuttx/tools>
+  
+    There are snapshots of some tools here that you will need to work with
+    NuttX:  kconfig-frontends, genromfs, and others.
+
+## Notes about Header Files
+
+### Other C-Library Header Files
+
+When a GCC toolchain is built, it must be built against a C library.
+The compiler together with the contents of the C library completes the
+C language definition and provides the complete C development
+environment.  NuttX provides its own, built-in C library.  So the
+complete, consistent C language definition for use with NuttX comes from
+the combination of the compiler and the header files provided by the
+NuttX C library.
+
+When a GCC toolchain is built, it incorporates the C library header
+files into the compiler internal directories and, in this way, the C
+library really becomes a part of the toolchain.  If you use the NuttX
+buildroot toolchain as described below under "NuttX Buildroot
+Toolchain", your GCC toolchain will build against the NuttX C library
+and will incorporate the NuttX C library header files as part of the
+toolchain.
+
+If you use some other, third-party tool chain, this will not be the
+case, however.  Those toolchains were probably built against some
+other, incompatible C library distribution (such as newlib).  Those
+tools will have incorporated the incompatible C library header files
+as part of the toolchain.  These incompatible header files must *not*
+be used with NuttX because they will conflict with definitions in the
+NuttX built-in C-Library.  For such toolchains that include header
+files from a foreign C-Library, NuttX must be compiled without using
+the standard header files that are distributed with your toolchain.
+This prevents including conflicting, incompatible header files such
+as stdio.h.
+
+The math.h and stdarg.h are probably the two most trouble some header
+files to deal with.  These troublesome header files are discussed in
+more detail below.
+
+### Header Files Provided by Your Toolchain
+
+Certain header files, such as `setjmp.h`, `stdarg.h`, and `math.h`, may still
+be needed from your toolchain and your compiler may not, however, be able
+to find these if you compile NuttX without using standard header files
+(i.e., with `-nostdinc`).  If that is the case, one solution is to copy
+those header file from your toolchain into the NuttX include directory.
+
+### Duplicated Header Files
+
+There are also a few header files that can be found in the `nuttx/include`
+directory which are duplicated by the header files from your toolchain.
+stdint.h and stdbool.h are examples.  If you prefer to use the `stdint.h`
+and `stdbool.h` header files from your toolchain, those could be copied
+into the `nuttx/include/` directory. Using most other header files from
+your toolchain would probably cause errors.
+
+### math.h
+
+Even though you should not use a foreign C-Library, you may still need
+to use other, external libraries with NuttX.  In particular, you may
+need to use the math library, libm.a.  NuttX supports a generic, built-in
+math library that can be enabled using `CONFIG_LIBM=y`.  However, you may
+still want to use a higher performance external math library that has
+been tuned for your CPU.  Sometimes such tuned math libraries are
+bundled with your toolchain.
+
+The math library header file, `math.h`, is a then special case.  If you do
+nothing, the standard math.h header file that is provided with your
+toolchain will be used.
+
+If you have a custom, architecture specific math.h header file, then
+that header file should be placed at `arch/<cpu>/include/math.h`.  There
+is a stub `math.h` header file located at `include/nuttx/lib/math.h`.  This stub
+header file can be used to "redirect" the inclusion to an architecture-
+specific math.h header file.  If you add an architecture specific math.h
+header file then you should also define `CONFIG_ARCH_MATH_H=y` in your
+NuttX Configuration file.  If `CONFIG_ARCH_MATH_H` is selected, then the
+top-level Makefile will copy the stub math.h header file from
+`include/nuttx/lib/math.h` to `include/math.h` where it will become the system
+`math.h` header file.  The stub `math.h` header file does nothing other
+than to include that architecture-specific `math.h` header file as the
+system `math.h` header file.
+
+### float.h
+
+If you enable the generic, built-in math library, then that math library
+will expect your toolchain to provide the standard `float.h` header file.
+The float.h header file defines the properties of your floating point
+implementation.  It would always be best to use your toolchain's `float.h`
+header file but if none is available, a default `float.h` header file will
+be provided if this option is selected.  However, there is no assurance
+that the settings in this `float.h` are actually correct for your platform!
+
+### stdarg.h
+
+In most cases, the correct version of stdarg.h is the version provided
+with your toolchain.  However, sometimes there are issues with
+using your toolchains `stdarg.h`.  For example, it may attempt to draw in
+header files that do not exist in NuttX or perhaps the header files that
+it uses are not compatible with the NuttX header files.  In those cases,
+you can use an architecture-specific `stdarg.h` header file by defining
+`CONFIG_ARCH_STDARG_H=y`.
+
+See the discussion above for the `math.h` header.  This setting works
+exactly the same for the `stdarg.h` header file.
+
+# CONFIGURING NUTTX
+
+## Instantiating "Canned" Configurations
+
+### `configure.sh` and `configure.bat`
+
+"Canned" NuttX configuration files are retained in:
+
+    boards/<arch-name>/<chip-name>/<board-name>/configs/<config-dir>
+
+Where `<board-name>` is the name of your development board and `<config-dir>`
+is the name of the sub-directory containing a specific configuration for
+that board. `<arch-name>` and `<chip-name>` refer to characteristics of the
+MCU used on the board: `<arch-name>` is the CPU architecture implemented
+by the MCU; `<chip-name>` identifies the MCU chip family.  Only a few
+steps are required to instantiate a NuttX configuration, but to make the
+configuration even easier there are scripts available in the tools/
+sub-directory combines those simple steps into one command.
+
+There is one tool for use with any Bash-like shell that does configuration
+steps.  It is used as follows:
+
+    tools/configure.sh <board-name>:<config-dir>
+
+There is an alternative Windows batch file that can be used in the windows
+native environment like:
+
+    tools\configure.bat <board-name>:<config-dir>
+
+And, to make sure that other platforms are supported, there is also a
+C program at tools/configure.c that can be compiled to establish the
+board configuration.
+
+See `tools/README.txt` for more information about these scripts.
+
+General information about configuring NuttX can be found in:
+
+    {TOPDIR}/boards/README.txt
+    {TOPDIR}/boards/<arch-name>/<chip-name>/<board-name>/README.txt
+
+### The Hidden Configuration Scripts:
+
+As mentioned above, there are only a few simple steps to instantiating a
+NuttX configuration.  Those steps are hidden by the configuration scripts
+but are summarized below:
+  
+  1. Copy Files
+  
+     Configuring NuttX requires only copying two files from the
+     `<config-dir>` to the directory where you installed NuttX (TOPDIR):
+  
+       * Copy `boards/<arch-name>/<chip-name>/<board-name>/configs/<config-dir>/Make.def` to `{TOPDIR}/Make.defs`
+    
+         OR
+    
+       * Copy `boards/<arch-name>/<chip-name>/<board-name>/scripts/Make.def`
+         to `{TOPDIR}/Make.defs`
+    
+         Make.defs describes the rules needed by your tool chain to compile
+         and link code.  You may need to modify this file to match the
+         specific needs of your toolchain.  NOTE that a configuration may
+         have its own unique Make.defs file in its configuration directory or
+         it may use a common Make.defs file for the board in the scripts/
+         directory.  The first takes precedence.
+    
+       * Copy `boards/<arch-name>/<chip-name>/<board-name>/configs/<config-dir>/defconfig` to `{TOPDIR}/.config`
+    
+         The defconfig file holds the actual build configuration.  This
+         file is included by all other make files to determine what is
+         included in the build and what is not.  This file is also used
+         to generate a C configuration header at `include/nuttx/config.h`.
+    
+       * Copy other, environment-specific files to `{TOPDIR}`
+    
+         This might include files like .gdbinit or IDE configuration files
+         like .project or .cproject.
+  
+  2. Refresh the Configuration
+  
+     New configuration setting may be added or removed.  Existing settings
+     may also change there values or options.  This must be handled by
+     refreshing the configuration as described below.
+    
+     NOTE:  NuttX uses only compressed defconfig files.  For the NuttX
+     defconfig files, this refreshing step is *NOT* optional; it is also
+     necessary to uncompress and regenerate the full making file.  This is
+     discussed further below.
+
+## Refreshing Configurations
+
+Configurations can get out of date.  As new configuration settings are
+added or removed or as dependencies between configuration settings
+change, the contents of a default configuration can become out of synch
+with the build systems.  Hence, it is a good practice to "refresh" each
+configuration after configuring and before making.  To refresh the
+configuration, use the NuttX Configuration Tool like this:
+
+    make oldconfig
+
+AFTER you have instantiated the NuttX configuration as described above.
+The configuration step copied the .config file into place in the top-level
+NuttX directory; 'make oldconfig' step will then operate on that .config
+file to bring it up-to-date.
+
+If your configuration is out of date, you will be prompted by 'make oldconfig'
+to resolve the issues detected by the configuration tool, that is, to
+provide values for the new configuration options in the build system.  Doing
+this can save you a lot of problems down the road due to obsolete settings in
+the default board configuration file.  The NuttX configuration tool is
+discussed in more detail in the following paragraph.
+
+Confused about what the correct value for a new configuration item should
+be?  Enter ? in response to the 'make oldconfig' prompt and it will show
+you the help text that goes with the option.
+
+If you don't want to make any decisions are willing to just accept the
+recommended default value for each new configuration item, an even easier
+way is:
+
+    make olddefconfig
+
+The olddefconfig target will simply bring your configuration up to date with
+the current Kconfig files, setting any new options to the default value.
+No questions asked.
+
+## NuttX Configuration Tool
+
+An automated tool has been incorporated to support re-configuration
+of NuttX.  This tool is based on the kconfig-frontends application available
+at <https://bitbucket.org/nuttx/tools/src/master/kconfig-frontends/>.  (This
+is a snapshot of the old <http://ymorin.is-a-geek.org/projects/kconfig-frontends>
+which is no longer available.)  This application provides a tool called
+`kconfig-mconf` that is used by the NuttX top-level Makefile. The following
+make target is provided:
+
+    make menuconfig
+
+This make target will bring up NuttX configuration menus.
+
+**WARNING**:  Never do `make menuconfig` on a configuration that has
+not been converted to use the kconfig-frontends tools!  This will
+damage your configuration (see
+<http://www.nuttx.org/doku.php?id=wiki:howtos:convertconfig>).
+
+How do we tell a new configuration from an old one? See "Incompatibilities
+with Older Configurations" below.
+
+The `menuconfig` make target depends on two things:
+
+  1. The Kconfig configuration data files that appear in almost all
+     NuttX directories.  These data files are the part that is still
+     under development (patches are welcome!).  The Kconfig files
+     contain configuration information for the configuration settings
+     relevant to the directory in which the Kconfig file resides.
+     
+     NOTE: For a description of the syntax of this configuration file,
+     see kconfig-language.txt in the tools repository at
+     <https://bitbucket.org/nuttx/tools>
+  
+  2. The `kconfig-mconf` tool. `kconfig-mconf` is part of the
+     kconfig-frontends package.  You can download that package from the
+     snapshot in the tools repository at <https://bitbucket.org/nuttx/tools>.
+  
+     Building kconfig-frontends under Linux may be as simple as
+     `configure; make; make install` but there may be some build
+     complexities, especially if you are building under Cygwin.  See
+     the more detailed build instructions in the top-level README.txt
+     file of the tools repository at <https://bitbucket.org/nuttx/tools>.
+  
+  
+     The `make install` step will, by default, install the `kconfig-mconf`
+     tool at `/usr/local/bin/mconf`.  Where ever you choose to
+     install `kconfig-mconf`, make certain that your PATH variable includes
+     a path to that installation directory.
+  
+     The kconfig-frontends tools will not build in a native Windows
+     environment directly "out-of-the-box".  For the Windows native
+     case, you can use the modified version of kconfig-frontends
+     that can be found at
+
+     <http://uvc.de/posts/linux-kernel-configuration-tool-kconfig-under-windows.html>  
+
+     or a more recent port that can be found at  
+
+     <http://reclonelabs.com/more-kconfig-awesomeness-for-windows/>.
+   
+The basic configuration order is "bottom-up":
+   
+   - Select the build environment,
+   - Select the processor,
+   - Select the board,
+   - Select the supported peripherals
+   - Configure the device drivers,
+   - Configure the application options on top of this.
+   
+This is pretty straight forward for creating new configurations
+but may be less intuitive for modifying existing configurations.
+
+Another ncurses-based tool that is an option to kconfig-mconf is
+kconfig-nconf.  The differences are primary in in the aesthetics of the
+UI.  If you have kconfig-nconf built, then you can invoke that front end
+with:
+   
+     make nconfig
+   
+If you have an environment that supports the Qt or GTK graphical systems
+(probably KDE or gnome, respectively, or Cygwin under Windows with Qt or
+GTK installed), then you can also build the graphical kconfig-frontends,
+kconfig-qconf and kconfig-gconf.  In these case, you can start the
+graphical configurator with either:
+   
+     make qconfig
+   
+ or
+   
+     make gconfig
+   
+Some keyboard shortcuts supported by kconfig-mconf, the tool that runs
+when you do 'make menuconfig':
+
+   - `?` will bring up the mconfig help display.
+   
+   - `/` can be used find configuration selections.
+   
+   - `Z` can be used to reveal hidden configuration options
+   
+These last two shortcuts are described further in the following
+paragraphs.
+
+## Finding Selections in the Configuration Menus
+
+The NuttX configuration options have gotten complex and it can be very
+difficult to find options in the menu trees if you are not sure where
+to look.  The "basic configuration order" describe above can help to
+narrow things down.
+
+But if you know exactly what configuration setting you want to select,
+say CONFIG_XYZ, but not where to find it, then the 'make menuconfig'

Review comment:
       ```suggestion
   say `CONFIG_XYZ`, but not where to find it, then the `make menuconfig`
   ```

##########
File path: README.md
##########
@@ -0,0 +1,2513 @@
+# APACHE NUTTX (INCUBATING)
+
+* Introduction
+  - Incubation Status
+* Community
+  - Getting Help
+  - Mailing Lists
+  - Issue Tracker
+  - Source Code
+  - Website Source Code
+* Environments
+  - Installing Cygwin
+  - Ubuntu Bash under Windows 10
+  - Using macOS
+* Installation
+  - Download and Unpack
+  - Semi-Optional apps/ Package
+  - Installation Directories with Spaces in the Path
+  - Downloading from Repositories
+  - Related Repositories
+  - Notes about Header Files
+* Configuring NuttX
+  - Instantiating "Canned" Configurations
+  - Refreshing Configurations
+  - NuttX Configuration Tool
+  - Finding Selections in the Configuration Menus
+  - Reveal Hidden Configuration Options
+  - Make Sure that You are on the Right Platform
+  - Comparing Two Configurations
+  - Making defconfig Files
+  - Incompatibilities with Older Configurations
+  - NuttX Configuration Tool under DOS
+* Toolchains
+  - Cross-Development Toolchains
+  - NuttX Buildroot Toolchain
+* Shells
+* Building NuttX
+  - Building
+  - Re-building
+  - Build Targets and Options
+  - Native Windows Build
+  - Installing GNUWin32
+* Cygwin Build Problems
+  - Strange Path Problems
+  - Window Native Toolchain Issues
+* Documentation
+
+# INTRODUCTION
+
+Apache NuttX (Incubating) is a real-time operating system (RTOS) with an
+emphasis on standards compliance and small footprint.  Scalable from 8-bit
+to 32-bit microcontroller environments, the primary governing standards in
+NuttX are POSIX and ANSI standards. Additional standard APIs from Unix and
+other common RTOSs (such as VxWorks) are adopted for functionality not
+available under these standards, or for functionality that is not
+appropriate for deeply-embedded environments (such as fork()).
+
+Extensive documentation can be found on the project wiki:
+  <https://cwiki.apache.org/NUTTX/Nuttx>
+
+## Incubation Status
+
+Apache NuttX (Incubating) is an effort undergoing Incubation at The Apache
+Software Foundation (ASF), sponsored by the Incubator.  For more on our
+incubation effort, please see the file DISCLAIMER-WIP, in the same
+directory as this README.
+
+For brevity, the rest of this file will refer to it as Apache NuttX or
+simply NuttX.
+
+# COMMUNITY
+
+Every volunteer project obtains its strength from the people involved in
+it.  We invite you to participate as much or as little as you choose.
+
+We encourage you to:
+
+  - Use our project and provide feedback.
+  - Provide us with use-cases.
+  - Report bugs and submit patches.
+  - Contribute code or documentation.
+
+## Getting Help
+
+The best place to get help is the developer's mailing list.  Please see
+the following section:
+
+## Mailing Lists
+
+Get help using NuttX or contribute to the project on our mailing lists:
+
+  * <de...@nuttx.apache.org> is for people who want to contribute code to NuttX.
+    * To subscribe, send an email to <de...@nuttx.apache.org>.
+    * To unsubscribe, send an email to <de...@nuttx.apache.org>.
+    * View the archives at:
+      <https://www.mail-archive.com/dev@nuttx.apache.org/>
+
+  * <co...@nuttx.apache.org> is a read-only list that notifies subscribers
+  about commit messages and patches to NuttX.
+    * To subscribe, send an email to <co...@nuttx.apache.org>.
+    * To unsubscribe, send an email to <co...@nuttx.apache.org>.
+    * View the archives at:
+      <https://www.mail-archive.com/commits@nuttx.apache.org/>
+
+## Issue Tracker
+
+### Bug Reports:
+
+Found bug? Send an email to the dev list: <de...@nuttx.apache.org>
+
+Before submitting an issue, please:
+
+  - Verify that the bug does in fact exist. 
+  
+  - Search the mailing list archives to verify there is no existing issue
+    reporting the bug you've found.
+ 
+  - Consider tracking down the bug yourself in the NuttX source code and
+    submitting a patch along with your bug report.  This is a great time
+    saver for the NuttX developers and helps ensure the bug will be fixed
+    quickly.
+  
+### Feature Requests:
+  
+Enhancement requests for new features are also welcome. The more concrete
+and rational the request is, the greater the chance it will incorporated
+into future releases.
+
+## Source Code
+
+The project sources are in two Git repositories.  The core OS is in
+incubator-nuttx and the apps repository is in incubator-nuttx-apps.  These
+are housed in GitBox on ASF servers and also mirrored at GitHub.  These
+are kept in sync, so you can use whichever option you prefer.
+
+  - NuttX core OS repository:
+    
+    - Primary:
+      <https://gitbox.apache.org/repos/asf?p=incubator-nuttx.git>
+    
+    - GitHub Mirror:
+      <https://github.com/apache/incubator-nuttx>
+  
+  - Apps repository:
+    
+    - Primary:
+      <https://gitbox.apache.org/repos/asf?p=incubator-nuttx-apps.git>
+    
+    - GitHub Mirror:
+      <https://github.com/apache/incubator-nuttx-apps>
+
+## Website Source Code
+
+The project website sources are accessible via the website source code
+  repository which is also mirrored in GitHub:
+
+- Primary:
+  <https://gitbox.apache.org/repos/asf?p=incubator-nuttx-website.git>
+
+- GitHub Mirror:
+  <https://github.com/apache/incubator-nuttx-website>
+
+# ENVIRONMENTS
+
+  NuttX requires a POSIX development environment such as you would find under
+  Linux or macOS.  NuttX may also be installed and built on Windows system
+  if you also provide such a POSIX development environment.  Options for a
+  POSIX development environment under Windows include:
+
+  - An installation of Linux on a virtual machine (VM) in Windows.  I have
+    not been happy using a VM myself.  I have had stability problems with
+    open source VMs and commercial VMs cost more than I want to spend.
+    Sharing files with Linux running in a VM is awkward;  sharing devices
+    connected to the Windows box with Linux in a VM is, at the very least,
+    confusing;  Using Windows tools (such as Segger J-Link) with files
+    built under the Linux VM is not a possibility.
+
+  - The Cygwin environment.  Instructions for installation of Cygwin on a
+    Windows system are provided in the following paragraph, "Installing
+    Cygwin".  Cygwin is a mature, well-tested, and very convenient
+    environment.  It is especially convenient if you  need to
+    integrate with Windows tools and files.  Downsides are that the
+    installation time is very long and the compile times are slow.
+
+  - Ubuntu/Bash shell under Windows 10.  This is a new option under
+    Windows 10.  See the section "Ubuntu Bash under Windows 10" below.
+    This is an improvement over Cygwin if your concern is compile time;
+    its build performance is comparable to native Linux, certainly better
+    than the Cygwin build time.  It also installs in a tiny fraction of
+    the time as Cygwin, perhaps 20 minutes for the basic Ubuntu install
+    (vs. more than a day for the complete Cygwin install).
+  
+    There have been even more recent ports of Linux environment to
+    Windows.  I need to update this section to include some mention of
+    these alternatives.
+
+  - The MSYS environment.  MSYS derives from an older version of Cygwin
+    simplified and adapted to work more naturally in the Windows
+    environment.  See <http://www.mingw.org/wiki/MSYS> if you are
+    interested in using MSYS.  The advantages of the MSYS environment is
+    that it is better integrted with the native Windows environment and
+    lighter weight; it uses only a  minimal number of add-on POSIX-land
+    tools.
+  
+    The download link in that Wiki takes you to the SourceForge download
+    site.  The SourceForge MSYS project has been stagnant for some time.
+    The MSYS project has more recently moved to
+    <http://odsn.net/projects/sfnet_mingwbundle>.  Downloads of current .zip
+    files are available there but no instructions for the installation.
+
+  - MSYS2 appears to be a re-write of MSYS based on a newer version of
+    Cygwin.  Is it available at <https://www.msys2.org>.  A windows
+    installer is available at that site along with very good installation
+    instructions.  The download is relatively quick (at least compared to
+    Cygwin) and the 'pacman' package management tool supports supports
+    simple system updates.  For example, 'pacman -S git' will install the
+    GIT command line utilities.
+
+  - Other POSIX environments.  Check out:
+    
+    - UnxUtils: <https://sourceforge.net/projects/unxutils/>,
+      <https://en.wikipedia.org/wiki/UnxUtils>
+    - MobaXterm: <https://mobaxterm.mobatek.net/>
+    - Gow: <https://github.com/bmatzelle/gow/wiki>
+  
+    **Disclaimer**:  In principle, these should work.  However, I have never
+    used any of these environments and cannot guarantee that there is
+    not some less-than-obvious issues.
+  
+NuttX can also be installed and built on a native Windows system, but with
+some potential tool-related issues (see the discussion "Native Windows
+Build" under "Building NuttX" below).  GNUWin32 is used to provide
+compatible native windows tools.
+
+## Installing Cygwin
+
+Installing Cygwin on your Windows PC is simple, but time consuming.  See
+<http://www.cygwin.com/> for installation instructions. Basically you just
+need to download a tiny setup.exe program and it does the real, network
+installation for you.
+
+Some Cygwin installation tips:
+
+  1. Install at `C:\cygwin`
+  
+  2. Install **everything**:  "Only the minimal base packages from the
+     Cygwin distribution are installed by default. Clicking on categories
+     and packages in the setup.exe package installation screen will
+     provide you with the ability to control what is installed or updated.
+     Clicking on the "Default" field next to the "All" category will
+     provide you with the opportunity to install every Cygwin package.
+     Be advised that this will download and install hundreds of megabytes
+     to your computer."
+   
+If you use the "default" installation, you will be missing many
+of the Cygwin utilities that you will need to build NuttX.  The
+build will fail in numerous places because of missing packages.
+
+NOTE: The last time I installed **everything**, the download was
+about 5GiB.  The server I selected was also very slow so it took
+over a day to do the whole install!
+
+NOTE: You don't really have to install **everything** but I cannot
+answer the question "Then what should I install?"  I don't know
+the answer to that and so will continue to recommend installing
+**everything**.
+
+You should certainly be able to omit "Science", "Math", and
+"Publishing".  You can try omitting KDE, Gnome, GTK, and other
+graphics packages if you don't plan to use them.
+
+Perhaps a minimum set would be those packages listed below for the
+"Ubuntu Bash under Windows 10" installation?
+
+**UPDATE**:  Sergey Frolov had success with the following minimal
+Cygwin configuration:
+   
+   1. After starting the Cygwin installer, keep the recommended
+      packages that are pre-selected in the default configuration.
+   
+   2. Using the installation tools, add the following packages:
+      
+        make (GNU make)  bison        libgmp3-dev
+        gcc-core         byacc        libmpfr-dev
+        gcc-g++          gperf        libmpc-dev
+        flex             gdb          automake-1.15
+        libncurses-dev   libgmp-dev
+   
+After installing Cygwin, you will get lots of links for installed
+tools and shells.  I use the RXVT native shell.  It is fast and reliable
+and does not require you to run the Cygwin X server (which is neither
+fast nor reliable).  Unless otherwise noted, the rest of these
+instructions assume that you are at a bash command line prompt in
+either Linux or in Cygwin shell.
+
+## Using MSYS
+
+MSYS is an environment the derives from Cygwin.  Thus, most things said
+about Cygwin apply equally to MSYS.  This section will, then, focus on
+the differences when using MSYS, specifically MSYS2.
+
+Here is it assumed that you have already downloaded and installed MSYS2
+from https://www.msys2.org using the windows installer available at that
+location.  It is also assumed that you have brought in the necessary
+tools using the 'pacman' package management tool Tools needed including:
+
+  pacman -S git
+  pacman -S make
+  pacman -S gcc
+  pacman -S gdb
+
+And possibly others depending upon your usage.  Then you will need to
+build and install kconfig-frontends per the instructions of the top-level
+README.txt file in the tools repository.  This requires the following
+additional tools:
+
+    pacman -S bison
+    pacman -S gperf
+    pacman -S ncurses-devel
+    pacman -S automake-wrapper
+    pacman -S autoconf
+    pacman -S pkg-config
+
+Because of some versioning issues, I had to run 'aclocal' prior to
+running the kconfig-frontends configure script.  See "Configuring NuttX"
+below for further information.
+
+Unlike Cygwin, MSYS does not support symbolic links.  The 'ln -s' command
+will, in fact, copy a directory!  This means that you Make.defs file will
+have to include definitions like:
+
+    ifeq ($(CONFIG_WINDOWS_MSYS),y)
+      DIRLINK = $(TOPDIR)/tools/copydir.sh
+      DIRUNLINK = $(TOPDIR)/tools/unlink.sh
+    endif
+
+This will force the directory copies to work in a way that can be handled
+by the NuttX build system.  NOTE:  The default link.sh script has been
+updated so that is should now be MSYS2 compatible.  The above is preferred
+but no longer necessary in the Make.defs file.
+
+To build the simulator under MSYS, you also need:
+
+    pacman -S zlib-devel
+
+It appears that you cannot use directory names with spaces in them like
+"/c/Program\ Files \(86\)" in the MSYS path variable.  I worked around this
+by create Windows junctions like this:
+
+  1. Open the a windows command terminal,
+  
+  2. CD to `c:\msys64`, then
+  
+  3. `mklink /j programfiles "C:/Program\ Files"` and
+  
+  4. `mklink /j programfiles86 "C:/Program\ Files\ \(x86\)"`
+     
+     They then show up as `/programfiles` and `/programfiles86` with the MSYS2
+     sandbox.  Those paths can then be used with the PATH variable.  I had
+     to do something similar for the path to the GNU Tools "ARM Embedded
+     Toolchain" which also has spaces in the path name.
+
+## Ubuntu Bash under Windows 10
+
+A better version of a command-line only Ubuntu under Windows 10 (beta)
+has recently been made available from Microsoft.
+
+### Installation
+
+Installation instructions abound on the Internet complete with screen
+shots.  I will attempt to duplicate those instructions in full here.
+Here are the simplified installation steps:
+
+  - Open *Settings*.
+  
+  - Click on *Update & security*.
+  
+  - Click on *For Developers*.
+  
+  - Under *Use developer features*, select the *Developer mode* option to
+    setup the environment to install Bash.
+  
+  - A message box should pop up.  Click *Yes* to turn on developer mode.
+  
+  - After the necessary components install, you'll need to restart your
+    computer.
+    
+    Once your computer reboots:
+  
+  - Open *Control Panel*.
+  
+  - Click on *Programs*.
+  
+  - Click on *Turn Windows features on or off*.
+  
+  - A list of features will pop up, check the *Windows Subsystem for Linux
+    (beta)* option.
+  
+  - Click *OK*.
+  
+  - Once the components installed on your computer, click the *Restart
+    now* button to complete the task.
+    
+    After your computer restarts, you will notice that Bash will not appear in
+    the *Recently added* list of apps, this is because Bash isn't actually
+    installed yet. Now that you have setup the necessary components, use the
+    following steps to complete the installation of Bash:
+  
+  - Open *Start*, do a search for `bash.exe`, and press *Enter*.
+  
+  - On the command prompt, type `y` and press Enter to download and install
+    Bash from the Windows Store.  This will take awhile.
+  
+  - Then you'll need to create a default UNIX user account. This account
+    doesn't have to be the same as your Windows account. Enter the
+    username in the required field and press Enter (you can't use the
+    username `admin`).
+  
+  - Close the `bash.exe` command prompt.
+  
+  Now that you completed the installation and setup, you can open the Bash
+  tool from the Start menu like you would with any other app.
+
+### Accessing Windows Files from Ubuntu
+
+File systems will be mounted under `/mnt` so for example `C:\Program Files`
+appears at `/mnt/c/Program Files`.  This is as opposed to Cygwin where
+the same directory would appear at `/cygdrive/c/Program Files`.
+
+With these differences (perhaps a few other Windows quirks) the Ubuntu
+install works just like Ubuntu running natively on your PC.
+
+A good tip for file sharing is to use symbolic links within your Ubuntu
+home directory.  For example, suppose you have your `projects` directory
+at `C:\Documents\projects`.  Then you can set up a link to the `projects/`
+directory in your Ubuntu directory like:
+
+    ln -s /mnt/c/Documents/projects projects
+
+### Accessing Ubuntu Files From Windows
+
+In Ubuntu Userspace for Windows, the Ubuntu file system root directory is
+at:
+
+    %localappdata%\lxss\rootfs
+
+Or
+
+    C:\Users\Username\AppData\Local\lxss\rootfs
+
+However, I am unable to see my files under the rootfs\home directory.
+After some looking around, I find the home directory
+`%localappdata%\lxss\home`.
+
+With that trick access to the `/home` directory, you should actually be
+able to use Windows tools outside of the Ubuntu sandbox with versions of
+NuttX built within the sandbox using that path.
+
+### Executing Windows Tools from Ubuntu
+
+You can also execute Windows tools from within the Ubuntu sandbox:
+
+    /mnt/c/Program\ Files\ \(x86\)/Microchip/xc32/v1.43/bin/xc32-gcc.exe --version
+    Unable to translate current working directory. Using C:\WINDOWS\System32
+    xc32-gcc.exe (Microchip Technology) 4.8.3 MPLAB XC32 Compiler v1.43 Build date: Mar  1 2017
+    ...
+
+The error message indicates that there are more issues:  You cannot mix
+Windows tools that use Windows style paths in an environment that uses
+POSIX paths.  I think you would have to use Linux tools only from within
+the Ubuntu sandbox.
+
+### Install Ubuntu Software
+
+Use `sudo apt-get install <package name>`.  As examples, this is how
+you would get GIT:
+
+    sudo apt-get install git
+
+This will get you a compiler for your host PC:
+
+    sudo apt-get install gcc
+
+This will get you an ARM compiler for your target:
+
+    sudo apt-get install gcc-arm-none-eabi
+
+**NOTE**: That is just an example.  I am not sure if apt-get will give you a
+current or usable compiler.  You should carefully select your toolchain
+for the needs of your project.
+
+You will also need to get the kconfig-frontends configuration as
+described below under *NuttX Configuration Tool*.  In order to build the
+kconfig-frontends configuration tool you will also need: `make`, `gperf`,
+`flex`, `bison`, and `libncurses-dev`.
+
+That is enough to do a basic NuttX build.
+
+### Integrating with Windows Tools
+
+If you want to integrate with Windows native tools, then you would need
+deal with the same kind of craziness as with integrating Cygwin with
+native toolchains, see the section *Cygwin Build Problems* below.
+
+However, there is currently no build support for using Windows native
+tools with Ubuntu under Windows.  This tool combination is made to work
+with Cygwin through the use of the `cygpath -w` tool that converts paths
+from say `/cydrive/c/Program Files` to `C:\Program Files`.  There is,
+however, no corresponding tool to convert `/mnt/c/Program Files` in the
+Ubuntu environment.
+
+### Graphics Support
+
+The Ubuntu version support by Microsoft is a command-line only version.
+There is no support for Linux graphics utilities.
+
+This limitation is not a limitation of Ubuntu, however, only in what
+Microsoft is willing to support.  If you install a X-Server, then you
+can also use basic graphics utilities.  See for example:
+
+  <http://www.howtogeek.com/261575/how-to-run-graphical-linux-desktop-applications-from-windows-10s-bash-shell/>
+
+Many Linux graphics programs would, however, also require a graphics
+framework like GTK or Qt.  So this might be a trip down the rabbit hole.
+
+### Using macOS
+
+You need to install at least the following tools specific to macOS.
+
+  * flock (used by APPDIR build logic)
+    
+A macOS port is available at: <https://github.com/discoteq/flock>
+  
+    brew tap discoteq/discoteq
+    brew install flock
+  
+  If you want to build the sim:
+
+  * Xcode (the native compiler and the rest of the toolchain)
+
+  * ELF toolchain (if you want to build modules for CONFIG_LIBC_MODLIB)
+
+    brew install x86_64-elf-gc
+
+# INSTALLATION
+
+There are two ways to get NuttX:  You may download released, stable
+tarballs from either the project website.  Or you may get NuttX by
+cloning the GIT repositories.  Let's consider the released tarballs
+first:
+
+## Download and Unpack
+
+Download and unpack the NuttX tarball.  If you are reading this, then
+you have probably already done that.  After unpacking, you will end
+up with a directory called nuttx-version (where version is the NuttX
+version number). You might want to rename that directory nuttx to
+match the various instructions in the documentation and some scripts
+in the source tree.
+
+  * Download location:
+  
+    <https://nuttx.apache.org/download/>
+  
+  * Legacy download locations:
+
+    <https://bitbucket.org/nuttx/nuttx/downloads>  
+    <https://sourceforge.net/projects/nuttx/files/nuttx/>
+
+## Semi-Optional apps/ Package
+
+All NuttX libraries and example code used to be in included within
+the NuttX source tree.  As of NuttX-6.0, this application code was
+moved into a separate tarball, the apps tarball.  If you are just
+beginning with NuttX, then you will want to download the versioned
+apps tarball along with the NuttX tarball.  If you already have your
+own product application directory, then you may not need the apps
+tarball.
+
+It is called "Semi-optional" because if you don't have some `apps/`
+directory, NuttX will *fail* to build! You do not necessarily need
+to use the NuttX apps tarball but may, instead, provide your own
+custom application directory.  Such a custom directory would need
+to include a valid Makefile to support the build and a valid Kconfig
+file to support the configuration.  More about these files later.
+
+Download then unpack the apps tarball in the same directory where you
+unpacked the NuttX tarball.  After you unpack the apps tarball, you
+will have a new directory called apps-version (where the version
+should exactly match the version of the NuttX tarball).  Again, you
+might want to rename the directory to simply apps/ to match what
+you read in the documentation
+
+After unpacking (and renaming) the apps tarball, you will have two
+directories side by side like this:
+
+             |
+        +----+----+
+        |         |
+      nuttx/     apps/
+
+This is important because the NuttX build will expect to find the
+apps directory in that (default) location.  That default location
+can be changed by modifying your NuttX configuration file, but that
+is another story.
+
+## Installation Directories with Spaces in the Path
+
+The nuttx build directory should reside in a path that contains no
+spaces in any higher level directory name.  For example, under
+Cygwin, your home directory might be formed from your first and last
+names like: `/home/First Last`. That will cause strange errors when
+the make system tries to build.
+
+[Actually, that problem is probably not too difficult to fix.  Some
+ Makefiles probably just need some paths within double quotes]
+
+I work around spaces in the home directory name, by creating a
+new directory that does not contain any spaces, such as `/home/nuttx`.
+Then I install NuttX in `/home/nuttx` and always build from
+`/home/nuttx/nuttx-code`.
+
+## Downloading from Repositories
+
+### Cloning the Repository
+
+**BEFORE** cloning repositories on any Windows platform do the following GIT
+command:
+
+    git config --global core.autocrlf false
+
+That will avoid conversions of linefeeds (newlines, \n) to carriage
+return plus linefeed sequences (\r\n)
+
+The current NuttX du jour is available in from a GIT repository.  Here are
+instructions for cloning the core NuttX RTOS (corresponding to the nuttx
+tarball discussed above):
+
+    git clone https://gitbox.apache.org/repos/asf/incubator-nuttx.git nuttx
+
+-or-
+
+    git clone https://github.com/apache/incubator-nuttx.git nuttx
+
+And the semi-optional apps/ application directory and be cloned like:
+
+    git clone https://gitbox.apache.org/repos/asf/incubator-nuttx-apps.git apps
+  
+-or-
+  
+    git clone https://github.com/apache/incubator-nuttx-apps.git apps
+
+That will give you the same directory structure like this:
+    
+             |
+        +----+----+
+        |         |
+      nuttx/     apps/
+
+### Configuring the Clones
+
+The following steps need to be performed for each of the repositories.
+After changing to the clone directory:
+
+Set your identity:
+
+    git config --global user.name "My Name"
+    git config --global user.email my.name@example.com
+  
+Colorized diffs are much easier to read:
+
+    git config --global color.branch auto
+    git config --global color.diff auto
+    git config --global color.interactive auto
+    git config --global color.status auto
+
+Checkout other settings
+
+    git config --list
+
+### Cloning NuttX Inside Cygwin
+
+If you are cloning the NuttX repository, it is recommended to avoid
+automatic end of lines conversions by git. These conversions may break
+some scripts like configure.sh. Before cloning, do the following:
+
+    git config --global core.autocrlf false
+
+## Related Repositories
+
+These are standalone repositories:
+
+  * <https://gitbox.apache.org/repos/asf/incubator-nuttx-apps>  
+    or  
+    <https://github.com/apache/incubator-nuttx-apps.git>
+    
+    This directory holds an optional package of applications and libraries
+    can be used with the NuttX RTOS.  There is a README.txt file there that
+    will provide more information about that package.
+
+  * <https://bitbucket.org/nuttx/nxwidgets>
+  
+    This is the NuttX C++ graphics support.  This includes NxWM, the tiny
+    NuttX Window Manager.
+
+  * <https://bitbucket.org/nuttx/uclibc>
+  
+    This repository contains a version of the uClibc++ C++ library.  This code
+    originates from <http://cxx.uclibc.org/> and has been adapted for NuttX by the
+    RGMP team (<http://rgmp.sourceforge.net/wiki/index.php/Main_Page>).
+
+  * <https://bitbucket.org/nuttx/buildroot>
+  
+    A environment that you can to use to build a custom, NuttX GNU toolchain.
+
+  * <https://bitbucket.org/nuttx/tools>
+  
+    There are snapshots of some tools here that you will need to work with
+    NuttX:  kconfig-frontends, genromfs, and others.
+
+## Notes about Header Files
+
+### Other C-Library Header Files
+
+When a GCC toolchain is built, it must be built against a C library.
+The compiler together with the contents of the C library completes the
+C language definition and provides the complete C development
+environment.  NuttX provides its own, built-in C library.  So the
+complete, consistent C language definition for use with NuttX comes from
+the combination of the compiler and the header files provided by the
+NuttX C library.
+
+When a GCC toolchain is built, it incorporates the C library header
+files into the compiler internal directories and, in this way, the C
+library really becomes a part of the toolchain.  If you use the NuttX
+buildroot toolchain as described below under "NuttX Buildroot
+Toolchain", your GCC toolchain will build against the NuttX C library
+and will incorporate the NuttX C library header files as part of the
+toolchain.
+
+If you use some other, third-party tool chain, this will not be the
+case, however.  Those toolchains were probably built against some
+other, incompatible C library distribution (such as newlib).  Those
+tools will have incorporated the incompatible C library header files
+as part of the toolchain.  These incompatible header files must *not*
+be used with NuttX because they will conflict with definitions in the
+NuttX built-in C-Library.  For such toolchains that include header
+files from a foreign C-Library, NuttX must be compiled without using
+the standard header files that are distributed with your toolchain.
+This prevents including conflicting, incompatible header files such
+as stdio.h.
+
+The math.h and stdarg.h are probably the two most trouble some header
+files to deal with.  These troublesome header files are discussed in
+more detail below.
+
+### Header Files Provided by Your Toolchain
+
+Certain header files, such as `setjmp.h`, `stdarg.h`, and `math.h`, may still
+be needed from your toolchain and your compiler may not, however, be able
+to find these if you compile NuttX without using standard header files
+(i.e., with `-nostdinc`).  If that is the case, one solution is to copy
+those header file from your toolchain into the NuttX include directory.
+
+### Duplicated Header Files
+
+There are also a few header files that can be found in the `nuttx/include`
+directory which are duplicated by the header files from your toolchain.
+stdint.h and stdbool.h are examples.  If you prefer to use the `stdint.h`
+and `stdbool.h` header files from your toolchain, those could be copied
+into the `nuttx/include/` directory. Using most other header files from
+your toolchain would probably cause errors.
+
+### math.h
+
+Even though you should not use a foreign C-Library, you may still need
+to use other, external libraries with NuttX.  In particular, you may
+need to use the math library, libm.a.  NuttX supports a generic, built-in
+math library that can be enabled using `CONFIG_LIBM=y`.  However, you may
+still want to use a higher performance external math library that has
+been tuned for your CPU.  Sometimes such tuned math libraries are
+bundled with your toolchain.
+
+The math library header file, `math.h`, is a then special case.  If you do
+nothing, the standard math.h header file that is provided with your
+toolchain will be used.
+
+If you have a custom, architecture specific math.h header file, then
+that header file should be placed at `arch/<cpu>/include/math.h`.  There
+is a stub `math.h` header file located at `include/nuttx/lib/math.h`.  This stub
+header file can be used to "redirect" the inclusion to an architecture-
+specific math.h header file.  If you add an architecture specific math.h
+header file then you should also define `CONFIG_ARCH_MATH_H=y` in your
+NuttX Configuration file.  If `CONFIG_ARCH_MATH_H` is selected, then the
+top-level Makefile will copy the stub math.h header file from
+`include/nuttx/lib/math.h` to `include/math.h` where it will become the system
+`math.h` header file.  The stub `math.h` header file does nothing other
+than to include that architecture-specific `math.h` header file as the
+system `math.h` header file.
+
+### float.h
+
+If you enable the generic, built-in math library, then that math library
+will expect your toolchain to provide the standard `float.h` header file.
+The float.h header file defines the properties of your floating point
+implementation.  It would always be best to use your toolchain's `float.h`
+header file but if none is available, a default `float.h` header file will
+be provided if this option is selected.  However, there is no assurance
+that the settings in this `float.h` are actually correct for your platform!
+
+### stdarg.h
+
+In most cases, the correct version of stdarg.h is the version provided
+with your toolchain.  However, sometimes there are issues with
+using your toolchains `stdarg.h`.  For example, it may attempt to draw in
+header files that do not exist in NuttX or perhaps the header files that
+it uses are not compatible with the NuttX header files.  In those cases,
+you can use an architecture-specific `stdarg.h` header file by defining
+`CONFIG_ARCH_STDARG_H=y`.
+
+See the discussion above for the `math.h` header.  This setting works
+exactly the same for the `stdarg.h` header file.
+
+# CONFIGURING NUTTX
+
+## Instantiating "Canned" Configurations
+
+### `configure.sh` and `configure.bat`
+
+"Canned" NuttX configuration files are retained in:
+
+    boards/<arch-name>/<chip-name>/<board-name>/configs/<config-dir>
+
+Where `<board-name>` is the name of your development board and `<config-dir>`
+is the name of the sub-directory containing a specific configuration for
+that board. `<arch-name>` and `<chip-name>` refer to characteristics of the
+MCU used on the board: `<arch-name>` is the CPU architecture implemented
+by the MCU; `<chip-name>` identifies the MCU chip family.  Only a few
+steps are required to instantiate a NuttX configuration, but to make the
+configuration even easier there are scripts available in the tools/
+sub-directory combines those simple steps into one command.
+
+There is one tool for use with any Bash-like shell that does configuration
+steps.  It is used as follows:
+
+    tools/configure.sh <board-name>:<config-dir>
+
+There is an alternative Windows batch file that can be used in the windows
+native environment like:
+
+    tools\configure.bat <board-name>:<config-dir>
+
+And, to make sure that other platforms are supported, there is also a
+C program at tools/configure.c that can be compiled to establish the
+board configuration.
+
+See `tools/README.txt` for more information about these scripts.
+
+General information about configuring NuttX can be found in:
+
+    {TOPDIR}/boards/README.txt
+    {TOPDIR}/boards/<arch-name>/<chip-name>/<board-name>/README.txt
+
+### The Hidden Configuration Scripts:
+
+As mentioned above, there are only a few simple steps to instantiating a
+NuttX configuration.  Those steps are hidden by the configuration scripts
+but are summarized below:
+  
+  1. Copy Files
+  
+     Configuring NuttX requires only copying two files from the
+     `<config-dir>` to the directory where you installed NuttX (TOPDIR):
+  
+       * Copy `boards/<arch-name>/<chip-name>/<board-name>/configs/<config-dir>/Make.def` to `{TOPDIR}/Make.defs`
+    
+         OR
+    
+       * Copy `boards/<arch-name>/<chip-name>/<board-name>/scripts/Make.def`
+         to `{TOPDIR}/Make.defs`
+    
+         Make.defs describes the rules needed by your tool chain to compile
+         and link code.  You may need to modify this file to match the
+         specific needs of your toolchain.  NOTE that a configuration may
+         have its own unique Make.defs file in its configuration directory or
+         it may use a common Make.defs file for the board in the scripts/
+         directory.  The first takes precedence.
+    
+       * Copy `boards/<arch-name>/<chip-name>/<board-name>/configs/<config-dir>/defconfig` to `{TOPDIR}/.config`
+    
+         The defconfig file holds the actual build configuration.  This
+         file is included by all other make files to determine what is
+         included in the build and what is not.  This file is also used
+         to generate a C configuration header at `include/nuttx/config.h`.
+    
+       * Copy other, environment-specific files to `{TOPDIR}`
+    
+         This might include files like .gdbinit or IDE configuration files
+         like .project or .cproject.
+  
+  2. Refresh the Configuration
+  
+     New configuration setting may be added or removed.  Existing settings
+     may also change there values or options.  This must be handled by
+     refreshing the configuration as described below.
+    
+     NOTE:  NuttX uses only compressed defconfig files.  For the NuttX
+     defconfig files, this refreshing step is *NOT* optional; it is also
+     necessary to uncompress and regenerate the full making file.  This is
+     discussed further below.
+
+## Refreshing Configurations
+
+Configurations can get out of date.  As new configuration settings are
+added or removed or as dependencies between configuration settings
+change, the contents of a default configuration can become out of synch
+with the build systems.  Hence, it is a good practice to "refresh" each
+configuration after configuring and before making.  To refresh the
+configuration, use the NuttX Configuration Tool like this:
+
+    make oldconfig
+
+AFTER you have instantiated the NuttX configuration as described above.
+The configuration step copied the .config file into place in the top-level
+NuttX directory; 'make oldconfig' step will then operate on that .config
+file to bring it up-to-date.
+
+If your configuration is out of date, you will be prompted by 'make oldconfig'
+to resolve the issues detected by the configuration tool, that is, to
+provide values for the new configuration options in the build system.  Doing
+this can save you a lot of problems down the road due to obsolete settings in
+the default board configuration file.  The NuttX configuration tool is
+discussed in more detail in the following paragraph.
+
+Confused about what the correct value for a new configuration item should
+be?  Enter ? in response to the 'make oldconfig' prompt and it will show
+you the help text that goes with the option.
+
+If you don't want to make any decisions are willing to just accept the
+recommended default value for each new configuration item, an even easier
+way is:
+
+    make olddefconfig
+
+The olddefconfig target will simply bring your configuration up to date with
+the current Kconfig files, setting any new options to the default value.
+No questions asked.
+
+## NuttX Configuration Tool
+
+An automated tool has been incorporated to support re-configuration
+of NuttX.  This tool is based on the kconfig-frontends application available
+at <https://bitbucket.org/nuttx/tools/src/master/kconfig-frontends/>.  (This
+is a snapshot of the old <http://ymorin.is-a-geek.org/projects/kconfig-frontends>
+which is no longer available.)  This application provides a tool called
+`kconfig-mconf` that is used by the NuttX top-level Makefile. The following
+make target is provided:
+
+    make menuconfig
+
+This make target will bring up NuttX configuration menus.
+
+**WARNING**:  Never do `make menuconfig` on a configuration that has
+not been converted to use the kconfig-frontends tools!  This will
+damage your configuration (see
+<http://www.nuttx.org/doku.php?id=wiki:howtos:convertconfig>).
+
+How do we tell a new configuration from an old one? See "Incompatibilities
+with Older Configurations" below.
+
+The `menuconfig` make target depends on two things:
+
+  1. The Kconfig configuration data files that appear in almost all
+     NuttX directories.  These data files are the part that is still
+     under development (patches are welcome!).  The Kconfig files
+     contain configuration information for the configuration settings
+     relevant to the directory in which the Kconfig file resides.
+     
+     NOTE: For a description of the syntax of this configuration file,
+     see kconfig-language.txt in the tools repository at
+     <https://bitbucket.org/nuttx/tools>
+  
+  2. The `kconfig-mconf` tool. `kconfig-mconf` is part of the
+     kconfig-frontends package.  You can download that package from the
+     snapshot in the tools repository at <https://bitbucket.org/nuttx/tools>.
+  
+     Building kconfig-frontends under Linux may be as simple as
+     `configure; make; make install` but there may be some build
+     complexities, especially if you are building under Cygwin.  See
+     the more detailed build instructions in the top-level README.txt
+     file of the tools repository at <https://bitbucket.org/nuttx/tools>.
+  
+  
+     The `make install` step will, by default, install the `kconfig-mconf`
+     tool at `/usr/local/bin/mconf`.  Where ever you choose to
+     install `kconfig-mconf`, make certain that your PATH variable includes
+     a path to that installation directory.
+  
+     The kconfig-frontends tools will not build in a native Windows
+     environment directly "out-of-the-box".  For the Windows native
+     case, you can use the modified version of kconfig-frontends
+     that can be found at
+
+     <http://uvc.de/posts/linux-kernel-configuration-tool-kconfig-under-windows.html>  
+
+     or a more recent port that can be found at  
+
+     <http://reclonelabs.com/more-kconfig-awesomeness-for-windows/>.
+   
+The basic configuration order is "bottom-up":
+   
+   - Select the build environment,
+   - Select the processor,
+   - Select the board,
+   - Select the supported peripherals
+   - Configure the device drivers,
+   - Configure the application options on top of this.
+   
+This is pretty straight forward for creating new configurations
+but may be less intuitive for modifying existing configurations.
+
+Another ncurses-based tool that is an option to kconfig-mconf is
+kconfig-nconf.  The differences are primary in in the aesthetics of the
+UI.  If you have kconfig-nconf built, then you can invoke that front end
+with:
+   
+     make nconfig
+   
+If you have an environment that supports the Qt or GTK graphical systems
+(probably KDE or gnome, respectively, or Cygwin under Windows with Qt or
+GTK installed), then you can also build the graphical kconfig-frontends,
+kconfig-qconf and kconfig-gconf.  In these case, you can start the
+graphical configurator with either:
+   
+     make qconfig
+   
+ or
+   
+     make gconfig
+   
+Some keyboard shortcuts supported by kconfig-mconf, the tool that runs
+when you do 'make menuconfig':
+
+   - `?` will bring up the mconfig help display.
+   
+   - `/` can be used find configuration selections.
+   
+   - `Z` can be used to reveal hidden configuration options
+   
+These last two shortcuts are described further in the following
+paragraphs.
+
+## Finding Selections in the Configuration Menus
+
+The NuttX configuration options have gotten complex and it can be very
+difficult to find options in the menu trees if you are not sure where
+to look.  The "basic configuration order" describe above can help to
+narrow things down.
+
+But if you know exactly what configuration setting you want to select,
+say CONFIG_XYZ, but not where to find it, then the 'make menuconfig'
+version of the tool offers some help:  By pressing the '/' key, the
+tool will bring up a menu that will allow you to search for a
+configuration item.  Just enter the string CONFIG_XYZ and press 'ENTER'.
+It will show you not only where to find the configuration item, but
+also all of the dependencies related to the configuration item.
+
+## Reveal Hidden Configuration Options
+
+If you type `Z`, then kconfig-mconf will change what is displayed.
+Normally, only enabled features that have all of their dependencies met
+are displayed.  That is, of course, not very useful if you would like to
+discover new options or if you are looking for an option and do not
+realize that the dependencies have not yet been selected and, hence, it
+is not displayed.
+
+But if you enter `Z`, then every option will be shown, whether or not its
+dependencies have been met.  You can then see everything that could be
+selected with the right dependency selections.  These additional options
+will be shown the `-` for the selection and for the value (since it
+cannot be selected and has no value).  About all you do is to select
+the `<Help>` option to see what the dependencies are.
+
+## Make Sure that You are on the Right Platform
+
+Saved configurations may run on Linux, Cygwin (32- or 64-bit), or other
+platforms.  The platform characteristics can be changed use `make
+menuconfig`.  Sometimes this can be confusing due to the differences
+between the platforms.  Enter sethost.sh
+
+sethost.sh is a simple script that changes a configuration to your
+host platform.  This can greatly simplify life if you use many different
+configurations.  For example, if you are running on Linux and you
+configure like this:
+
+    tools/configure.sh board:configuration
+
+The you can use the following command to both (1) make sure that the
+configuration is up to date, AND (2) the configuration is set up
+correctly for Linux:
+
+    tools/sethost.sh -l
+
+Or, if you are on a Windows/Cygwin 64-bit platform:
+
+    tools/sethost.sh -c
+
+Or, for MSYS/MSYS2:
+
+    tools/sethost.sh -g
+
+Other options are available from the help option built into the
+script.  You can see all options with:
+
+    tools/sethost.sh -h
+
+Recently, the options to the configure.sh (and configure.bat) scripts have
+been extended so that you both setup the configuration, select for the host
+platform that you use, and uncompress and refresh the defconfig file all in
+one command like:
+
+    tools/configure.sh -l board:configuration
+
+For a Linux host or for a Windows/Cygwin host:
+
+    tools/configure.sh -c board:configuration
+
+Other options are available from the help option built into the
+script.  You can see all options with:
+
+    tools/configure.sh -h
+
+## Comparing Two Configurations
+
+If you try to compare two configurations using 'diff', you will probably
+not be happy with the result.  There are superfluous things added to
+the configuration files that make comparisons with the human eye
+difficult.
+
+There is a tool at nuttx/tools/cmpconfig.c that can be built to simplify
+these comparisons.  The output from this difference tool will show only
+the meaningful differences between two configuration files.  This tool is
+built as follows:
+
+    cd nuttx/tools
+    make -f Makefile.host
+
+This will create a program called 'cmpconfig' or 'comconfig.exe' on Windows.
+
+Why would you want to compare two configuration files?  Here are a few
+of the reasons why I do this
+
+  1. When I create a new configuration I usually base it on an older
+     configuration and I want to know, "What are the options that I need to
+     change to add the new feature to the older configurations?"  For example,
+     suppose that I have a boardA/nsh configuration and I want to create a
+     boardA/nxwm configuration.  Suppose I already have boardB/nsh and
+     boardB/nxwm configurations.  Then by comparing the boardB/nsh with the
+     boardB/nxwm I can see the modifications that I would need to make to my
+     boardA/nsh to create a new  boardA/nxwm.
+  
+  2. But the most common reason that I use the 'cmpconfig' program is to
+     check the results of "refreshing" a configuration with 'make oldconfig'
+     (see the paragraph "Refreshing Configurations" above).  The 'make
+     oldconfig' command will make changes to my configuration and using
+     'cmpconfig', I can see precisely what those changes were and if any
+     should be of concern to me.
+  
+  3. The 'cmpconfig' tool can also be useful when converting older, legacy
+     manual configurations to the current configurations based on the
+     kconfig-frontends tools.  See the following paragraph.
+
+## Making defconfig Files
+
+### .config Files as defconfig Files:
+
+The minimum defconfig file is simply the generated .config file with
+CONFIG_APPS_DIR setting removed or commented out.  That setting provides
+the name and location of the apps/ directory relative to the nuttx build
+directory.  The default is ../apps/, however, the apps directory may be
+any other location and may have a different name.  For example, the name
+of versioned NuttX releases are always in the form apps-xx.yy where xx.yy
+is the version number.
+
+### Finding the apps/ Directory Path:
+
+When the default configuration is installed using one of the scripts or
+programs in the NuttX tools directory, there will be an option to provide
+the path to the apps/ directory.  If not provided, then the configure tool
+will look around and try to make a reasonable decision about where the
+apps/ directory is located.
+
+### Compressed defconfig Files:
+
+The Makefile also supports an option to generate very small defconfig
+files.  The .config files are quite large and complex.  But most of the
+settings in the .config file simply have the default settings from the
+Kconfig files.  These .config files can be converted into small defconfig
+file:
+    
+    make savedefconfig
+    
+That make target will generate a defconfig file in the top-level
+directory.  The size reduction is really quite remarkable:
+    
+    wc -l .config defconfig
+     1085 .config
+       82 defconfig
+     1167 total
+    
+In order to be usable, the .config file installed from the compressed
+defconfig file must be reconstituted using:
+    
+    make olddefconfig
+    
+  > **NOTE 1**:  Only compressed defconfig files are retained in the NuttX repository.
+  > All patches and PRs that attempt to add or modify a defconfig file MUST
+  > use the compressed defconfig format as created by 'make savdefconfig.'
+    
+  > **NOTE 2**:  When 'make savedefconfig' runs it will try several things some of
+  > which are expected to fail.  In these cases you will see an error message
+  > from make followed by "(ignored)."  You should also ignore these messages
+    
+**CAUTION**:  This size reduction was accomplished by removing all setting
+from the .config file that were at the default value.  'make olddefconfig'
+can regenerate the original .config file by simply restoring those default
+settings.  The underlying assumption here is, of course, that the default
+settings do not change.  If the default settings change, and they often
+do, then the original .config may not be reproducible.
+
+So if your project requires 100% reproducibility over a long period of
+time, you make want to save the complete .config files vs. the standard,
+compressed defconfig file.
+
+### Configuring with "Compressed" defconfig Files:
+
+As described above defconfig, all NuttX defconfig files are compressed
+using 'make savedeconfig'.  These compressed defconfig files are
+generally not fully usable as they are and may not build the target
+binaries that you want because the compression process removed all of
+the default settings from the defconfig file.  To restore the default
+settings, you should run the following after configuring:
+
+    make olddefconfig
+
+That will restore the the missing defaulted values.
+
+Using this command after configuring is generally a good practice anyway:
+Even if the defconfig files are not "compressed" in this fashion, the
+defconfig file may be old and the only way to assure that the installed
+.config is is up to date is via 'make oldconfig' or 'make olddefconfig'.
+See the paragraph above entitled ""Refreshing Configurations" for
+additional information.
+
+## Incompatibilities with Older Configurations
+
+**WARNING**
+
+The current NuttX build system supports *only* the new compressed,
+defconfig configuration files generated using the kconfig-frontends tools
+as described in the preceding section.  Support for the older, legacy,
+manual configurations was eliminated in NuttX 7.0; support for
+uncompressed .config-files-as-defconfig files was eliminated after
+NuttX-7.21.  All configurations must now be done using the
+kconfig-frontends tool.  The older manual configurations and the new
+kconfig-frontends configurations are not compatible.  Old legacy
+configurations can *not* be used with the kconfig-frontends tool and,
+hence, cannot be used with releases of NuttX 7.0 and beyond:
+
+If you run 'make menuconfig' with a legacy configuration the resulting
+configuration will probably not be functional.
+
+  > Q: How can I tell if a configuration is a new kconfig-frontends
+  >   configuration or an older, manual configuration?
+  >
+  > A: Only old, manual configurations will have an appconfig file
+  > 
+  > Q: How can I convert a older, manual configuration into a new,
+  >    kconfig-frontends toolchain.
+  >
+  > A: Refer to <http://www.nuttx.org/doku.php?id=wiki:howtos:convertconfig>
+  
+**WARNING**
+
+As described above, whenever you use a configuration, you really should
+always refresh the configuration with the following command *before* you
+make NuttX:
+
+    make oldconfig
+
+OR
+
+    make olddefconfig
+
+This will make sure that the configuration is up-to-date in the event that
+it has lapsed behind the current NuttX development (see the paragraph
+"Refreshing Configurations" above).  But this only works with *new*
+configuration files created with the kconfig-frontends tools.
+
+Further, this step is *NOT* optional with the new, compressed defconfig
+files.  It is a necessary step that will also uncompress the defconfig
+file, regenerating the .config and making it usable for NuttX builds.
+
+Never do `make oldconfig` (OR `make menuconfig`) on a  configuration that
+has not been converted to use the kconfig-frontends tools!  This will
+damage your configuration (see
+<http://www.nuttx.org/doku.php?id=wiki:howtos:convertconfig>).
+
+## NuttX Configuration Tool under DOS
+
+  Recent versions of NuttX support building NuttX from a native Windows
+  console window (see *Native Windows Build* below).  But kconfig-frontends
+  is a Linux tool.  At one time this was a problem for Windows users, but
+  now there are two specially modified versions of the kconfig-frontends
+  tools that can be used.  One can be found here:
+  <http://uvc.de/posts/linux-kernel-configuration-tool-kconfig-under-windows.html>
+
+  The configuration steps of the most recent versions of NuttX require the
+  kconfig-tweak tool that is not not available in the the above.  However,
+  there has been an update to this Kconfig Windows tools that does include
+  kconfig-tweak:  http://reclonelabs.com/more-kconfig-awesomeness-for-windows/
+
+  Source code is available here: <https://github.com/reclone/kconfig-frontends-win32>
+  and <https://github.com/reclone/kconfig-frontends-win32/releases>
+
+  It is also possible to use the version of kconfig-frontends built
+  under Cygwin outside of the Cygwin "sandbox" in a native Windows
+  environment:
+
+  1. You can run the configuration tool using Cygwin.  However, the
+     Cygwin Makefile.win will complain so to do this will, you have
+     to manually edit the .config file:
+     
+     a. Delete the line: CONFIG_WINDOWS_NATIVE=y

Review comment:
       ```suggestion
        a. Delete the line: `CONFIG_WINDOWS_NATIVE=y`
   ```

##########
File path: README.md
##########
@@ -0,0 +1,2513 @@
+# APACHE NUTTX (INCUBATING)
+
+* Introduction
+  - Incubation Status
+* Community
+  - Getting Help
+  - Mailing Lists
+  - Issue Tracker
+  - Source Code
+  - Website Source Code
+* Environments
+  - Installing Cygwin
+  - Ubuntu Bash under Windows 10
+  - Using macOS
+* Installation
+  - Download and Unpack
+  - Semi-Optional apps/ Package
+  - Installation Directories with Spaces in the Path
+  - Downloading from Repositories
+  - Related Repositories
+  - Notes about Header Files
+* Configuring NuttX
+  - Instantiating "Canned" Configurations
+  - Refreshing Configurations
+  - NuttX Configuration Tool
+  - Finding Selections in the Configuration Menus
+  - Reveal Hidden Configuration Options
+  - Make Sure that You are on the Right Platform
+  - Comparing Two Configurations
+  - Making defconfig Files
+  - Incompatibilities with Older Configurations
+  - NuttX Configuration Tool under DOS
+* Toolchains
+  - Cross-Development Toolchains
+  - NuttX Buildroot Toolchain
+* Shells
+* Building NuttX
+  - Building
+  - Re-building
+  - Build Targets and Options
+  - Native Windows Build
+  - Installing GNUWin32
+* Cygwin Build Problems
+  - Strange Path Problems
+  - Window Native Toolchain Issues
+* Documentation
+
+# INTRODUCTION
+
+Apache NuttX (Incubating) is a real-time operating system (RTOS) with an
+emphasis on standards compliance and small footprint.  Scalable from 8-bit
+to 32-bit microcontroller environments, the primary governing standards in
+NuttX are POSIX and ANSI standards. Additional standard APIs from Unix and
+other common RTOSs (such as VxWorks) are adopted for functionality not
+available under these standards, or for functionality that is not
+appropriate for deeply-embedded environments (such as fork()).
+
+Extensive documentation can be found on the project wiki:
+  <https://cwiki.apache.org/NUTTX/Nuttx>
+
+## Incubation Status
+
+Apache NuttX (Incubating) is an effort undergoing Incubation at The Apache
+Software Foundation (ASF), sponsored by the Incubator.  For more on our
+incubation effort, please see the file DISCLAIMER-WIP, in the same
+directory as this README.
+
+For brevity, the rest of this file will refer to it as Apache NuttX or
+simply NuttX.
+
+# COMMUNITY
+
+Every volunteer project obtains its strength from the people involved in
+it.  We invite you to participate as much or as little as you choose.
+
+We encourage you to:
+
+  - Use our project and provide feedback.
+  - Provide us with use-cases.
+  - Report bugs and submit patches.
+  - Contribute code or documentation.
+
+## Getting Help
+
+The best place to get help is the developer's mailing list.  Please see
+the following section:
+
+## Mailing Lists
+
+Get help using NuttX or contribute to the project on our mailing lists:
+
+  * <de...@nuttx.apache.org> is for people who want to contribute code to NuttX.
+    * To subscribe, send an email to <de...@nuttx.apache.org>.
+    * To unsubscribe, send an email to <de...@nuttx.apache.org>.
+    * View the archives at:
+      <https://www.mail-archive.com/dev@nuttx.apache.org/>
+
+  * <co...@nuttx.apache.org> is a read-only list that notifies subscribers
+  about commit messages and patches to NuttX.
+    * To subscribe, send an email to <co...@nuttx.apache.org>.
+    * To unsubscribe, send an email to <co...@nuttx.apache.org>.
+    * View the archives at:
+      <https://www.mail-archive.com/commits@nuttx.apache.org/>
+
+## Issue Tracker
+
+### Bug Reports:
+
+Found bug? Send an email to the dev list: <de...@nuttx.apache.org>
+
+Before submitting an issue, please:
+
+  - Verify that the bug does in fact exist. 
+  
+  - Search the mailing list archives to verify there is no existing issue
+    reporting the bug you've found.
+ 
+  - Consider tracking down the bug yourself in the NuttX source code and
+    submitting a patch along with your bug report.  This is a great time
+    saver for the NuttX developers and helps ensure the bug will be fixed
+    quickly.
+  
+### Feature Requests:
+  
+Enhancement requests for new features are also welcome. The more concrete
+and rational the request is, the greater the chance it will incorporated
+into future releases.
+
+## Source Code
+
+The project sources are in two Git repositories.  The core OS is in
+incubator-nuttx and the apps repository is in incubator-nuttx-apps.  These
+are housed in GitBox on ASF servers and also mirrored at GitHub.  These
+are kept in sync, so you can use whichever option you prefer.
+
+  - NuttX core OS repository:
+    
+    - Primary:
+      <https://gitbox.apache.org/repos/asf?p=incubator-nuttx.git>
+    
+    - GitHub Mirror:
+      <https://github.com/apache/incubator-nuttx>
+  
+  - Apps repository:
+    
+    - Primary:
+      <https://gitbox.apache.org/repos/asf?p=incubator-nuttx-apps.git>
+    
+    - GitHub Mirror:
+      <https://github.com/apache/incubator-nuttx-apps>
+
+## Website Source Code
+
+The project website sources are accessible via the website source code
+  repository which is also mirrored in GitHub:
+
+- Primary:
+  <https://gitbox.apache.org/repos/asf?p=incubator-nuttx-website.git>
+
+- GitHub Mirror:
+  <https://github.com/apache/incubator-nuttx-website>
+
+# ENVIRONMENTS
+
+  NuttX requires a POSIX development environment such as you would find under
+  Linux or macOS.  NuttX may also be installed and built on Windows system
+  if you also provide such a POSIX development environment.  Options for a
+  POSIX development environment under Windows include:
+
+  - An installation of Linux on a virtual machine (VM) in Windows.  I have
+    not been happy using a VM myself.  I have had stability problems with
+    open source VMs and commercial VMs cost more than I want to spend.
+    Sharing files with Linux running in a VM is awkward;  sharing devices
+    connected to the Windows box with Linux in a VM is, at the very least,
+    confusing;  Using Windows tools (such as Segger J-Link) with files
+    built under the Linux VM is not a possibility.
+
+  - The Cygwin environment.  Instructions for installation of Cygwin on a
+    Windows system are provided in the following paragraph, "Installing
+    Cygwin".  Cygwin is a mature, well-tested, and very convenient
+    environment.  It is especially convenient if you  need to
+    integrate with Windows tools and files.  Downsides are that the
+    installation time is very long and the compile times are slow.
+
+  - Ubuntu/Bash shell under Windows 10.  This is a new option under
+    Windows 10.  See the section "Ubuntu Bash under Windows 10" below.
+    This is an improvement over Cygwin if your concern is compile time;
+    its build performance is comparable to native Linux, certainly better
+    than the Cygwin build time.  It also installs in a tiny fraction of
+    the time as Cygwin, perhaps 20 minutes for the basic Ubuntu install
+    (vs. more than a day for the complete Cygwin install).
+  
+    There have been even more recent ports of Linux environment to
+    Windows.  I need to update this section to include some mention of
+    these alternatives.
+
+  - The MSYS environment.  MSYS derives from an older version of Cygwin
+    simplified and adapted to work more naturally in the Windows
+    environment.  See <http://www.mingw.org/wiki/MSYS> if you are
+    interested in using MSYS.  The advantages of the MSYS environment is
+    that it is better integrted with the native Windows environment and
+    lighter weight; it uses only a  minimal number of add-on POSIX-land
+    tools.
+  
+    The download link in that Wiki takes you to the SourceForge download
+    site.  The SourceForge MSYS project has been stagnant for some time.
+    The MSYS project has more recently moved to
+    <http://odsn.net/projects/sfnet_mingwbundle>.  Downloads of current .zip
+    files are available there but no instructions for the installation.
+
+  - MSYS2 appears to be a re-write of MSYS based on a newer version of
+    Cygwin.  Is it available at <https://www.msys2.org>.  A windows
+    installer is available at that site along with very good installation
+    instructions.  The download is relatively quick (at least compared to
+    Cygwin) and the 'pacman' package management tool supports supports
+    simple system updates.  For example, 'pacman -S git' will install the
+    GIT command line utilities.
+
+  - Other POSIX environments.  Check out:
+    
+    - UnxUtils: <https://sourceforge.net/projects/unxutils/>,
+      <https://en.wikipedia.org/wiki/UnxUtils>
+    - MobaXterm: <https://mobaxterm.mobatek.net/>
+    - Gow: <https://github.com/bmatzelle/gow/wiki>
+  
+    **Disclaimer**:  In principle, these should work.  However, I have never
+    used any of these environments and cannot guarantee that there is
+    not some less-than-obvious issues.
+  
+NuttX can also be installed and built on a native Windows system, but with
+some potential tool-related issues (see the discussion "Native Windows
+Build" under "Building NuttX" below).  GNUWin32 is used to provide
+compatible native windows tools.
+
+## Installing Cygwin
+
+Installing Cygwin on your Windows PC is simple, but time consuming.  See
+<http://www.cygwin.com/> for installation instructions. Basically you just
+need to download a tiny setup.exe program and it does the real, network
+installation for you.
+
+Some Cygwin installation tips:
+
+  1. Install at `C:\cygwin`
+  
+  2. Install **everything**:  "Only the minimal base packages from the
+     Cygwin distribution are installed by default. Clicking on categories
+     and packages in the setup.exe package installation screen will
+     provide you with the ability to control what is installed or updated.
+     Clicking on the "Default" field next to the "All" category will
+     provide you with the opportunity to install every Cygwin package.
+     Be advised that this will download and install hundreds of megabytes
+     to your computer."
+   
+If you use the "default" installation, you will be missing many
+of the Cygwin utilities that you will need to build NuttX.  The
+build will fail in numerous places because of missing packages.
+
+NOTE: The last time I installed **everything**, the download was
+about 5GiB.  The server I selected was also very slow so it took
+over a day to do the whole install!
+
+NOTE: You don't really have to install **everything** but I cannot
+answer the question "Then what should I install?"  I don't know
+the answer to that and so will continue to recommend installing
+**everything**.
+
+You should certainly be able to omit "Science", "Math", and
+"Publishing".  You can try omitting KDE, Gnome, GTK, and other
+graphics packages if you don't plan to use them.
+
+Perhaps a minimum set would be those packages listed below for the
+"Ubuntu Bash under Windows 10" installation?
+
+**UPDATE**:  Sergey Frolov had success with the following minimal
+Cygwin configuration:
+   
+   1. After starting the Cygwin installer, keep the recommended
+      packages that are pre-selected in the default configuration.
+   
+   2. Using the installation tools, add the following packages:
+      
+        make (GNU make)  bison        libgmp3-dev
+        gcc-core         byacc        libmpfr-dev
+        gcc-g++          gperf        libmpc-dev
+        flex             gdb          automake-1.15
+        libncurses-dev   libgmp-dev
+   
+After installing Cygwin, you will get lots of links for installed
+tools and shells.  I use the RXVT native shell.  It is fast and reliable
+and does not require you to run the Cygwin X server (which is neither
+fast nor reliable).  Unless otherwise noted, the rest of these
+instructions assume that you are at a bash command line prompt in
+either Linux or in Cygwin shell.
+
+## Using MSYS
+
+MSYS is an environment the derives from Cygwin.  Thus, most things said
+about Cygwin apply equally to MSYS.  This section will, then, focus on
+the differences when using MSYS, specifically MSYS2.
+
+Here is it assumed that you have already downloaded and installed MSYS2
+from https://www.msys2.org using the windows installer available at that
+location.  It is also assumed that you have brought in the necessary
+tools using the 'pacman' package management tool Tools needed including:
+
+  pacman -S git
+  pacman -S make
+  pacman -S gcc
+  pacman -S gdb
+
+And possibly others depending upon your usage.  Then you will need to
+build and install kconfig-frontends per the instructions of the top-level
+README.txt file in the tools repository.  This requires the following
+additional tools:
+
+    pacman -S bison
+    pacman -S gperf
+    pacman -S ncurses-devel
+    pacman -S automake-wrapper
+    pacman -S autoconf
+    pacman -S pkg-config
+
+Because of some versioning issues, I had to run 'aclocal' prior to
+running the kconfig-frontends configure script.  See "Configuring NuttX"
+below for further information.
+
+Unlike Cygwin, MSYS does not support symbolic links.  The 'ln -s' command
+will, in fact, copy a directory!  This means that you Make.defs file will
+have to include definitions like:
+
+    ifeq ($(CONFIG_WINDOWS_MSYS),y)
+      DIRLINK = $(TOPDIR)/tools/copydir.sh
+      DIRUNLINK = $(TOPDIR)/tools/unlink.sh
+    endif
+
+This will force the directory copies to work in a way that can be handled
+by the NuttX build system.  NOTE:  The default link.sh script has been
+updated so that is should now be MSYS2 compatible.  The above is preferred
+but no longer necessary in the Make.defs file.
+
+To build the simulator under MSYS, you also need:
+
+    pacman -S zlib-devel
+
+It appears that you cannot use directory names with spaces in them like
+"/c/Program\ Files \(86\)" in the MSYS path variable.  I worked around this
+by create Windows junctions like this:
+
+  1. Open the a windows command terminal,
+  
+  2. CD to `c:\msys64`, then
+  
+  3. `mklink /j programfiles "C:/Program\ Files"` and
+  
+  4. `mklink /j programfiles86 "C:/Program\ Files\ \(x86\)"`
+     
+     They then show up as `/programfiles` and `/programfiles86` with the MSYS2
+     sandbox.  Those paths can then be used with the PATH variable.  I had
+     to do something similar for the path to the GNU Tools "ARM Embedded
+     Toolchain" which also has spaces in the path name.
+
+## Ubuntu Bash under Windows 10
+
+A better version of a command-line only Ubuntu under Windows 10 (beta)
+has recently been made available from Microsoft.
+
+### Installation
+
+Installation instructions abound on the Internet complete with screen
+shots.  I will attempt to duplicate those instructions in full here.
+Here are the simplified installation steps:
+
+  - Open *Settings*.
+  
+  - Click on *Update & security*.
+  
+  - Click on *For Developers*.
+  
+  - Under *Use developer features*, select the *Developer mode* option to
+    setup the environment to install Bash.
+  
+  - A message box should pop up.  Click *Yes* to turn on developer mode.
+  
+  - After the necessary components install, you'll need to restart your
+    computer.
+    
+    Once your computer reboots:
+  
+  - Open *Control Panel*.
+  
+  - Click on *Programs*.
+  
+  - Click on *Turn Windows features on or off*.
+  
+  - A list of features will pop up, check the *Windows Subsystem for Linux
+    (beta)* option.
+  
+  - Click *OK*.
+  
+  - Once the components installed on your computer, click the *Restart
+    now* button to complete the task.
+    
+    After your computer restarts, you will notice that Bash will not appear in
+    the *Recently added* list of apps, this is because Bash isn't actually
+    installed yet. Now that you have setup the necessary components, use the
+    following steps to complete the installation of Bash:
+  
+  - Open *Start*, do a search for `bash.exe`, and press *Enter*.
+  
+  - On the command prompt, type `y` and press Enter to download and install
+    Bash from the Windows Store.  This will take awhile.
+  
+  - Then you'll need to create a default UNIX user account. This account
+    doesn't have to be the same as your Windows account. Enter the
+    username in the required field and press Enter (you can't use the
+    username `admin`).
+  
+  - Close the `bash.exe` command prompt.
+  
+  Now that you completed the installation and setup, you can open the Bash
+  tool from the Start menu like you would with any other app.
+
+### Accessing Windows Files from Ubuntu
+
+File systems will be mounted under `/mnt` so for example `C:\Program Files`
+appears at `/mnt/c/Program Files`.  This is as opposed to Cygwin where
+the same directory would appear at `/cygdrive/c/Program Files`.
+
+With these differences (perhaps a few other Windows quirks) the Ubuntu
+install works just like Ubuntu running natively on your PC.
+
+A good tip for file sharing is to use symbolic links within your Ubuntu
+home directory.  For example, suppose you have your `projects` directory
+at `C:\Documents\projects`.  Then you can set up a link to the `projects/`
+directory in your Ubuntu directory like:
+
+    ln -s /mnt/c/Documents/projects projects
+
+### Accessing Ubuntu Files From Windows
+
+In Ubuntu Userspace for Windows, the Ubuntu file system root directory is
+at:
+
+    %localappdata%\lxss\rootfs
+
+Or
+
+    C:\Users\Username\AppData\Local\lxss\rootfs
+
+However, I am unable to see my files under the rootfs\home directory.
+After some looking around, I find the home directory
+`%localappdata%\lxss\home`.
+
+With that trick access to the `/home` directory, you should actually be
+able to use Windows tools outside of the Ubuntu sandbox with versions of
+NuttX built within the sandbox using that path.
+
+### Executing Windows Tools from Ubuntu
+
+You can also execute Windows tools from within the Ubuntu sandbox:
+
+    /mnt/c/Program\ Files\ \(x86\)/Microchip/xc32/v1.43/bin/xc32-gcc.exe --version
+    Unable to translate current working directory. Using C:\WINDOWS\System32
+    xc32-gcc.exe (Microchip Technology) 4.8.3 MPLAB XC32 Compiler v1.43 Build date: Mar  1 2017
+    ...
+
+The error message indicates that there are more issues:  You cannot mix
+Windows tools that use Windows style paths in an environment that uses
+POSIX paths.  I think you would have to use Linux tools only from within
+the Ubuntu sandbox.
+
+### Install Ubuntu Software
+
+Use `sudo apt-get install <package name>`.  As examples, this is how
+you would get GIT:
+
+    sudo apt-get install git
+
+This will get you a compiler for your host PC:
+
+    sudo apt-get install gcc
+
+This will get you an ARM compiler for your target:
+
+    sudo apt-get install gcc-arm-none-eabi
+
+**NOTE**: That is just an example.  I am not sure if apt-get will give you a
+current or usable compiler.  You should carefully select your toolchain
+for the needs of your project.
+
+You will also need to get the kconfig-frontends configuration as
+described below under *NuttX Configuration Tool*.  In order to build the
+kconfig-frontends configuration tool you will also need: `make`, `gperf`,
+`flex`, `bison`, and `libncurses-dev`.
+
+That is enough to do a basic NuttX build.
+
+### Integrating with Windows Tools
+
+If you want to integrate with Windows native tools, then you would need
+deal with the same kind of craziness as with integrating Cygwin with
+native toolchains, see the section *Cygwin Build Problems* below.
+
+However, there is currently no build support for using Windows native
+tools with Ubuntu under Windows.  This tool combination is made to work
+with Cygwin through the use of the `cygpath -w` tool that converts paths
+from say `/cydrive/c/Program Files` to `C:\Program Files`.  There is,
+however, no corresponding tool to convert `/mnt/c/Program Files` in the
+Ubuntu environment.
+
+### Graphics Support
+
+The Ubuntu version support by Microsoft is a command-line only version.
+There is no support for Linux graphics utilities.
+
+This limitation is not a limitation of Ubuntu, however, only in what
+Microsoft is willing to support.  If you install a X-Server, then you
+can also use basic graphics utilities.  See for example:
+
+  <http://www.howtogeek.com/261575/how-to-run-graphical-linux-desktop-applications-from-windows-10s-bash-shell/>
+
+Many Linux graphics programs would, however, also require a graphics
+framework like GTK or Qt.  So this might be a trip down the rabbit hole.
+
+### Using macOS
+
+You need to install at least the following tools specific to macOS.
+
+  * flock (used by APPDIR build logic)
+    
+A macOS port is available at: <https://github.com/discoteq/flock>
+  
+    brew tap discoteq/discoteq
+    brew install flock
+  
+  If you want to build the sim:
+
+  * Xcode (the native compiler and the rest of the toolchain)
+
+  * ELF toolchain (if you want to build modules for CONFIG_LIBC_MODLIB)
+
+    brew install x86_64-elf-gc
+
+# INSTALLATION
+
+There are two ways to get NuttX:  You may download released, stable
+tarballs from either the project website.  Or you may get NuttX by
+cloning the GIT repositories.  Let's consider the released tarballs
+first:
+
+## Download and Unpack
+
+Download and unpack the NuttX tarball.  If you are reading this, then
+you have probably already done that.  After unpacking, you will end
+up with a directory called nuttx-version (where version is the NuttX
+version number). You might want to rename that directory nuttx to
+match the various instructions in the documentation and some scripts
+in the source tree.
+
+  * Download location:
+  
+    <https://nuttx.apache.org/download/>
+  
+  * Legacy download locations:
+
+    <https://bitbucket.org/nuttx/nuttx/downloads>  
+    <https://sourceforge.net/projects/nuttx/files/nuttx/>
+
+## Semi-Optional apps/ Package
+
+All NuttX libraries and example code used to be in included within
+the NuttX source tree.  As of NuttX-6.0, this application code was
+moved into a separate tarball, the apps tarball.  If you are just
+beginning with NuttX, then you will want to download the versioned
+apps tarball along with the NuttX tarball.  If you already have your
+own product application directory, then you may not need the apps
+tarball.
+
+It is called "Semi-optional" because if you don't have some `apps/`
+directory, NuttX will *fail* to build! You do not necessarily need
+to use the NuttX apps tarball but may, instead, provide your own
+custom application directory.  Such a custom directory would need
+to include a valid Makefile to support the build and a valid Kconfig
+file to support the configuration.  More about these files later.
+
+Download then unpack the apps tarball in the same directory where you
+unpacked the NuttX tarball.  After you unpack the apps tarball, you
+will have a new directory called apps-version (where the version
+should exactly match the version of the NuttX tarball).  Again, you
+might want to rename the directory to simply apps/ to match what
+you read in the documentation
+
+After unpacking (and renaming) the apps tarball, you will have two
+directories side by side like this:
+
+             |
+        +----+----+
+        |         |
+      nuttx/     apps/
+
+This is important because the NuttX build will expect to find the
+apps directory in that (default) location.  That default location
+can be changed by modifying your NuttX configuration file, but that
+is another story.
+
+## Installation Directories with Spaces in the Path
+
+The nuttx build directory should reside in a path that contains no
+spaces in any higher level directory name.  For example, under
+Cygwin, your home directory might be formed from your first and last
+names like: `/home/First Last`. That will cause strange errors when
+the make system tries to build.
+
+[Actually, that problem is probably not too difficult to fix.  Some
+ Makefiles probably just need some paths within double quotes]
+
+I work around spaces in the home directory name, by creating a
+new directory that does not contain any spaces, such as `/home/nuttx`.
+Then I install NuttX in `/home/nuttx` and always build from
+`/home/nuttx/nuttx-code`.
+
+## Downloading from Repositories
+
+### Cloning the Repository
+
+**BEFORE** cloning repositories on any Windows platform do the following GIT
+command:
+
+    git config --global core.autocrlf false
+
+That will avoid conversions of linefeeds (newlines, \n) to carriage
+return plus linefeed sequences (\r\n)
+
+The current NuttX du jour is available in from a GIT repository.  Here are
+instructions for cloning the core NuttX RTOS (corresponding to the nuttx
+tarball discussed above):
+
+    git clone https://gitbox.apache.org/repos/asf/incubator-nuttx.git nuttx
+
+-or-
+
+    git clone https://github.com/apache/incubator-nuttx.git nuttx
+
+And the semi-optional apps/ application directory and be cloned like:
+
+    git clone https://gitbox.apache.org/repos/asf/incubator-nuttx-apps.git apps
+  
+-or-
+  
+    git clone https://github.com/apache/incubator-nuttx-apps.git apps
+
+That will give you the same directory structure like this:
+    
+             |
+        +----+----+
+        |         |
+      nuttx/     apps/
+
+### Configuring the Clones
+
+The following steps need to be performed for each of the repositories.
+After changing to the clone directory:
+
+Set your identity:
+
+    git config --global user.name "My Name"
+    git config --global user.email my.name@example.com
+  
+Colorized diffs are much easier to read:
+
+    git config --global color.branch auto
+    git config --global color.diff auto
+    git config --global color.interactive auto
+    git config --global color.status auto
+
+Checkout other settings
+
+    git config --list
+
+### Cloning NuttX Inside Cygwin
+
+If you are cloning the NuttX repository, it is recommended to avoid
+automatic end of lines conversions by git. These conversions may break
+some scripts like configure.sh. Before cloning, do the following:
+
+    git config --global core.autocrlf false
+
+## Related Repositories
+
+These are standalone repositories:
+
+  * <https://gitbox.apache.org/repos/asf/incubator-nuttx-apps>  
+    or  
+    <https://github.com/apache/incubator-nuttx-apps.git>
+    
+    This directory holds an optional package of applications and libraries
+    can be used with the NuttX RTOS.  There is a README.txt file there that
+    will provide more information about that package.
+
+  * <https://bitbucket.org/nuttx/nxwidgets>
+  
+    This is the NuttX C++ graphics support.  This includes NxWM, the tiny
+    NuttX Window Manager.
+
+  * <https://bitbucket.org/nuttx/uclibc>
+  
+    This repository contains a version of the uClibc++ C++ library.  This code
+    originates from <http://cxx.uclibc.org/> and has been adapted for NuttX by the
+    RGMP team (<http://rgmp.sourceforge.net/wiki/index.php/Main_Page>).
+
+  * <https://bitbucket.org/nuttx/buildroot>
+  
+    A environment that you can to use to build a custom, NuttX GNU toolchain.
+
+  * <https://bitbucket.org/nuttx/tools>
+  
+    There are snapshots of some tools here that you will need to work with
+    NuttX:  kconfig-frontends, genromfs, and others.
+
+## Notes about Header Files
+
+### Other C-Library Header Files
+
+When a GCC toolchain is built, it must be built against a C library.
+The compiler together with the contents of the C library completes the
+C language definition and provides the complete C development
+environment.  NuttX provides its own, built-in C library.  So the
+complete, consistent C language definition for use with NuttX comes from
+the combination of the compiler and the header files provided by the
+NuttX C library.
+
+When a GCC toolchain is built, it incorporates the C library header
+files into the compiler internal directories and, in this way, the C
+library really becomes a part of the toolchain.  If you use the NuttX
+buildroot toolchain as described below under "NuttX Buildroot
+Toolchain", your GCC toolchain will build against the NuttX C library
+and will incorporate the NuttX C library header files as part of the
+toolchain.
+
+If you use some other, third-party tool chain, this will not be the
+case, however.  Those toolchains were probably built against some
+other, incompatible C library distribution (such as newlib).  Those
+tools will have incorporated the incompatible C library header files
+as part of the toolchain.  These incompatible header files must *not*
+be used with NuttX because they will conflict with definitions in the
+NuttX built-in C-Library.  For such toolchains that include header
+files from a foreign C-Library, NuttX must be compiled without using
+the standard header files that are distributed with your toolchain.
+This prevents including conflicting, incompatible header files such
+as stdio.h.
+
+The math.h and stdarg.h are probably the two most trouble some header
+files to deal with.  These troublesome header files are discussed in
+more detail below.
+
+### Header Files Provided by Your Toolchain
+
+Certain header files, such as `setjmp.h`, `stdarg.h`, and `math.h`, may still
+be needed from your toolchain and your compiler may not, however, be able
+to find these if you compile NuttX without using standard header files
+(i.e., with `-nostdinc`).  If that is the case, one solution is to copy
+those header file from your toolchain into the NuttX include directory.
+
+### Duplicated Header Files
+
+There are also a few header files that can be found in the `nuttx/include`
+directory which are duplicated by the header files from your toolchain.
+stdint.h and stdbool.h are examples.  If you prefer to use the `stdint.h`
+and `stdbool.h` header files from your toolchain, those could be copied
+into the `nuttx/include/` directory. Using most other header files from
+your toolchain would probably cause errors.
+
+### math.h
+
+Even though you should not use a foreign C-Library, you may still need
+to use other, external libraries with NuttX.  In particular, you may
+need to use the math library, libm.a.  NuttX supports a generic, built-in
+math library that can be enabled using `CONFIG_LIBM=y`.  However, you may
+still want to use a higher performance external math library that has
+been tuned for your CPU.  Sometimes such tuned math libraries are
+bundled with your toolchain.
+
+The math library header file, `math.h`, is a then special case.  If you do
+nothing, the standard math.h header file that is provided with your
+toolchain will be used.
+
+If you have a custom, architecture specific math.h header file, then
+that header file should be placed at `arch/<cpu>/include/math.h`.  There
+is a stub `math.h` header file located at `include/nuttx/lib/math.h`.  This stub
+header file can be used to "redirect" the inclusion to an architecture-
+specific math.h header file.  If you add an architecture specific math.h
+header file then you should also define `CONFIG_ARCH_MATH_H=y` in your
+NuttX Configuration file.  If `CONFIG_ARCH_MATH_H` is selected, then the
+top-level Makefile will copy the stub math.h header file from
+`include/nuttx/lib/math.h` to `include/math.h` where it will become the system
+`math.h` header file.  The stub `math.h` header file does nothing other
+than to include that architecture-specific `math.h` header file as the
+system `math.h` header file.
+
+### float.h
+
+If you enable the generic, built-in math library, then that math library
+will expect your toolchain to provide the standard `float.h` header file.
+The float.h header file defines the properties of your floating point
+implementation.  It would always be best to use your toolchain's `float.h`
+header file but if none is available, a default `float.h` header file will
+be provided if this option is selected.  However, there is no assurance
+that the settings in this `float.h` are actually correct for your platform!
+
+### stdarg.h
+
+In most cases, the correct version of stdarg.h is the version provided
+with your toolchain.  However, sometimes there are issues with
+using your toolchains `stdarg.h`.  For example, it may attempt to draw in
+header files that do not exist in NuttX or perhaps the header files that
+it uses are not compatible with the NuttX header files.  In those cases,
+you can use an architecture-specific `stdarg.h` header file by defining
+`CONFIG_ARCH_STDARG_H=y`.
+
+See the discussion above for the `math.h` header.  This setting works
+exactly the same for the `stdarg.h` header file.
+
+# CONFIGURING NUTTX
+
+## Instantiating "Canned" Configurations
+
+### `configure.sh` and `configure.bat`
+
+"Canned" NuttX configuration files are retained in:
+
+    boards/<arch-name>/<chip-name>/<board-name>/configs/<config-dir>
+
+Where `<board-name>` is the name of your development board and `<config-dir>`
+is the name of the sub-directory containing a specific configuration for
+that board. `<arch-name>` and `<chip-name>` refer to characteristics of the
+MCU used on the board: `<arch-name>` is the CPU architecture implemented
+by the MCU; `<chip-name>` identifies the MCU chip family.  Only a few
+steps are required to instantiate a NuttX configuration, but to make the
+configuration even easier there are scripts available in the tools/
+sub-directory combines those simple steps into one command.
+
+There is one tool for use with any Bash-like shell that does configuration
+steps.  It is used as follows:
+
+    tools/configure.sh <board-name>:<config-dir>
+
+There is an alternative Windows batch file that can be used in the windows
+native environment like:
+
+    tools\configure.bat <board-name>:<config-dir>
+
+And, to make sure that other platforms are supported, there is also a
+C program at tools/configure.c that can be compiled to establish the
+board configuration.
+
+See `tools/README.txt` for more information about these scripts.
+
+General information about configuring NuttX can be found in:
+
+    {TOPDIR}/boards/README.txt
+    {TOPDIR}/boards/<arch-name>/<chip-name>/<board-name>/README.txt
+
+### The Hidden Configuration Scripts:
+
+As mentioned above, there are only a few simple steps to instantiating a
+NuttX configuration.  Those steps are hidden by the configuration scripts
+but are summarized below:
+  
+  1. Copy Files
+  
+     Configuring NuttX requires only copying two files from the
+     `<config-dir>` to the directory where you installed NuttX (TOPDIR):
+  
+       * Copy `boards/<arch-name>/<chip-name>/<board-name>/configs/<config-dir>/Make.def` to `{TOPDIR}/Make.defs`
+    
+         OR
+    
+       * Copy `boards/<arch-name>/<chip-name>/<board-name>/scripts/Make.def`
+         to `{TOPDIR}/Make.defs`
+    
+         Make.defs describes the rules needed by your tool chain to compile
+         and link code.  You may need to modify this file to match the
+         specific needs of your toolchain.  NOTE that a configuration may
+         have its own unique Make.defs file in its configuration directory or
+         it may use a common Make.defs file for the board in the scripts/
+         directory.  The first takes precedence.
+    
+       * Copy `boards/<arch-name>/<chip-name>/<board-name>/configs/<config-dir>/defconfig` to `{TOPDIR}/.config`
+    
+         The defconfig file holds the actual build configuration.  This
+         file is included by all other make files to determine what is
+         included in the build and what is not.  This file is also used
+         to generate a C configuration header at `include/nuttx/config.h`.
+    
+       * Copy other, environment-specific files to `{TOPDIR}`
+    
+         This might include files like .gdbinit or IDE configuration files
+         like .project or .cproject.
+  
+  2. Refresh the Configuration
+  
+     New configuration setting may be added or removed.  Existing settings
+     may also change there values or options.  This must be handled by
+     refreshing the configuration as described below.
+    
+     NOTE:  NuttX uses only compressed defconfig files.  For the NuttX
+     defconfig files, this refreshing step is *NOT* optional; it is also
+     necessary to uncompress and regenerate the full making file.  This is
+     discussed further below.
+
+## Refreshing Configurations
+
+Configurations can get out of date.  As new configuration settings are
+added or removed or as dependencies between configuration settings
+change, the contents of a default configuration can become out of synch
+with the build systems.  Hence, it is a good practice to "refresh" each
+configuration after configuring and before making.  To refresh the
+configuration, use the NuttX Configuration Tool like this:
+
+    make oldconfig
+
+AFTER you have instantiated the NuttX configuration as described above.
+The configuration step copied the .config file into place in the top-level
+NuttX directory; 'make oldconfig' step will then operate on that .config
+file to bring it up-to-date.
+
+If your configuration is out of date, you will be prompted by 'make oldconfig'
+to resolve the issues detected by the configuration tool, that is, to
+provide values for the new configuration options in the build system.  Doing
+this can save you a lot of problems down the road due to obsolete settings in
+the default board configuration file.  The NuttX configuration tool is
+discussed in more detail in the following paragraph.
+
+Confused about what the correct value for a new configuration item should
+be?  Enter ? in response to the 'make oldconfig' prompt and it will show
+you the help text that goes with the option.
+
+If you don't want to make any decisions are willing to just accept the
+recommended default value for each new configuration item, an even easier
+way is:
+
+    make olddefconfig
+
+The olddefconfig target will simply bring your configuration up to date with
+the current Kconfig files, setting any new options to the default value.
+No questions asked.
+
+## NuttX Configuration Tool
+
+An automated tool has been incorporated to support re-configuration
+of NuttX.  This tool is based on the kconfig-frontends application available
+at <https://bitbucket.org/nuttx/tools/src/master/kconfig-frontends/>.  (This
+is a snapshot of the old <http://ymorin.is-a-geek.org/projects/kconfig-frontends>
+which is no longer available.)  This application provides a tool called
+`kconfig-mconf` that is used by the NuttX top-level Makefile. The following
+make target is provided:
+
+    make menuconfig
+
+This make target will bring up NuttX configuration menus.
+
+**WARNING**:  Never do `make menuconfig` on a configuration that has
+not been converted to use the kconfig-frontends tools!  This will
+damage your configuration (see
+<http://www.nuttx.org/doku.php?id=wiki:howtos:convertconfig>).
+
+How do we tell a new configuration from an old one? See "Incompatibilities
+with Older Configurations" below.
+
+The `menuconfig` make target depends on two things:
+
+  1. The Kconfig configuration data files that appear in almost all
+     NuttX directories.  These data files are the part that is still
+     under development (patches are welcome!).  The Kconfig files
+     contain configuration information for the configuration settings
+     relevant to the directory in which the Kconfig file resides.
+     
+     NOTE: For a description of the syntax of this configuration file,
+     see kconfig-language.txt in the tools repository at
+     <https://bitbucket.org/nuttx/tools>
+  
+  2. The `kconfig-mconf` tool. `kconfig-mconf` is part of the
+     kconfig-frontends package.  You can download that package from the
+     snapshot in the tools repository at <https://bitbucket.org/nuttx/tools>.
+  
+     Building kconfig-frontends under Linux may be as simple as
+     `configure; make; make install` but there may be some build
+     complexities, especially if you are building under Cygwin.  See
+     the more detailed build instructions in the top-level README.txt
+     file of the tools repository at <https://bitbucket.org/nuttx/tools>.
+  
+  
+     The `make install` step will, by default, install the `kconfig-mconf`
+     tool at `/usr/local/bin/mconf`.  Where ever you choose to
+     install `kconfig-mconf`, make certain that your PATH variable includes
+     a path to that installation directory.
+  
+     The kconfig-frontends tools will not build in a native Windows
+     environment directly "out-of-the-box".  For the Windows native
+     case, you can use the modified version of kconfig-frontends
+     that can be found at
+
+     <http://uvc.de/posts/linux-kernel-configuration-tool-kconfig-under-windows.html>  
+
+     or a more recent port that can be found at  
+
+     <http://reclonelabs.com/more-kconfig-awesomeness-for-windows/>.
+   
+The basic configuration order is "bottom-up":
+   
+   - Select the build environment,
+   - Select the processor,
+   - Select the board,
+   - Select the supported peripherals
+   - Configure the device drivers,
+   - Configure the application options on top of this.
+   
+This is pretty straight forward for creating new configurations
+but may be less intuitive for modifying existing configurations.
+
+Another ncurses-based tool that is an option to kconfig-mconf is
+kconfig-nconf.  The differences are primary in in the aesthetics of the
+UI.  If you have kconfig-nconf built, then you can invoke that front end
+with:
+   
+     make nconfig
+   
+If you have an environment that supports the Qt or GTK graphical systems
+(probably KDE or gnome, respectively, or Cygwin under Windows with Qt or
+GTK installed), then you can also build the graphical kconfig-frontends,
+kconfig-qconf and kconfig-gconf.  In these case, you can start the
+graphical configurator with either:
+   
+     make qconfig
+   
+ or
+   
+     make gconfig
+   
+Some keyboard shortcuts supported by kconfig-mconf, the tool that runs
+when you do 'make menuconfig':
+
+   - `?` will bring up the mconfig help display.
+   
+   - `/` can be used find configuration selections.
+   
+   - `Z` can be used to reveal hidden configuration options
+   
+These last two shortcuts are described further in the following
+paragraphs.
+
+## Finding Selections in the Configuration Menus
+
+The NuttX configuration options have gotten complex and it can be very
+difficult to find options in the menu trees if you are not sure where
+to look.  The "basic configuration order" describe above can help to
+narrow things down.
+
+But if you know exactly what configuration setting you want to select,
+say CONFIG_XYZ, but not where to find it, then the 'make menuconfig'
+version of the tool offers some help:  By pressing the '/' key, the
+tool will bring up a menu that will allow you to search for a
+configuration item.  Just enter the string CONFIG_XYZ and press 'ENTER'.
+It will show you not only where to find the configuration item, but
+also all of the dependencies related to the configuration item.
+
+## Reveal Hidden Configuration Options
+
+If you type `Z`, then kconfig-mconf will change what is displayed.
+Normally, only enabled features that have all of their dependencies met
+are displayed.  That is, of course, not very useful if you would like to
+discover new options or if you are looking for an option and do not
+realize that the dependencies have not yet been selected and, hence, it
+is not displayed.
+
+But if you enter `Z`, then every option will be shown, whether or not its
+dependencies have been met.  You can then see everything that could be
+selected with the right dependency selections.  These additional options
+will be shown the `-` for the selection and for the value (since it
+cannot be selected and has no value).  About all you do is to select
+the `<Help>` option to see what the dependencies are.
+
+## Make Sure that You are on the Right Platform
+
+Saved configurations may run on Linux, Cygwin (32- or 64-bit), or other
+platforms.  The platform characteristics can be changed use `make
+menuconfig`.  Sometimes this can be confusing due to the differences
+between the platforms.  Enter sethost.sh
+
+sethost.sh is a simple script that changes a configuration to your
+host platform.  This can greatly simplify life if you use many different
+configurations.  For example, if you are running on Linux and you
+configure like this:
+
+    tools/configure.sh board:configuration
+
+The you can use the following command to both (1) make sure that the
+configuration is up to date, AND (2) the configuration is set up
+correctly for Linux:
+
+    tools/sethost.sh -l
+
+Or, if you are on a Windows/Cygwin 64-bit platform:
+
+    tools/sethost.sh -c
+
+Or, for MSYS/MSYS2:
+
+    tools/sethost.sh -g
+
+Other options are available from the help option built into the
+script.  You can see all options with:
+
+    tools/sethost.sh -h
+
+Recently, the options to the configure.sh (and configure.bat) scripts have
+been extended so that you both setup the configuration, select for the host
+platform that you use, and uncompress and refresh the defconfig file all in
+one command like:
+
+    tools/configure.sh -l board:configuration
+
+For a Linux host or for a Windows/Cygwin host:
+
+    tools/configure.sh -c board:configuration
+
+Other options are available from the help option built into the
+script.  You can see all options with:
+
+    tools/configure.sh -h
+
+## Comparing Two Configurations
+
+If you try to compare two configurations using 'diff', you will probably
+not be happy with the result.  There are superfluous things added to
+the configuration files that make comparisons with the human eye
+difficult.
+
+There is a tool at nuttx/tools/cmpconfig.c that can be built to simplify
+these comparisons.  The output from this difference tool will show only
+the meaningful differences between two configuration files.  This tool is
+built as follows:
+
+    cd nuttx/tools
+    make -f Makefile.host
+
+This will create a program called 'cmpconfig' or 'comconfig.exe' on Windows.
+
+Why would you want to compare two configuration files?  Here are a few
+of the reasons why I do this
+
+  1. When I create a new configuration I usually base it on an older
+     configuration and I want to know, "What are the options that I need to
+     change to add the new feature to the older configurations?"  For example,
+     suppose that I have a boardA/nsh configuration and I want to create a
+     boardA/nxwm configuration.  Suppose I already have boardB/nsh and
+     boardB/nxwm configurations.  Then by comparing the boardB/nsh with the
+     boardB/nxwm I can see the modifications that I would need to make to my
+     boardA/nsh to create a new  boardA/nxwm.
+  
+  2. But the most common reason that I use the 'cmpconfig' program is to
+     check the results of "refreshing" a configuration with 'make oldconfig'
+     (see the paragraph "Refreshing Configurations" above).  The 'make
+     oldconfig' command will make changes to my configuration and using
+     'cmpconfig', I can see precisely what those changes were and if any
+     should be of concern to me.
+  
+  3. The 'cmpconfig' tool can also be useful when converting older, legacy
+     manual configurations to the current configurations based on the
+     kconfig-frontends tools.  See the following paragraph.
+
+## Making defconfig Files
+
+### .config Files as defconfig Files:
+
+The minimum defconfig file is simply the generated .config file with
+CONFIG_APPS_DIR setting removed or commented out.  That setting provides
+the name and location of the apps/ directory relative to the nuttx build
+directory.  The default is ../apps/, however, the apps directory may be
+any other location and may have a different name.  For example, the name
+of versioned NuttX releases are always in the form apps-xx.yy where xx.yy
+is the version number.
+
+### Finding the apps/ Directory Path:
+
+When the default configuration is installed using one of the scripts or
+programs in the NuttX tools directory, there will be an option to provide
+the path to the apps/ directory.  If not provided, then the configure tool
+will look around and try to make a reasonable decision about where the
+apps/ directory is located.
+
+### Compressed defconfig Files:
+
+The Makefile also supports an option to generate very small defconfig
+files.  The .config files are quite large and complex.  But most of the
+settings in the .config file simply have the default settings from the
+Kconfig files.  These .config files can be converted into small defconfig
+file:
+    
+    make savedefconfig
+    
+That make target will generate a defconfig file in the top-level
+directory.  The size reduction is really quite remarkable:
+    
+    wc -l .config defconfig
+     1085 .config
+       82 defconfig
+     1167 total
+    
+In order to be usable, the .config file installed from the compressed
+defconfig file must be reconstituted using:
+    
+    make olddefconfig
+    
+  > **NOTE 1**:  Only compressed defconfig files are retained in the NuttX repository.
+  > All patches and PRs that attempt to add or modify a defconfig file MUST
+  > use the compressed defconfig format as created by 'make savdefconfig.'
+    
+  > **NOTE 2**:  When 'make savedefconfig' runs it will try several things some of
+  > which are expected to fail.  In these cases you will see an error message
+  > from make followed by "(ignored)."  You should also ignore these messages
+    
+**CAUTION**:  This size reduction was accomplished by removing all setting
+from the .config file that were at the default value.  'make olddefconfig'
+can regenerate the original .config file by simply restoring those default
+settings.  The underlying assumption here is, of course, that the default
+settings do not change.  If the default settings change, and they often
+do, then the original .config may not be reproducible.
+
+So if your project requires 100% reproducibility over a long period of
+time, you make want to save the complete .config files vs. the standard,
+compressed defconfig file.
+
+### Configuring with "Compressed" defconfig Files:
+
+As described above defconfig, all NuttX defconfig files are compressed
+using 'make savedeconfig'.  These compressed defconfig files are
+generally not fully usable as they are and may not build the target
+binaries that you want because the compression process removed all of
+the default settings from the defconfig file.  To restore the default
+settings, you should run the following after configuring:
+
+    make olddefconfig
+
+That will restore the the missing defaulted values.
+
+Using this command after configuring is generally a good practice anyway:
+Even if the defconfig files are not "compressed" in this fashion, the
+defconfig file may be old and the only way to assure that the installed
+.config is is up to date is via 'make oldconfig' or 'make olddefconfig'.
+See the paragraph above entitled ""Refreshing Configurations" for
+additional information.
+
+## Incompatibilities with Older Configurations
+
+**WARNING**
+
+The current NuttX build system supports *only* the new compressed,
+defconfig configuration files generated using the kconfig-frontends tools
+as described in the preceding section.  Support for the older, legacy,
+manual configurations was eliminated in NuttX 7.0; support for
+uncompressed .config-files-as-defconfig files was eliminated after
+NuttX-7.21.  All configurations must now be done using the
+kconfig-frontends tool.  The older manual configurations and the new
+kconfig-frontends configurations are not compatible.  Old legacy
+configurations can *not* be used with the kconfig-frontends tool and,
+hence, cannot be used with releases of NuttX 7.0 and beyond:
+
+If you run 'make menuconfig' with a legacy configuration the resulting
+configuration will probably not be functional.
+
+  > Q: How can I tell if a configuration is a new kconfig-frontends
+  >   configuration or an older, manual configuration?
+  >
+  > A: Only old, manual configurations will have an appconfig file
+  > 
+  > Q: How can I convert a older, manual configuration into a new,
+  >    kconfig-frontends toolchain.
+  >
+  > A: Refer to <http://www.nuttx.org/doku.php?id=wiki:howtos:convertconfig>
+  
+**WARNING**
+
+As described above, whenever you use a configuration, you really should
+always refresh the configuration with the following command *before* you
+make NuttX:
+
+    make oldconfig
+
+OR
+
+    make olddefconfig
+
+This will make sure that the configuration is up-to-date in the event that
+it has lapsed behind the current NuttX development (see the paragraph
+"Refreshing Configurations" above).  But this only works with *new*
+configuration files created with the kconfig-frontends tools.
+
+Further, this step is *NOT* optional with the new, compressed defconfig
+files.  It is a necessary step that will also uncompress the defconfig
+file, regenerating the .config and making it usable for NuttX builds.
+
+Never do `make oldconfig` (OR `make menuconfig`) on a  configuration that
+has not been converted to use the kconfig-frontends tools!  This will
+damage your configuration (see
+<http://www.nuttx.org/doku.php?id=wiki:howtos:convertconfig>).
+
+## NuttX Configuration Tool under DOS
+
+  Recent versions of NuttX support building NuttX from a native Windows
+  console window (see *Native Windows Build* below).  But kconfig-frontends
+  is a Linux tool.  At one time this was a problem for Windows users, but
+  now there are two specially modified versions of the kconfig-frontends
+  tools that can be used.  One can be found here:
+  <http://uvc.de/posts/linux-kernel-configuration-tool-kconfig-under-windows.html>
+
+  The configuration steps of the most recent versions of NuttX require the
+  kconfig-tweak tool that is not not available in the the above.  However,
+  there has been an update to this Kconfig Windows tools that does include
+  kconfig-tweak:  http://reclonelabs.com/more-kconfig-awesomeness-for-windows/
+
+  Source code is available here: <https://github.com/reclone/kconfig-frontends-win32>
+  and <https://github.com/reclone/kconfig-frontends-win32/releases>
+
+  It is also possible to use the version of kconfig-frontends built
+  under Cygwin outside of the Cygwin "sandbox" in a native Windows
+  environment:
+
+  1. You can run the configuration tool using Cygwin.  However, the
+     Cygwin Makefile.win will complain so to do this will, you have
+     to manually edit the .config file:
+     
+     a. Delete the line: CONFIG_WINDOWS_NATIVE=y
+     
+     b. Change the apps/ directory path, CONFIG_APPS_DIR to use Unix
+      
+        style delimiters.  For example, change "..\apps" to "../apps"
+     
+     And of course, after you use the configuration tool you need to
+     restore CONFIG_WINDOWS_NATIVE=y and the correct CONFIG_APPS_DIR.
+
+  2. You can, with some effort, run the Cygwin kconfig-mconf tool
+     directly in the Windows console window.  In this case, you do not
+     have to modify the .config file, but there are other complexities:
+     
+    a. You need to temporarily set the Cygwin directories in the PATH
+       variable then run kconfig-mconf manually like:
+         
+          kconfig-mconf Kconfig
+         
+       There is a Windows batch file at tools/kconfig.bat that automates
+       these steps:
+         
+         tools/kconfig menuconfig
+     
+    b. There is an issue with accessing DOS environment variables from
+       the Cygwin kconfig-mconf running in the Windows console.  The
+       following change to the top-level Kconfig file seems to work
+       around these problems:
+     
+          config APPSDIR
+              string
+          -   option env="APPSDIR"
+          +   default "../apps"
+
+# TOOLCHAINS
+
+## Cross-Development Toolchains
+
+  In order to build NuttX for your board, you will have to obtain a cross-
+  compiler to generate code for your target CPU.  For each board,
+  configuration, there is a README.txt file (at
+  `boards/<arch-name>/<chip-name>/<board-name>/README.txt`).
+  That README file contains suggestions and information about appropriate
+  tools and development environments for use with your board.
+
+  In any case, the PATH environment variable will need to be updated to
+  include the location where the build can find the toolchain binaries.
+
+## NuttX Buildroot Toolchain
+
+  For many configurations, a DIY set of tools is available for NuttX.  These
+  tools can be downloaded from the NuttX Bitbucket.org file repository.  After
+  unpacking the buildroot tarball, you can find instructions for building
+  the tools in the `buildroot/boards/README.txt` file.
+
+  Check the README.txt file in the configuration directory for your board
+  to see if you can use the buildroot toolchain with your board (this
+  README.txt file is located in
+  `boards/<arch-name>/<chip-name>/<board-name>/README.txt`).
+
+  This toolchain is available for both the Linux and Cygwin development
+  environments.
+
+  Advantages:  (1) NuttX header files are built into the tool chain,
+  and (2) related support tools like NXFLAT tools, the ROMFS
+  genromfs tools, and the kconfig-frontends tools can be built into your
+  toolchain.
+
+  Disadvantages:  This tool chain is not was well supported as some other
+  toolchains.  GNU tools are not my priority and so the buildroot tools
+  often get behind.  For example, until recently there was no EABI support
+  in the NuttX buildroot toolchain for ARM.
+
+  NOTE: For Cortex-M3/4, there are OABI and EABI versions of the buildroot
+  toolchains.  If you are using the older OABI toolchain the prefix for
+  the tools will be arm-nuttx-elf-; for the EABI toolchain the prefix will
+  be arm-nuttx-eabi-.  If you are using the older OABI toolchain with
+  an ARM Cortex-M3/4, you will need to set CONFIG_ARMV7M_OABI_TOOLCHAIN
+  in the .config file in order to pick the right tool prefix.
+
+  If the make system ever picks the wrong prefix for your toolchain, you
+  can always specify the prefix on the command to override the default
+  like:
+
+    make CROSSDEV=arm-nuttx-elf
+
+# SHELLS
+
+The NuttX build relies on some shell scripts.  Some are inline in the
+Makefiles and many are executable scripts in the tools/. directory.  The
+scripts were all developed using bash and many contain bash shell
+dependencies.
+
+Most of the scripts begin with #!/bin/bash to specifically select the
+bash shell.  Some still have #!/bin/sh but I haven't heard any complaints
+so these must not have bash dependencies.
+
+There are two shell issues that I have heard of:
+
+  1. Linux where /bin/sh refers to an incompatible shell (like ksh or csh).
+     
+     In this case, bash is probably available and the #!/bin/bash at the
+     beginning of the file should do the job.  If any scripts with #!/bin/sh
+     fail, try changing that to #!/bin/bash and let me know about the change.
+  
+  2. FreeBSD with the Bourne Shell and no bash shell.
+     
+     The other, reverse case has also been reported on FreeBSD setups that
+     have the Bourne shell, but not bash.  In this base, `#!/bin/bash` fails
+     but `#!/bin/sh` works okay.  My recommendation in this case is to create
+     a symbolic link at `/bin/bash` that refers to the Bourne shell.
+     
+     There may still be issues, however, with certain the bash-centric scripts
+     that will require modifications.
+  
+# BUILDING NUTTX
+
+## Building
+
+NuttX builds in-place in the source tree.  You do not need to create
+any special build directories.  Assuming that your Make.defs is setup
+properly for your tool chain and that PATH environment variable contains
+the path to where your cross-development tools are installed, the
+following steps are all that are required to build NuttX:
+
+    cd {TOPDIR}
+    make
+
+At least one configuration (eagle100) requires additional command line
+arguments on the make command.  Read
+`{TOPDIR}/boards/<arch-name>/<chip-name>/<board-name>/README.txt` to see
+if that applies to your target.
+
+## Re-building
+
+Re-building is normally simple -- just type make again.
+
+But there are some things that can "get you" when you use the Cygwin
+development environment with Windows native tools.  The native Windows
+tools do not understand Cygwin's symbolic links, so the NuttX make system
+does something weird:  It copies the configuration directories instead of
+linking to them (it could, perhaps, use the NTFS 'mklink' command, but it
+doesn't).
+
+A consequence of this is that you can easily get confused when you edit
+a file in one of the linked (i.e., copied) directories, re-build NuttX,
+and then not see your changes when you run the program.  That is because
+build is still using the version of the file in the copied directory, not
+your modified file!
+
+Older versions of NuttX did not support dependencies in this
+configuration.  So a simple work around this annoying behavior in this
+case was the following when you re-build:
+
+     make clean_context all
+
+This 'make' command will remove of the copied directories, re-copy them,
+then make NuttX.
+
+However, more recent versions of NuttX do support dependencies for the
+Cygwin build.  As a result, the above command will cause everything to be
+rebuilt (because it removes and will cause recreating the
+include/nuttx/config.h header file).  A much less gracefully but still
+effective command in this case is the following for the ARM configuration:
+
+    rm -rf arch/arm/src/chip arch/arm/src/board
+
+This "kludge" simple removes the copied directories.  These directories
+will be re-created when you do a normal 'make' and your edits will then be
+effective.
+
+## Build Targets and Options
+
+### Build Targets
+
+Below is a summary of the build targets available in the top-level
+NuttX Makefile:
+
+  * `all`
+
+    The default target builds the NuttX executable in the selected output
+    formats.
+
+  * `clean`
+
+    Removes derived object files, archives, executables, and temporary
+    files, but retains the configuration and context files and directories.
+
+  * `distclean`
+
+    Does 'clean' then also removes all configuration and context files.
+    This essentially restores the directory structure to its original,
+    unconfigured stated.
+
+Application housekeeping targets.  The APPDIR variable refers to the user
+application directory.  A sample apps/ directory is included with NuttX,
+however, this is not treated as part of NuttX and may be replaced with a
+different application directory.  For the most part, the application
+directory is treated like any other build directory in the Makefile script.
+However, as a convenience, the following targets are included to support
+housekeeping functions in the user application directory from the NuttX
+build directory.
+
+  * `apps_clean`
+
+    Perform the clean operation only in the user application directory
+
+  * `apps_distclean`
+
+    Perform the distclean operation only in the user application directory.
+    The apps/.config file is preserved so that this is not a "full" distclean
+    but more of a configuration "reset" for the application directory.
+
+  * `export`
+
+    The export target will package the NuttX libraries and header files into
+    an exportable package.  Caveats: (1) These needs some extension for the KERNEL
+    build. (2) The logic in tools/mkexport.sh only supports GCC and, for example,
+    explicitly assumes that the archiver is 'ar'
+
+  * `download`
+
+    This is a helper target that will rebuild NuttX and download it to the target
+    system in one step.  The operation of this target depends completely upon
+    implementation of the DOWNLOAD command in the user Make.defs file.  It will
+    generate an error an error if the DOWNLOAD command is not defined.
+
+The following targets are used internally by the make logic but can be invoked
+from the command under certain conditions if necessary.
+
+  * `depend`
+
+    Create build dependencies. (NOTE:  There is currently no support for build
+    dependencies under Cygwin using Windows-native toolchains.)
+
+  * `context`
+
+    The context target is invoked on each target build to assure that NuttX is
+    properly configured.  The basic configuration steps include creation of the
+    the config.h and version.h header files in the include/nuttx directory and
+    the establishment of symbolic links to configured directories.
+
+  * `clean_context`
+
+    This is part of the distclean target.  It removes all of the header files
+    and symbolic links created by the context target.
+
+### Build Options
+
+Of course, the value any make variable an be overridden from the make command
+line.  However, there is one particular variable assignment option that may
+be useful to you:
+
+  * `V=1`
+
+    This is the build "verbosity flag."  If you specify V=1 on the make command
+    line, you will see the exact commands used in the build. This can be very
+    useful when adding new boards or tracking down compile time errors and
+    warnings (Contributed by Richard Cochran).
+
+## Native Windows Build
+
+The beginnings of a Windows native build are in place but still not often
+used as of this writing.  The build was functional but because of lack of
+use may find some issues to be resolved with this build configuration.
+
+The windows native build logic initiated if CONFIG_WINDOWS_NATIVE=y is

Review comment:
       ```suggestion
   The windows native build logic initiated if `CONFIG_WINDOWS_NATIVE=y` is
   ```

##########
File path: README.md
##########
@@ -0,0 +1,2513 @@
+# APACHE NUTTX (INCUBATING)
+
+* Introduction
+  - Incubation Status
+* Community
+  - Getting Help
+  - Mailing Lists
+  - Issue Tracker
+  - Source Code
+  - Website Source Code
+* Environments
+  - Installing Cygwin
+  - Ubuntu Bash under Windows 10
+  - Using macOS
+* Installation
+  - Download and Unpack
+  - Semi-Optional apps/ Package
+  - Installation Directories with Spaces in the Path
+  - Downloading from Repositories
+  - Related Repositories
+  - Notes about Header Files
+* Configuring NuttX
+  - Instantiating "Canned" Configurations
+  - Refreshing Configurations
+  - NuttX Configuration Tool
+  - Finding Selections in the Configuration Menus
+  - Reveal Hidden Configuration Options
+  - Make Sure that You are on the Right Platform
+  - Comparing Two Configurations
+  - Making defconfig Files
+  - Incompatibilities with Older Configurations
+  - NuttX Configuration Tool under DOS
+* Toolchains
+  - Cross-Development Toolchains
+  - NuttX Buildroot Toolchain
+* Shells
+* Building NuttX
+  - Building
+  - Re-building
+  - Build Targets and Options
+  - Native Windows Build
+  - Installing GNUWin32
+* Cygwin Build Problems
+  - Strange Path Problems
+  - Window Native Toolchain Issues
+* Documentation
+
+# INTRODUCTION
+
+Apache NuttX (Incubating) is a real-time operating system (RTOS) with an
+emphasis on standards compliance and small footprint.  Scalable from 8-bit
+to 32-bit microcontroller environments, the primary governing standards in
+NuttX are POSIX and ANSI standards. Additional standard APIs from Unix and
+other common RTOSs (such as VxWorks) are adopted for functionality not
+available under these standards, or for functionality that is not
+appropriate for deeply-embedded environments (such as fork()).
+
+Extensive documentation can be found on the project wiki:
+  <https://cwiki.apache.org/NUTTX/Nuttx>
+
+## Incubation Status
+
+Apache NuttX (Incubating) is an effort undergoing Incubation at The Apache
+Software Foundation (ASF), sponsored by the Incubator.  For more on our
+incubation effort, please see the file DISCLAIMER-WIP, in the same
+directory as this README.
+
+For brevity, the rest of this file will refer to it as Apache NuttX or
+simply NuttX.
+
+# COMMUNITY
+
+Every volunteer project obtains its strength from the people involved in
+it.  We invite you to participate as much or as little as you choose.
+
+We encourage you to:
+
+  - Use our project and provide feedback.
+  - Provide us with use-cases.
+  - Report bugs and submit patches.
+  - Contribute code or documentation.
+
+## Getting Help
+
+The best place to get help is the developer's mailing list.  Please see
+the following section:
+
+## Mailing Lists
+
+Get help using NuttX or contribute to the project on our mailing lists:
+
+  * <de...@nuttx.apache.org> is for people who want to contribute code to NuttX.
+    * To subscribe, send an email to <de...@nuttx.apache.org>.
+    * To unsubscribe, send an email to <de...@nuttx.apache.org>.
+    * View the archives at:
+      <https://www.mail-archive.com/dev@nuttx.apache.org/>
+
+  * <co...@nuttx.apache.org> is a read-only list that notifies subscribers
+  about commit messages and patches to NuttX.
+    * To subscribe, send an email to <co...@nuttx.apache.org>.
+    * To unsubscribe, send an email to <co...@nuttx.apache.org>.
+    * View the archives at:
+      <https://www.mail-archive.com/commits@nuttx.apache.org/>
+
+## Issue Tracker
+
+### Bug Reports:
+
+Found bug? Send an email to the dev list: <de...@nuttx.apache.org>
+
+Before submitting an issue, please:
+
+  - Verify that the bug does in fact exist. 
+  
+  - Search the mailing list archives to verify there is no existing issue
+    reporting the bug you've found.
+ 
+  - Consider tracking down the bug yourself in the NuttX source code and
+    submitting a patch along with your bug report.  This is a great time
+    saver for the NuttX developers and helps ensure the bug will be fixed
+    quickly.
+  
+### Feature Requests:
+  
+Enhancement requests for new features are also welcome. The more concrete
+and rational the request is, the greater the chance it will incorporated
+into future releases.
+
+## Source Code
+
+The project sources are in two Git repositories.  The core OS is in
+incubator-nuttx and the apps repository is in incubator-nuttx-apps.  These
+are housed in GitBox on ASF servers and also mirrored at GitHub.  These
+are kept in sync, so you can use whichever option you prefer.
+
+  - NuttX core OS repository:
+    
+    - Primary:
+      <https://gitbox.apache.org/repos/asf?p=incubator-nuttx.git>
+    
+    - GitHub Mirror:
+      <https://github.com/apache/incubator-nuttx>
+  
+  - Apps repository:
+    
+    - Primary:
+      <https://gitbox.apache.org/repos/asf?p=incubator-nuttx-apps.git>
+    
+    - GitHub Mirror:
+      <https://github.com/apache/incubator-nuttx-apps>
+
+## Website Source Code
+
+The project website sources are accessible via the website source code
+  repository which is also mirrored in GitHub:
+
+- Primary:
+  <https://gitbox.apache.org/repos/asf?p=incubator-nuttx-website.git>
+
+- GitHub Mirror:
+  <https://github.com/apache/incubator-nuttx-website>
+
+# ENVIRONMENTS
+
+  NuttX requires a POSIX development environment such as you would find under
+  Linux or macOS.  NuttX may also be installed and built on Windows system
+  if you also provide such a POSIX development environment.  Options for a
+  POSIX development environment under Windows include:
+
+  - An installation of Linux on a virtual machine (VM) in Windows.  I have
+    not been happy using a VM myself.  I have had stability problems with
+    open source VMs and commercial VMs cost more than I want to spend.
+    Sharing files with Linux running in a VM is awkward;  sharing devices
+    connected to the Windows box with Linux in a VM is, at the very least,
+    confusing;  Using Windows tools (such as Segger J-Link) with files
+    built under the Linux VM is not a possibility.
+
+  - The Cygwin environment.  Instructions for installation of Cygwin on a
+    Windows system are provided in the following paragraph, "Installing
+    Cygwin".  Cygwin is a mature, well-tested, and very convenient
+    environment.  It is especially convenient if you  need to
+    integrate with Windows tools and files.  Downsides are that the
+    installation time is very long and the compile times are slow.
+
+  - Ubuntu/Bash shell under Windows 10.  This is a new option under
+    Windows 10.  See the section "Ubuntu Bash under Windows 10" below.
+    This is an improvement over Cygwin if your concern is compile time;
+    its build performance is comparable to native Linux, certainly better
+    than the Cygwin build time.  It also installs in a tiny fraction of
+    the time as Cygwin, perhaps 20 minutes for the basic Ubuntu install
+    (vs. more than a day for the complete Cygwin install).
+  
+    There have been even more recent ports of Linux environment to
+    Windows.  I need to update this section to include some mention of
+    these alternatives.
+
+  - The MSYS environment.  MSYS derives from an older version of Cygwin
+    simplified and adapted to work more naturally in the Windows
+    environment.  See <http://www.mingw.org/wiki/MSYS> if you are
+    interested in using MSYS.  The advantages of the MSYS environment is
+    that it is better integrted with the native Windows environment and
+    lighter weight; it uses only a  minimal number of add-on POSIX-land
+    tools.
+  
+    The download link in that Wiki takes you to the SourceForge download
+    site.  The SourceForge MSYS project has been stagnant for some time.
+    The MSYS project has more recently moved to
+    <http://odsn.net/projects/sfnet_mingwbundle>.  Downloads of current .zip
+    files are available there but no instructions for the installation.
+
+  - MSYS2 appears to be a re-write of MSYS based on a newer version of
+    Cygwin.  Is it available at <https://www.msys2.org>.  A windows
+    installer is available at that site along with very good installation
+    instructions.  The download is relatively quick (at least compared to
+    Cygwin) and the 'pacman' package management tool supports supports
+    simple system updates.  For example, 'pacman -S git' will install the
+    GIT command line utilities.
+
+  - Other POSIX environments.  Check out:
+    
+    - UnxUtils: <https://sourceforge.net/projects/unxutils/>,
+      <https://en.wikipedia.org/wiki/UnxUtils>
+    - MobaXterm: <https://mobaxterm.mobatek.net/>
+    - Gow: <https://github.com/bmatzelle/gow/wiki>
+  
+    **Disclaimer**:  In principle, these should work.  However, I have never
+    used any of these environments and cannot guarantee that there is
+    not some less-than-obvious issues.
+  
+NuttX can also be installed and built on a native Windows system, but with
+some potential tool-related issues (see the discussion "Native Windows
+Build" under "Building NuttX" below).  GNUWin32 is used to provide
+compatible native windows tools.
+
+## Installing Cygwin
+
+Installing Cygwin on your Windows PC is simple, but time consuming.  See
+<http://www.cygwin.com/> for installation instructions. Basically you just
+need to download a tiny setup.exe program and it does the real, network
+installation for you.
+
+Some Cygwin installation tips:
+
+  1. Install at `C:\cygwin`
+  
+  2. Install **everything**:  "Only the minimal base packages from the
+     Cygwin distribution are installed by default. Clicking on categories
+     and packages in the setup.exe package installation screen will
+     provide you with the ability to control what is installed or updated.
+     Clicking on the "Default" field next to the "All" category will
+     provide you with the opportunity to install every Cygwin package.
+     Be advised that this will download and install hundreds of megabytes
+     to your computer."
+   
+If you use the "default" installation, you will be missing many
+of the Cygwin utilities that you will need to build NuttX.  The
+build will fail in numerous places because of missing packages.
+
+NOTE: The last time I installed **everything**, the download was
+about 5GiB.  The server I selected was also very slow so it took
+over a day to do the whole install!
+
+NOTE: You don't really have to install **everything** but I cannot
+answer the question "Then what should I install?"  I don't know
+the answer to that and so will continue to recommend installing
+**everything**.
+
+You should certainly be able to omit "Science", "Math", and
+"Publishing".  You can try omitting KDE, Gnome, GTK, and other
+graphics packages if you don't plan to use them.
+
+Perhaps a minimum set would be those packages listed below for the
+"Ubuntu Bash under Windows 10" installation?
+
+**UPDATE**:  Sergey Frolov had success with the following minimal
+Cygwin configuration:
+   
+   1. After starting the Cygwin installer, keep the recommended
+      packages that are pre-selected in the default configuration.
+   
+   2. Using the installation tools, add the following packages:
+      
+        make (GNU make)  bison        libgmp3-dev
+        gcc-core         byacc        libmpfr-dev
+        gcc-g++          gperf        libmpc-dev
+        flex             gdb          automake-1.15
+        libncurses-dev   libgmp-dev
+   
+After installing Cygwin, you will get lots of links for installed
+tools and shells.  I use the RXVT native shell.  It is fast and reliable
+and does not require you to run the Cygwin X server (which is neither
+fast nor reliable).  Unless otherwise noted, the rest of these
+instructions assume that you are at a bash command line prompt in
+either Linux or in Cygwin shell.
+
+## Using MSYS
+
+MSYS is an environment the derives from Cygwin.  Thus, most things said
+about Cygwin apply equally to MSYS.  This section will, then, focus on
+the differences when using MSYS, specifically MSYS2.
+
+Here is it assumed that you have already downloaded and installed MSYS2
+from https://www.msys2.org using the windows installer available at that
+location.  It is also assumed that you have brought in the necessary
+tools using the 'pacman' package management tool Tools needed including:
+
+  pacman -S git
+  pacman -S make
+  pacman -S gcc
+  pacman -S gdb
+
+And possibly others depending upon your usage.  Then you will need to
+build and install kconfig-frontends per the instructions of the top-level
+README.txt file in the tools repository.  This requires the following
+additional tools:
+
+    pacman -S bison
+    pacman -S gperf
+    pacman -S ncurses-devel
+    pacman -S automake-wrapper
+    pacman -S autoconf
+    pacman -S pkg-config
+
+Because of some versioning issues, I had to run 'aclocal' prior to
+running the kconfig-frontends configure script.  See "Configuring NuttX"
+below for further information.
+
+Unlike Cygwin, MSYS does not support symbolic links.  The 'ln -s' command
+will, in fact, copy a directory!  This means that you Make.defs file will
+have to include definitions like:
+
+    ifeq ($(CONFIG_WINDOWS_MSYS),y)
+      DIRLINK = $(TOPDIR)/tools/copydir.sh
+      DIRUNLINK = $(TOPDIR)/tools/unlink.sh
+    endif
+
+This will force the directory copies to work in a way that can be handled
+by the NuttX build system.  NOTE:  The default link.sh script has been
+updated so that is should now be MSYS2 compatible.  The above is preferred
+but no longer necessary in the Make.defs file.
+
+To build the simulator under MSYS, you also need:
+
+    pacman -S zlib-devel
+
+It appears that you cannot use directory names with spaces in them like
+"/c/Program\ Files \(86\)" in the MSYS path variable.  I worked around this
+by create Windows junctions like this:
+
+  1. Open the a windows command terminal,
+  
+  2. CD to `c:\msys64`, then
+  
+  3. `mklink /j programfiles "C:/Program\ Files"` and
+  
+  4. `mklink /j programfiles86 "C:/Program\ Files\ \(x86\)"`
+     
+     They then show up as `/programfiles` and `/programfiles86` with the MSYS2
+     sandbox.  Those paths can then be used with the PATH variable.  I had
+     to do something similar for the path to the GNU Tools "ARM Embedded
+     Toolchain" which also has spaces in the path name.
+
+## Ubuntu Bash under Windows 10
+
+A better version of a command-line only Ubuntu under Windows 10 (beta)
+has recently been made available from Microsoft.
+
+### Installation
+
+Installation instructions abound on the Internet complete with screen
+shots.  I will attempt to duplicate those instructions in full here.
+Here are the simplified installation steps:
+
+  - Open *Settings*.
+  
+  - Click on *Update & security*.
+  
+  - Click on *For Developers*.
+  
+  - Under *Use developer features*, select the *Developer mode* option to
+    setup the environment to install Bash.
+  
+  - A message box should pop up.  Click *Yes* to turn on developer mode.
+  
+  - After the necessary components install, you'll need to restart your
+    computer.
+    
+    Once your computer reboots:
+  
+  - Open *Control Panel*.
+  
+  - Click on *Programs*.
+  
+  - Click on *Turn Windows features on or off*.
+  
+  - A list of features will pop up, check the *Windows Subsystem for Linux
+    (beta)* option.
+  
+  - Click *OK*.
+  
+  - Once the components installed on your computer, click the *Restart
+    now* button to complete the task.
+    
+    After your computer restarts, you will notice that Bash will not appear in
+    the *Recently added* list of apps, this is because Bash isn't actually
+    installed yet. Now that you have setup the necessary components, use the
+    following steps to complete the installation of Bash:
+  
+  - Open *Start*, do a search for `bash.exe`, and press *Enter*.
+  
+  - On the command prompt, type `y` and press Enter to download and install
+    Bash from the Windows Store.  This will take awhile.
+  
+  - Then you'll need to create a default UNIX user account. This account
+    doesn't have to be the same as your Windows account. Enter the
+    username in the required field and press Enter (you can't use the
+    username `admin`).
+  
+  - Close the `bash.exe` command prompt.
+  
+  Now that you completed the installation and setup, you can open the Bash
+  tool from the Start menu like you would with any other app.
+
+### Accessing Windows Files from Ubuntu
+
+File systems will be mounted under `/mnt` so for example `C:\Program Files`
+appears at `/mnt/c/Program Files`.  This is as opposed to Cygwin where
+the same directory would appear at `/cygdrive/c/Program Files`.
+
+With these differences (perhaps a few other Windows quirks) the Ubuntu
+install works just like Ubuntu running natively on your PC.
+
+A good tip for file sharing is to use symbolic links within your Ubuntu
+home directory.  For example, suppose you have your `projects` directory
+at `C:\Documents\projects`.  Then you can set up a link to the `projects/`
+directory in your Ubuntu directory like:
+
+    ln -s /mnt/c/Documents/projects projects
+
+### Accessing Ubuntu Files From Windows
+
+In Ubuntu Userspace for Windows, the Ubuntu file system root directory is
+at:
+
+    %localappdata%\lxss\rootfs
+
+Or
+
+    C:\Users\Username\AppData\Local\lxss\rootfs
+
+However, I am unable to see my files under the rootfs\home directory.
+After some looking around, I find the home directory
+`%localappdata%\lxss\home`.
+
+With that trick access to the `/home` directory, you should actually be
+able to use Windows tools outside of the Ubuntu sandbox with versions of
+NuttX built within the sandbox using that path.
+
+### Executing Windows Tools from Ubuntu
+
+You can also execute Windows tools from within the Ubuntu sandbox:
+
+    /mnt/c/Program\ Files\ \(x86\)/Microchip/xc32/v1.43/bin/xc32-gcc.exe --version
+    Unable to translate current working directory. Using C:\WINDOWS\System32
+    xc32-gcc.exe (Microchip Technology) 4.8.3 MPLAB XC32 Compiler v1.43 Build date: Mar  1 2017
+    ...
+
+The error message indicates that there are more issues:  You cannot mix
+Windows tools that use Windows style paths in an environment that uses
+POSIX paths.  I think you would have to use Linux tools only from within
+the Ubuntu sandbox.
+
+### Install Ubuntu Software
+
+Use `sudo apt-get install <package name>`.  As examples, this is how
+you would get GIT:
+
+    sudo apt-get install git
+
+This will get you a compiler for your host PC:
+
+    sudo apt-get install gcc
+
+This will get you an ARM compiler for your target:
+
+    sudo apt-get install gcc-arm-none-eabi
+
+**NOTE**: That is just an example.  I am not sure if apt-get will give you a
+current or usable compiler.  You should carefully select your toolchain
+for the needs of your project.
+
+You will also need to get the kconfig-frontends configuration as
+described below under *NuttX Configuration Tool*.  In order to build the
+kconfig-frontends configuration tool you will also need: `make`, `gperf`,
+`flex`, `bison`, and `libncurses-dev`.
+
+That is enough to do a basic NuttX build.
+
+### Integrating with Windows Tools
+
+If you want to integrate with Windows native tools, then you would need
+deal with the same kind of craziness as with integrating Cygwin with
+native toolchains, see the section *Cygwin Build Problems* below.
+
+However, there is currently no build support for using Windows native
+tools with Ubuntu under Windows.  This tool combination is made to work
+with Cygwin through the use of the `cygpath -w` tool that converts paths
+from say `/cydrive/c/Program Files` to `C:\Program Files`.  There is,
+however, no corresponding tool to convert `/mnt/c/Program Files` in the
+Ubuntu environment.
+
+### Graphics Support
+
+The Ubuntu version support by Microsoft is a command-line only version.
+There is no support for Linux graphics utilities.
+
+This limitation is not a limitation of Ubuntu, however, only in what
+Microsoft is willing to support.  If you install a X-Server, then you
+can also use basic graphics utilities.  See for example:
+
+  <http://www.howtogeek.com/261575/how-to-run-graphical-linux-desktop-applications-from-windows-10s-bash-shell/>
+
+Many Linux graphics programs would, however, also require a graphics
+framework like GTK or Qt.  So this might be a trip down the rabbit hole.
+
+### Using macOS
+
+You need to install at least the following tools specific to macOS.
+
+  * flock (used by APPDIR build logic)
+    
+A macOS port is available at: <https://github.com/discoteq/flock>
+  
+    brew tap discoteq/discoteq
+    brew install flock
+  
+  If you want to build the sim:
+
+  * Xcode (the native compiler and the rest of the toolchain)
+
+  * ELF toolchain (if you want to build modules for CONFIG_LIBC_MODLIB)
+
+    brew install x86_64-elf-gc
+
+# INSTALLATION
+
+There are two ways to get NuttX:  You may download released, stable
+tarballs from either the project website.  Or you may get NuttX by
+cloning the GIT repositories.  Let's consider the released tarballs
+first:
+
+## Download and Unpack
+
+Download and unpack the NuttX tarball.  If you are reading this, then
+you have probably already done that.  After unpacking, you will end
+up with a directory called nuttx-version (where version is the NuttX
+version number). You might want to rename that directory nuttx to
+match the various instructions in the documentation and some scripts
+in the source tree.
+
+  * Download location:
+  
+    <https://nuttx.apache.org/download/>
+  
+  * Legacy download locations:
+
+    <https://bitbucket.org/nuttx/nuttx/downloads>  
+    <https://sourceforge.net/projects/nuttx/files/nuttx/>
+
+## Semi-Optional apps/ Package
+
+All NuttX libraries and example code used to be in included within
+the NuttX source tree.  As of NuttX-6.0, this application code was
+moved into a separate tarball, the apps tarball.  If you are just
+beginning with NuttX, then you will want to download the versioned
+apps tarball along with the NuttX tarball.  If you already have your
+own product application directory, then you may not need the apps
+tarball.
+
+It is called "Semi-optional" because if you don't have some `apps/`
+directory, NuttX will *fail* to build! You do not necessarily need
+to use the NuttX apps tarball but may, instead, provide your own
+custom application directory.  Such a custom directory would need
+to include a valid Makefile to support the build and a valid Kconfig
+file to support the configuration.  More about these files later.
+
+Download then unpack the apps tarball in the same directory where you
+unpacked the NuttX tarball.  After you unpack the apps tarball, you
+will have a new directory called apps-version (where the version
+should exactly match the version of the NuttX tarball).  Again, you
+might want to rename the directory to simply apps/ to match what
+you read in the documentation
+
+After unpacking (and renaming) the apps tarball, you will have two
+directories side by side like this:
+
+             |
+        +----+----+
+        |         |
+      nuttx/     apps/
+
+This is important because the NuttX build will expect to find the
+apps directory in that (default) location.  That default location
+can be changed by modifying your NuttX configuration file, but that
+is another story.
+
+## Installation Directories with Spaces in the Path
+
+The nuttx build directory should reside in a path that contains no
+spaces in any higher level directory name.  For example, under
+Cygwin, your home directory might be formed from your first and last
+names like: `/home/First Last`. That will cause strange errors when
+the make system tries to build.
+
+[Actually, that problem is probably not too difficult to fix.  Some
+ Makefiles probably just need some paths within double quotes]
+
+I work around spaces in the home directory name, by creating a
+new directory that does not contain any spaces, such as `/home/nuttx`.
+Then I install NuttX in `/home/nuttx` and always build from
+`/home/nuttx/nuttx-code`.
+
+## Downloading from Repositories
+
+### Cloning the Repository
+
+**BEFORE** cloning repositories on any Windows platform do the following GIT
+command:
+
+    git config --global core.autocrlf false
+
+That will avoid conversions of linefeeds (newlines, \n) to carriage
+return plus linefeed sequences (\r\n)
+
+The current NuttX du jour is available in from a GIT repository.  Here are
+instructions for cloning the core NuttX RTOS (corresponding to the nuttx
+tarball discussed above):
+
+    git clone https://gitbox.apache.org/repos/asf/incubator-nuttx.git nuttx
+
+-or-
+
+    git clone https://github.com/apache/incubator-nuttx.git nuttx
+
+And the semi-optional apps/ application directory and be cloned like:
+
+    git clone https://gitbox.apache.org/repos/asf/incubator-nuttx-apps.git apps
+  
+-or-
+  
+    git clone https://github.com/apache/incubator-nuttx-apps.git apps
+
+That will give you the same directory structure like this:
+    
+             |
+        +----+----+
+        |         |
+      nuttx/     apps/
+
+### Configuring the Clones
+
+The following steps need to be performed for each of the repositories.
+After changing to the clone directory:
+
+Set your identity:
+
+    git config --global user.name "My Name"
+    git config --global user.email my.name@example.com
+  
+Colorized diffs are much easier to read:
+
+    git config --global color.branch auto
+    git config --global color.diff auto
+    git config --global color.interactive auto
+    git config --global color.status auto
+
+Checkout other settings
+
+    git config --list
+
+### Cloning NuttX Inside Cygwin
+
+If you are cloning the NuttX repository, it is recommended to avoid
+automatic end of lines conversions by git. These conversions may break
+some scripts like configure.sh. Before cloning, do the following:
+
+    git config --global core.autocrlf false
+
+## Related Repositories
+
+These are standalone repositories:
+
+  * <https://gitbox.apache.org/repos/asf/incubator-nuttx-apps>  
+    or  
+    <https://github.com/apache/incubator-nuttx-apps.git>
+    
+    This directory holds an optional package of applications and libraries
+    can be used with the NuttX RTOS.  There is a README.txt file there that
+    will provide more information about that package.
+
+  * <https://bitbucket.org/nuttx/nxwidgets>
+  
+    This is the NuttX C++ graphics support.  This includes NxWM, the tiny
+    NuttX Window Manager.
+
+  * <https://bitbucket.org/nuttx/uclibc>
+  
+    This repository contains a version of the uClibc++ C++ library.  This code
+    originates from <http://cxx.uclibc.org/> and has been adapted for NuttX by the
+    RGMP team (<http://rgmp.sourceforge.net/wiki/index.php/Main_Page>).
+
+  * <https://bitbucket.org/nuttx/buildroot>
+  
+    A environment that you can to use to build a custom, NuttX GNU toolchain.
+
+  * <https://bitbucket.org/nuttx/tools>
+  
+    There are snapshots of some tools here that you will need to work with
+    NuttX:  kconfig-frontends, genromfs, and others.
+
+## Notes about Header Files
+
+### Other C-Library Header Files
+
+When a GCC toolchain is built, it must be built against a C library.
+The compiler together with the contents of the C library completes the
+C language definition and provides the complete C development
+environment.  NuttX provides its own, built-in C library.  So the
+complete, consistent C language definition for use with NuttX comes from
+the combination of the compiler and the header files provided by the
+NuttX C library.
+
+When a GCC toolchain is built, it incorporates the C library header
+files into the compiler internal directories and, in this way, the C
+library really becomes a part of the toolchain.  If you use the NuttX
+buildroot toolchain as described below under "NuttX Buildroot
+Toolchain", your GCC toolchain will build against the NuttX C library
+and will incorporate the NuttX C library header files as part of the
+toolchain.
+
+If you use some other, third-party tool chain, this will not be the
+case, however.  Those toolchains were probably built against some
+other, incompatible C library distribution (such as newlib).  Those
+tools will have incorporated the incompatible C library header files
+as part of the toolchain.  These incompatible header files must *not*
+be used with NuttX because they will conflict with definitions in the
+NuttX built-in C-Library.  For such toolchains that include header
+files from a foreign C-Library, NuttX must be compiled without using
+the standard header files that are distributed with your toolchain.
+This prevents including conflicting, incompatible header files such
+as stdio.h.
+
+The math.h and stdarg.h are probably the two most trouble some header
+files to deal with.  These troublesome header files are discussed in
+more detail below.
+
+### Header Files Provided by Your Toolchain
+
+Certain header files, such as `setjmp.h`, `stdarg.h`, and `math.h`, may still
+be needed from your toolchain and your compiler may not, however, be able
+to find these if you compile NuttX without using standard header files
+(i.e., with `-nostdinc`).  If that is the case, one solution is to copy
+those header file from your toolchain into the NuttX include directory.
+
+### Duplicated Header Files
+
+There are also a few header files that can be found in the `nuttx/include`
+directory which are duplicated by the header files from your toolchain.
+stdint.h and stdbool.h are examples.  If you prefer to use the `stdint.h`
+and `stdbool.h` header files from your toolchain, those could be copied
+into the `nuttx/include/` directory. Using most other header files from
+your toolchain would probably cause errors.
+
+### math.h
+
+Even though you should not use a foreign C-Library, you may still need
+to use other, external libraries with NuttX.  In particular, you may
+need to use the math library, libm.a.  NuttX supports a generic, built-in
+math library that can be enabled using `CONFIG_LIBM=y`.  However, you may
+still want to use a higher performance external math library that has
+been tuned for your CPU.  Sometimes such tuned math libraries are
+bundled with your toolchain.
+
+The math library header file, `math.h`, is a then special case.  If you do
+nothing, the standard math.h header file that is provided with your
+toolchain will be used.
+
+If you have a custom, architecture specific math.h header file, then
+that header file should be placed at `arch/<cpu>/include/math.h`.  There
+is a stub `math.h` header file located at `include/nuttx/lib/math.h`.  This stub
+header file can be used to "redirect" the inclusion to an architecture-
+specific math.h header file.  If you add an architecture specific math.h
+header file then you should also define `CONFIG_ARCH_MATH_H=y` in your
+NuttX Configuration file.  If `CONFIG_ARCH_MATH_H` is selected, then the
+top-level Makefile will copy the stub math.h header file from
+`include/nuttx/lib/math.h` to `include/math.h` where it will become the system
+`math.h` header file.  The stub `math.h` header file does nothing other
+than to include that architecture-specific `math.h` header file as the
+system `math.h` header file.
+
+### float.h
+
+If you enable the generic, built-in math library, then that math library
+will expect your toolchain to provide the standard `float.h` header file.
+The float.h header file defines the properties of your floating point
+implementation.  It would always be best to use your toolchain's `float.h`
+header file but if none is available, a default `float.h` header file will
+be provided if this option is selected.  However, there is no assurance
+that the settings in this `float.h` are actually correct for your platform!
+
+### stdarg.h
+
+In most cases, the correct version of stdarg.h is the version provided
+with your toolchain.  However, sometimes there are issues with
+using your toolchains `stdarg.h`.  For example, it may attempt to draw in
+header files that do not exist in NuttX or perhaps the header files that
+it uses are not compatible with the NuttX header files.  In those cases,
+you can use an architecture-specific `stdarg.h` header file by defining
+`CONFIG_ARCH_STDARG_H=y`.
+
+See the discussion above for the `math.h` header.  This setting works
+exactly the same for the `stdarg.h` header file.
+
+# CONFIGURING NUTTX
+
+## Instantiating "Canned" Configurations
+
+### `configure.sh` and `configure.bat`
+
+"Canned" NuttX configuration files are retained in:
+
+    boards/<arch-name>/<chip-name>/<board-name>/configs/<config-dir>
+
+Where `<board-name>` is the name of your development board and `<config-dir>`
+is the name of the sub-directory containing a specific configuration for
+that board. `<arch-name>` and `<chip-name>` refer to characteristics of the
+MCU used on the board: `<arch-name>` is the CPU architecture implemented
+by the MCU; `<chip-name>` identifies the MCU chip family.  Only a few
+steps are required to instantiate a NuttX configuration, but to make the
+configuration even easier there are scripts available in the tools/
+sub-directory combines those simple steps into one command.
+
+There is one tool for use with any Bash-like shell that does configuration
+steps.  It is used as follows:
+
+    tools/configure.sh <board-name>:<config-dir>
+
+There is an alternative Windows batch file that can be used in the windows
+native environment like:
+
+    tools\configure.bat <board-name>:<config-dir>
+
+And, to make sure that other platforms are supported, there is also a
+C program at tools/configure.c that can be compiled to establish the
+board configuration.
+
+See `tools/README.txt` for more information about these scripts.
+
+General information about configuring NuttX can be found in:
+
+    {TOPDIR}/boards/README.txt
+    {TOPDIR}/boards/<arch-name>/<chip-name>/<board-name>/README.txt
+
+### The Hidden Configuration Scripts:
+
+As mentioned above, there are only a few simple steps to instantiating a
+NuttX configuration.  Those steps are hidden by the configuration scripts
+but are summarized below:
+  
+  1. Copy Files
+  
+     Configuring NuttX requires only copying two files from the
+     `<config-dir>` to the directory where you installed NuttX (TOPDIR):
+  
+       * Copy `boards/<arch-name>/<chip-name>/<board-name>/configs/<config-dir>/Make.def` to `{TOPDIR}/Make.defs`
+    
+         OR
+    
+       * Copy `boards/<arch-name>/<chip-name>/<board-name>/scripts/Make.def`
+         to `{TOPDIR}/Make.defs`
+    
+         Make.defs describes the rules needed by your tool chain to compile
+         and link code.  You may need to modify this file to match the
+         specific needs of your toolchain.  NOTE that a configuration may
+         have its own unique Make.defs file in its configuration directory or
+         it may use a common Make.defs file for the board in the scripts/
+         directory.  The first takes precedence.
+    
+       * Copy `boards/<arch-name>/<chip-name>/<board-name>/configs/<config-dir>/defconfig` to `{TOPDIR}/.config`
+    
+         The defconfig file holds the actual build configuration.  This
+         file is included by all other make files to determine what is
+         included in the build and what is not.  This file is also used
+         to generate a C configuration header at `include/nuttx/config.h`.
+    
+       * Copy other, environment-specific files to `{TOPDIR}`
+    
+         This might include files like .gdbinit or IDE configuration files
+         like .project or .cproject.
+  
+  2. Refresh the Configuration
+  
+     New configuration setting may be added or removed.  Existing settings
+     may also change there values or options.  This must be handled by
+     refreshing the configuration as described below.
+    
+     NOTE:  NuttX uses only compressed defconfig files.  For the NuttX
+     defconfig files, this refreshing step is *NOT* optional; it is also
+     necessary to uncompress and regenerate the full making file.  This is
+     discussed further below.
+
+## Refreshing Configurations
+
+Configurations can get out of date.  As new configuration settings are
+added or removed or as dependencies between configuration settings
+change, the contents of a default configuration can become out of synch
+with the build systems.  Hence, it is a good practice to "refresh" each
+configuration after configuring and before making.  To refresh the
+configuration, use the NuttX Configuration Tool like this:
+
+    make oldconfig
+
+AFTER you have instantiated the NuttX configuration as described above.
+The configuration step copied the .config file into place in the top-level
+NuttX directory; 'make oldconfig' step will then operate on that .config
+file to bring it up-to-date.
+
+If your configuration is out of date, you will be prompted by 'make oldconfig'
+to resolve the issues detected by the configuration tool, that is, to
+provide values for the new configuration options in the build system.  Doing
+this can save you a lot of problems down the road due to obsolete settings in
+the default board configuration file.  The NuttX configuration tool is
+discussed in more detail in the following paragraph.
+
+Confused about what the correct value for a new configuration item should
+be?  Enter ? in response to the 'make oldconfig' prompt and it will show
+you the help text that goes with the option.
+
+If you don't want to make any decisions are willing to just accept the
+recommended default value for each new configuration item, an even easier
+way is:
+
+    make olddefconfig
+
+The olddefconfig target will simply bring your configuration up to date with
+the current Kconfig files, setting any new options to the default value.
+No questions asked.
+
+## NuttX Configuration Tool
+
+An automated tool has been incorporated to support re-configuration
+of NuttX.  This tool is based on the kconfig-frontends application available
+at <https://bitbucket.org/nuttx/tools/src/master/kconfig-frontends/>.  (This
+is a snapshot of the old <http://ymorin.is-a-geek.org/projects/kconfig-frontends>
+which is no longer available.)  This application provides a tool called
+`kconfig-mconf` that is used by the NuttX top-level Makefile. The following
+make target is provided:
+
+    make menuconfig
+
+This make target will bring up NuttX configuration menus.
+
+**WARNING**:  Never do `make menuconfig` on a configuration that has
+not been converted to use the kconfig-frontends tools!  This will
+damage your configuration (see
+<http://www.nuttx.org/doku.php?id=wiki:howtos:convertconfig>).
+
+How do we tell a new configuration from an old one? See "Incompatibilities
+with Older Configurations" below.
+
+The `menuconfig` make target depends on two things:
+
+  1. The Kconfig configuration data files that appear in almost all
+     NuttX directories.  These data files are the part that is still
+     under development (patches are welcome!).  The Kconfig files
+     contain configuration information for the configuration settings
+     relevant to the directory in which the Kconfig file resides.
+     
+     NOTE: For a description of the syntax of this configuration file,
+     see kconfig-language.txt in the tools repository at
+     <https://bitbucket.org/nuttx/tools>
+  
+  2. The `kconfig-mconf` tool. `kconfig-mconf` is part of the
+     kconfig-frontends package.  You can download that package from the
+     snapshot in the tools repository at <https://bitbucket.org/nuttx/tools>.
+  
+     Building kconfig-frontends under Linux may be as simple as
+     `configure; make; make install` but there may be some build
+     complexities, especially if you are building under Cygwin.  See
+     the more detailed build instructions in the top-level README.txt
+     file of the tools repository at <https://bitbucket.org/nuttx/tools>.
+  
+  
+     The `make install` step will, by default, install the `kconfig-mconf`
+     tool at `/usr/local/bin/mconf`.  Where ever you choose to
+     install `kconfig-mconf`, make certain that your PATH variable includes
+     a path to that installation directory.
+  
+     The kconfig-frontends tools will not build in a native Windows
+     environment directly "out-of-the-box".  For the Windows native
+     case, you can use the modified version of kconfig-frontends
+     that can be found at
+
+     <http://uvc.de/posts/linux-kernel-configuration-tool-kconfig-under-windows.html>  
+
+     or a more recent port that can be found at  
+
+     <http://reclonelabs.com/more-kconfig-awesomeness-for-windows/>.
+   
+The basic configuration order is "bottom-up":
+   
+   - Select the build environment,
+   - Select the processor,
+   - Select the board,
+   - Select the supported peripherals
+   - Configure the device drivers,
+   - Configure the application options on top of this.
+   
+This is pretty straight forward for creating new configurations
+but may be less intuitive for modifying existing configurations.
+
+Another ncurses-based tool that is an option to kconfig-mconf is
+kconfig-nconf.  The differences are primary in in the aesthetics of the
+UI.  If you have kconfig-nconf built, then you can invoke that front end
+with:
+   
+     make nconfig
+   
+If you have an environment that supports the Qt or GTK graphical systems
+(probably KDE or gnome, respectively, or Cygwin under Windows with Qt or
+GTK installed), then you can also build the graphical kconfig-frontends,
+kconfig-qconf and kconfig-gconf.  In these case, you can start the
+graphical configurator with either:
+   
+     make qconfig
+   
+ or
+   
+     make gconfig
+   
+Some keyboard shortcuts supported by kconfig-mconf, the tool that runs
+when you do 'make menuconfig':
+
+   - `?` will bring up the mconfig help display.
+   
+   - `/` can be used find configuration selections.
+   
+   - `Z` can be used to reveal hidden configuration options
+   
+These last two shortcuts are described further in the following
+paragraphs.
+
+## Finding Selections in the Configuration Menus
+
+The NuttX configuration options have gotten complex and it can be very
+difficult to find options in the menu trees if you are not sure where
+to look.  The "basic configuration order" describe above can help to
+narrow things down.
+
+But if you know exactly what configuration setting you want to select,
+say CONFIG_XYZ, but not where to find it, then the 'make menuconfig'

Review comment:
       @v01d also use backticks on `make menuconfig`

##########
File path: README.md
##########
@@ -0,0 +1,2513 @@
+# APACHE NUTTX (INCUBATING)
+
+* Introduction
+  - Incubation Status
+* Community
+  - Getting Help
+  - Mailing Lists
+  - Issue Tracker
+  - Source Code
+  - Website Source Code
+* Environments
+  - Installing Cygwin
+  - Ubuntu Bash under Windows 10
+  - Using macOS
+* Installation
+  - Download and Unpack
+  - Semi-Optional apps/ Package
+  - Installation Directories with Spaces in the Path
+  - Downloading from Repositories
+  - Related Repositories
+  - Notes about Header Files
+* Configuring NuttX
+  - Instantiating "Canned" Configurations
+  - Refreshing Configurations
+  - NuttX Configuration Tool
+  - Finding Selections in the Configuration Menus
+  - Reveal Hidden Configuration Options
+  - Make Sure that You are on the Right Platform
+  - Comparing Two Configurations
+  - Making defconfig Files
+  - Incompatibilities with Older Configurations
+  - NuttX Configuration Tool under DOS
+* Toolchains
+  - Cross-Development Toolchains
+  - NuttX Buildroot Toolchain
+* Shells
+* Building NuttX
+  - Building
+  - Re-building
+  - Build Targets and Options
+  - Native Windows Build
+  - Installing GNUWin32
+* Cygwin Build Problems
+  - Strange Path Problems
+  - Window Native Toolchain Issues
+* Documentation
+
+# INTRODUCTION
+
+Apache NuttX (Incubating) is a real-time operating system (RTOS) with an
+emphasis on standards compliance and small footprint.  Scalable from 8-bit
+to 32-bit microcontroller environments, the primary governing standards in
+NuttX are POSIX and ANSI standards. Additional standard APIs from Unix and
+other common RTOSs (such as VxWorks) are adopted for functionality not
+available under these standards, or for functionality that is not
+appropriate for deeply-embedded environments (such as fork()).
+
+Extensive documentation can be found on the project wiki:
+  <https://cwiki.apache.org/NUTTX/Nuttx>
+
+## Incubation Status
+
+Apache NuttX (Incubating) is an effort undergoing Incubation at The Apache
+Software Foundation (ASF), sponsored by the Incubator.  For more on our
+incubation effort, please see the file DISCLAIMER-WIP, in the same
+directory as this README.
+
+For brevity, the rest of this file will refer to it as Apache NuttX or
+simply NuttX.
+
+# COMMUNITY
+
+Every volunteer project obtains its strength from the people involved in
+it.  We invite you to participate as much or as little as you choose.
+
+We encourage you to:
+
+  - Use our project and provide feedback.
+  - Provide us with use-cases.
+  - Report bugs and submit patches.
+  - Contribute code or documentation.
+
+## Getting Help
+
+The best place to get help is the developer's mailing list.  Please see
+the following section:
+
+## Mailing Lists
+
+Get help using NuttX or contribute to the project on our mailing lists:
+
+  * <de...@nuttx.apache.org> is for people who want to contribute code to NuttX.
+    * To subscribe, send an email to <de...@nuttx.apache.org>.
+    * To unsubscribe, send an email to <de...@nuttx.apache.org>.
+    * View the archives at:
+      <https://www.mail-archive.com/dev@nuttx.apache.org/>
+
+  * <co...@nuttx.apache.org> is a read-only list that notifies subscribers
+  about commit messages and patches to NuttX.
+    * To subscribe, send an email to <co...@nuttx.apache.org>.
+    * To unsubscribe, send an email to <co...@nuttx.apache.org>.
+    * View the archives at:
+      <https://www.mail-archive.com/commits@nuttx.apache.org/>
+
+## Issue Tracker
+
+### Bug Reports:
+
+Found bug? Send an email to the dev list: <de...@nuttx.apache.org>
+
+Before submitting an issue, please:
+
+  - Verify that the bug does in fact exist. 
+  
+  - Search the mailing list archives to verify there is no existing issue
+    reporting the bug you've found.
+ 
+  - Consider tracking down the bug yourself in the NuttX source code and
+    submitting a patch along with your bug report.  This is a great time
+    saver for the NuttX developers and helps ensure the bug will be fixed
+    quickly.
+  
+### Feature Requests:
+  
+Enhancement requests for new features are also welcome. The more concrete
+and rational the request is, the greater the chance it will incorporated
+into future releases.
+
+## Source Code
+
+The project sources are in two Git repositories.  The core OS is in
+incubator-nuttx and the apps repository is in incubator-nuttx-apps.  These
+are housed in GitBox on ASF servers and also mirrored at GitHub.  These
+are kept in sync, so you can use whichever option you prefer.
+
+  - NuttX core OS repository:
+    
+    - Primary:
+      <https://gitbox.apache.org/repos/asf?p=incubator-nuttx.git>
+    
+    - GitHub Mirror:
+      <https://github.com/apache/incubator-nuttx>
+  
+  - Apps repository:
+    
+    - Primary:
+      <https://gitbox.apache.org/repos/asf?p=incubator-nuttx-apps.git>
+    
+    - GitHub Mirror:
+      <https://github.com/apache/incubator-nuttx-apps>
+
+## Website Source Code
+
+The project website sources are accessible via the website source code
+  repository which is also mirrored in GitHub:
+
+- Primary:
+  <https://gitbox.apache.org/repos/asf?p=incubator-nuttx-website.git>
+
+- GitHub Mirror:
+  <https://github.com/apache/incubator-nuttx-website>
+
+# ENVIRONMENTS
+
+  NuttX requires a POSIX development environment such as you would find under
+  Linux or macOS.  NuttX may also be installed and built on Windows system
+  if you also provide such a POSIX development environment.  Options for a
+  POSIX development environment under Windows include:
+
+  - An installation of Linux on a virtual machine (VM) in Windows.  I have
+    not been happy using a VM myself.  I have had stability problems with
+    open source VMs and commercial VMs cost more than I want to spend.
+    Sharing files with Linux running in a VM is awkward;  sharing devices
+    connected to the Windows box with Linux in a VM is, at the very least,
+    confusing;  Using Windows tools (such as Segger J-Link) with files
+    built under the Linux VM is not a possibility.
+
+  - The Cygwin environment.  Instructions for installation of Cygwin on a
+    Windows system are provided in the following paragraph, "Installing
+    Cygwin".  Cygwin is a mature, well-tested, and very convenient
+    environment.  It is especially convenient if you  need to
+    integrate with Windows tools and files.  Downsides are that the
+    installation time is very long and the compile times are slow.
+
+  - Ubuntu/Bash shell under Windows 10.  This is a new option under
+    Windows 10.  See the section "Ubuntu Bash under Windows 10" below.
+    This is an improvement over Cygwin if your concern is compile time;
+    its build performance is comparable to native Linux, certainly better
+    than the Cygwin build time.  It also installs in a tiny fraction of
+    the time as Cygwin, perhaps 20 minutes for the basic Ubuntu install
+    (vs. more than a day for the complete Cygwin install).
+  
+    There have been even more recent ports of Linux environment to
+    Windows.  I need to update this section to include some mention of
+    these alternatives.
+
+  - The MSYS environment.  MSYS derives from an older version of Cygwin
+    simplified and adapted to work more naturally in the Windows
+    environment.  See <http://www.mingw.org/wiki/MSYS> if you are
+    interested in using MSYS.  The advantages of the MSYS environment is
+    that it is better integrted with the native Windows environment and
+    lighter weight; it uses only a  minimal number of add-on POSIX-land
+    tools.
+  
+    The download link in that Wiki takes you to the SourceForge download
+    site.  The SourceForge MSYS project has been stagnant for some time.
+    The MSYS project has more recently moved to
+    <http://odsn.net/projects/sfnet_mingwbundle>.  Downloads of current .zip
+    files are available there but no instructions for the installation.
+
+  - MSYS2 appears to be a re-write of MSYS based on a newer version of
+    Cygwin.  Is it available at <https://www.msys2.org>.  A windows
+    installer is available at that site along with very good installation
+    instructions.  The download is relatively quick (at least compared to
+    Cygwin) and the 'pacman' package management tool supports supports
+    simple system updates.  For example, 'pacman -S git' will install the
+    GIT command line utilities.
+
+  - Other POSIX environments.  Check out:
+    
+    - UnxUtils: <https://sourceforge.net/projects/unxutils/>,
+      <https://en.wikipedia.org/wiki/UnxUtils>
+    - MobaXterm: <https://mobaxterm.mobatek.net/>
+    - Gow: <https://github.com/bmatzelle/gow/wiki>
+  
+    **Disclaimer**:  In principle, these should work.  However, I have never
+    used any of these environments and cannot guarantee that there is
+    not some less-than-obvious issues.
+  
+NuttX can also be installed and built on a native Windows system, but with
+some potential tool-related issues (see the discussion "Native Windows
+Build" under "Building NuttX" below).  GNUWin32 is used to provide
+compatible native windows tools.
+
+## Installing Cygwin
+
+Installing Cygwin on your Windows PC is simple, but time consuming.  See
+<http://www.cygwin.com/> for installation instructions. Basically you just
+need to download a tiny setup.exe program and it does the real, network
+installation for you.
+
+Some Cygwin installation tips:
+
+  1. Install at `C:\cygwin`
+  
+  2. Install **everything**:  "Only the minimal base packages from the
+     Cygwin distribution are installed by default. Clicking on categories
+     and packages in the setup.exe package installation screen will
+     provide you with the ability to control what is installed or updated.
+     Clicking on the "Default" field next to the "All" category will
+     provide you with the opportunity to install every Cygwin package.
+     Be advised that this will download and install hundreds of megabytes
+     to your computer."
+   
+If you use the "default" installation, you will be missing many
+of the Cygwin utilities that you will need to build NuttX.  The
+build will fail in numerous places because of missing packages.
+
+NOTE: The last time I installed **everything**, the download was
+about 5GiB.  The server I selected was also very slow so it took
+over a day to do the whole install!
+
+NOTE: You don't really have to install **everything** but I cannot
+answer the question "Then what should I install?"  I don't know
+the answer to that and so will continue to recommend installing
+**everything**.
+
+You should certainly be able to omit "Science", "Math", and
+"Publishing".  You can try omitting KDE, Gnome, GTK, and other
+graphics packages if you don't plan to use them.
+
+Perhaps a minimum set would be those packages listed below for the
+"Ubuntu Bash under Windows 10" installation?
+
+**UPDATE**:  Sergey Frolov had success with the following minimal
+Cygwin configuration:
+   
+   1. After starting the Cygwin installer, keep the recommended
+      packages that are pre-selected in the default configuration.
+   
+   2. Using the installation tools, add the following packages:
+      
+        make (GNU make)  bison        libgmp3-dev
+        gcc-core         byacc        libmpfr-dev
+        gcc-g++          gperf        libmpc-dev
+        flex             gdb          automake-1.15
+        libncurses-dev   libgmp-dev
+   
+After installing Cygwin, you will get lots of links for installed
+tools and shells.  I use the RXVT native shell.  It is fast and reliable
+and does not require you to run the Cygwin X server (which is neither
+fast nor reliable).  Unless otherwise noted, the rest of these
+instructions assume that you are at a bash command line prompt in
+either Linux or in Cygwin shell.
+
+## Using MSYS
+
+MSYS is an environment the derives from Cygwin.  Thus, most things said
+about Cygwin apply equally to MSYS.  This section will, then, focus on
+the differences when using MSYS, specifically MSYS2.
+
+Here is it assumed that you have already downloaded and installed MSYS2
+from https://www.msys2.org using the windows installer available at that
+location.  It is also assumed that you have brought in the necessary
+tools using the 'pacman' package management tool Tools needed including:
+
+  pacman -S git
+  pacman -S make
+  pacman -S gcc
+  pacman -S gdb
+
+And possibly others depending upon your usage.  Then you will need to
+build and install kconfig-frontends per the instructions of the top-level
+README.txt file in the tools repository.  This requires the following
+additional tools:
+
+    pacman -S bison
+    pacman -S gperf
+    pacman -S ncurses-devel
+    pacman -S automake-wrapper
+    pacman -S autoconf
+    pacman -S pkg-config
+
+Because of some versioning issues, I had to run 'aclocal' prior to
+running the kconfig-frontends configure script.  See "Configuring NuttX"
+below for further information.
+
+Unlike Cygwin, MSYS does not support symbolic links.  The 'ln -s' command
+will, in fact, copy a directory!  This means that you Make.defs file will
+have to include definitions like:
+
+    ifeq ($(CONFIG_WINDOWS_MSYS),y)
+      DIRLINK = $(TOPDIR)/tools/copydir.sh
+      DIRUNLINK = $(TOPDIR)/tools/unlink.sh
+    endif
+
+This will force the directory copies to work in a way that can be handled
+by the NuttX build system.  NOTE:  The default link.sh script has been
+updated so that is should now be MSYS2 compatible.  The above is preferred
+but no longer necessary in the Make.defs file.
+
+To build the simulator under MSYS, you also need:
+
+    pacman -S zlib-devel
+
+It appears that you cannot use directory names with spaces in them like
+"/c/Program\ Files \(86\)" in the MSYS path variable.  I worked around this
+by create Windows junctions like this:
+
+  1. Open the a windows command terminal,
+  
+  2. CD to `c:\msys64`, then

Review comment:
       ```suggestion
     2. cd to `c:\msys64`, then
   ```

##########
File path: README.md
##########
@@ -0,0 +1,2513 @@
+# APACHE NUTTX (INCUBATING)
+
+* Introduction
+  - Incubation Status
+* Community
+  - Getting Help
+  - Mailing Lists
+  - Issue Tracker
+  - Source Code
+  - Website Source Code
+* Environments
+  - Installing Cygwin
+  - Ubuntu Bash under Windows 10
+  - Using macOS
+* Installation
+  - Download and Unpack
+  - Semi-Optional apps/ Package
+  - Installation Directories with Spaces in the Path
+  - Downloading from Repositories
+  - Related Repositories
+  - Notes about Header Files
+* Configuring NuttX
+  - Instantiating "Canned" Configurations
+  - Refreshing Configurations
+  - NuttX Configuration Tool
+  - Finding Selections in the Configuration Menus
+  - Reveal Hidden Configuration Options
+  - Make Sure that You are on the Right Platform
+  - Comparing Two Configurations
+  - Making defconfig Files
+  - Incompatibilities with Older Configurations
+  - NuttX Configuration Tool under DOS
+* Toolchains
+  - Cross-Development Toolchains
+  - NuttX Buildroot Toolchain
+* Shells
+* Building NuttX
+  - Building
+  - Re-building
+  - Build Targets and Options
+  - Native Windows Build
+  - Installing GNUWin32
+* Cygwin Build Problems
+  - Strange Path Problems
+  - Window Native Toolchain Issues
+* Documentation
+
+# INTRODUCTION
+
+Apache NuttX (Incubating) is a real-time operating system (RTOS) with an
+emphasis on standards compliance and small footprint.  Scalable from 8-bit
+to 32-bit microcontroller environments, the primary governing standards in
+NuttX are POSIX and ANSI standards. Additional standard APIs from Unix and
+other common RTOSs (such as VxWorks) are adopted for functionality not
+available under these standards, or for functionality that is not
+appropriate for deeply-embedded environments (such as fork()).
+
+Extensive documentation can be found on the project wiki:
+  <https://cwiki.apache.org/NUTTX/Nuttx>
+
+## Incubation Status
+
+Apache NuttX (Incubating) is an effort undergoing Incubation at The Apache
+Software Foundation (ASF), sponsored by the Incubator.  For more on our
+incubation effort, please see the file DISCLAIMER-WIP, in the same
+directory as this README.
+
+For brevity, the rest of this file will refer to it as Apache NuttX or
+simply NuttX.
+
+# COMMUNITY
+
+Every volunteer project obtains its strength from the people involved in
+it.  We invite you to participate as much or as little as you choose.
+
+We encourage you to:
+
+  - Use our project and provide feedback.
+  - Provide us with use-cases.
+  - Report bugs and submit patches.
+  - Contribute code or documentation.
+
+## Getting Help
+
+The best place to get help is the developer's mailing list.  Please see
+the following section:
+
+## Mailing Lists
+
+Get help using NuttX or contribute to the project on our mailing lists:
+
+  * <de...@nuttx.apache.org> is for people who want to contribute code to NuttX.
+    * To subscribe, send an email to <de...@nuttx.apache.org>.
+    * To unsubscribe, send an email to <de...@nuttx.apache.org>.
+    * View the archives at:
+      <https://www.mail-archive.com/dev@nuttx.apache.org/>
+
+  * <co...@nuttx.apache.org> is a read-only list that notifies subscribers
+  about commit messages and patches to NuttX.
+    * To subscribe, send an email to <co...@nuttx.apache.org>.
+    * To unsubscribe, send an email to <co...@nuttx.apache.org>.
+    * View the archives at:
+      <https://www.mail-archive.com/commits@nuttx.apache.org/>
+
+## Issue Tracker
+
+### Bug Reports:
+
+Found bug? Send an email to the dev list: <de...@nuttx.apache.org>
+
+Before submitting an issue, please:
+
+  - Verify that the bug does in fact exist. 
+  
+  - Search the mailing list archives to verify there is no existing issue
+    reporting the bug you've found.
+ 
+  - Consider tracking down the bug yourself in the NuttX source code and
+    submitting a patch along with your bug report.  This is a great time
+    saver for the NuttX developers and helps ensure the bug will be fixed
+    quickly.
+  
+### Feature Requests:
+  
+Enhancement requests for new features are also welcome. The more concrete
+and rational the request is, the greater the chance it will incorporated
+into future releases.
+
+## Source Code
+
+The project sources are in two Git repositories.  The core OS is in
+incubator-nuttx and the apps repository is in incubator-nuttx-apps.  These
+are housed in GitBox on ASF servers and also mirrored at GitHub.  These
+are kept in sync, so you can use whichever option you prefer.
+
+  - NuttX core OS repository:
+    
+    - Primary:
+      <https://gitbox.apache.org/repos/asf?p=incubator-nuttx.git>
+    
+    - GitHub Mirror:
+      <https://github.com/apache/incubator-nuttx>
+  
+  - Apps repository:
+    
+    - Primary:
+      <https://gitbox.apache.org/repos/asf?p=incubator-nuttx-apps.git>
+    
+    - GitHub Mirror:
+      <https://github.com/apache/incubator-nuttx-apps>
+
+## Website Source Code
+
+The project website sources are accessible via the website source code
+  repository which is also mirrored in GitHub:
+
+- Primary:
+  <https://gitbox.apache.org/repos/asf?p=incubator-nuttx-website.git>
+
+- GitHub Mirror:
+  <https://github.com/apache/incubator-nuttx-website>
+
+# ENVIRONMENTS
+
+  NuttX requires a POSIX development environment such as you would find under
+  Linux or macOS.  NuttX may also be installed and built on Windows system
+  if you also provide such a POSIX development environment.  Options for a
+  POSIX development environment under Windows include:
+
+  - An installation of Linux on a virtual machine (VM) in Windows.  I have
+    not been happy using a VM myself.  I have had stability problems with
+    open source VMs and commercial VMs cost more than I want to spend.
+    Sharing files with Linux running in a VM is awkward;  sharing devices
+    connected to the Windows box with Linux in a VM is, at the very least,
+    confusing;  Using Windows tools (such as Segger J-Link) with files
+    built under the Linux VM is not a possibility.
+
+  - The Cygwin environment.  Instructions for installation of Cygwin on a
+    Windows system are provided in the following paragraph, "Installing
+    Cygwin".  Cygwin is a mature, well-tested, and very convenient
+    environment.  It is especially convenient if you  need to
+    integrate with Windows tools and files.  Downsides are that the
+    installation time is very long and the compile times are slow.
+
+  - Ubuntu/Bash shell under Windows 10.  This is a new option under
+    Windows 10.  See the section "Ubuntu Bash under Windows 10" below.
+    This is an improvement over Cygwin if your concern is compile time;
+    its build performance is comparable to native Linux, certainly better
+    than the Cygwin build time.  It also installs in a tiny fraction of
+    the time as Cygwin, perhaps 20 minutes for the basic Ubuntu install
+    (vs. more than a day for the complete Cygwin install).
+  
+    There have been even more recent ports of Linux environment to
+    Windows.  I need to update this section to include some mention of
+    these alternatives.
+
+  - The MSYS environment.  MSYS derives from an older version of Cygwin
+    simplified and adapted to work more naturally in the Windows
+    environment.  See <http://www.mingw.org/wiki/MSYS> if you are
+    interested in using MSYS.  The advantages of the MSYS environment is
+    that it is better integrted with the native Windows environment and
+    lighter weight; it uses only a  minimal number of add-on POSIX-land
+    tools.
+  
+    The download link in that Wiki takes you to the SourceForge download
+    site.  The SourceForge MSYS project has been stagnant for some time.
+    The MSYS project has more recently moved to
+    <http://odsn.net/projects/sfnet_mingwbundle>.  Downloads of current .zip
+    files are available there but no instructions for the installation.
+
+  - MSYS2 appears to be a re-write of MSYS based on a newer version of
+    Cygwin.  Is it available at <https://www.msys2.org>.  A windows
+    installer is available at that site along with very good installation
+    instructions.  The download is relatively quick (at least compared to
+    Cygwin) and the 'pacman' package management tool supports supports
+    simple system updates.  For example, 'pacman -S git' will install the
+    GIT command line utilities.
+
+  - Other POSIX environments.  Check out:
+    
+    - UnxUtils: <https://sourceforge.net/projects/unxutils/>,
+      <https://en.wikipedia.org/wiki/UnxUtils>
+    - MobaXterm: <https://mobaxterm.mobatek.net/>
+    - Gow: <https://github.com/bmatzelle/gow/wiki>
+  
+    **Disclaimer**:  In principle, these should work.  However, I have never
+    used any of these environments and cannot guarantee that there is
+    not some less-than-obvious issues.
+  
+NuttX can also be installed and built on a native Windows system, but with
+some potential tool-related issues (see the discussion "Native Windows
+Build" under "Building NuttX" below).  GNUWin32 is used to provide
+compatible native windows tools.
+
+## Installing Cygwin
+
+Installing Cygwin on your Windows PC is simple, but time consuming.  See
+<http://www.cygwin.com/> for installation instructions. Basically you just
+need to download a tiny setup.exe program and it does the real, network
+installation for you.
+
+Some Cygwin installation tips:
+
+  1. Install at `C:\cygwin`
+  
+  2. Install **everything**:  "Only the minimal base packages from the
+     Cygwin distribution are installed by default. Clicking on categories
+     and packages in the setup.exe package installation screen will
+     provide you with the ability to control what is installed or updated.
+     Clicking on the "Default" field next to the "All" category will
+     provide you with the opportunity to install every Cygwin package.
+     Be advised that this will download and install hundreds of megabytes
+     to your computer."
+   
+If you use the "default" installation, you will be missing many
+of the Cygwin utilities that you will need to build NuttX.  The
+build will fail in numerous places because of missing packages.
+
+NOTE: The last time I installed **everything**, the download was
+about 5GiB.  The server I selected was also very slow so it took
+over a day to do the whole install!
+
+NOTE: You don't really have to install **everything** but I cannot
+answer the question "Then what should I install?"  I don't know
+the answer to that and so will continue to recommend installing
+**everything**.
+
+You should certainly be able to omit "Science", "Math", and
+"Publishing".  You can try omitting KDE, Gnome, GTK, and other
+graphics packages if you don't plan to use them.
+
+Perhaps a minimum set would be those packages listed below for the
+"Ubuntu Bash under Windows 10" installation?
+
+**UPDATE**:  Sergey Frolov had success with the following minimal
+Cygwin configuration:
+   
+   1. After starting the Cygwin installer, keep the recommended
+      packages that are pre-selected in the default configuration.
+   
+   2. Using the installation tools, add the following packages:
+      
+        make (GNU make)  bison        libgmp3-dev
+        gcc-core         byacc        libmpfr-dev
+        gcc-g++          gperf        libmpc-dev
+        flex             gdb          automake-1.15
+        libncurses-dev   libgmp-dev
+   
+After installing Cygwin, you will get lots of links for installed
+tools and shells.  I use the RXVT native shell.  It is fast and reliable
+and does not require you to run the Cygwin X server (which is neither
+fast nor reliable).  Unless otherwise noted, the rest of these
+instructions assume that you are at a bash command line prompt in
+either Linux or in Cygwin shell.
+
+## Using MSYS
+
+MSYS is an environment the derives from Cygwin.  Thus, most things said
+about Cygwin apply equally to MSYS.  This section will, then, focus on
+the differences when using MSYS, specifically MSYS2.
+
+Here is it assumed that you have already downloaded and installed MSYS2
+from https://www.msys2.org using the windows installer available at that
+location.  It is also assumed that you have brought in the necessary
+tools using the 'pacman' package management tool Tools needed including:
+
+  pacman -S git
+  pacman -S make
+  pacman -S gcc
+  pacman -S gdb
+
+And possibly others depending upon your usage.  Then you will need to
+build and install kconfig-frontends per the instructions of the top-level
+README.txt file in the tools repository.  This requires the following
+additional tools:
+
+    pacman -S bison
+    pacman -S gperf
+    pacman -S ncurses-devel
+    pacman -S automake-wrapper
+    pacman -S autoconf
+    pacman -S pkg-config
+
+Because of some versioning issues, I had to run 'aclocal' prior to
+running the kconfig-frontends configure script.  See "Configuring NuttX"
+below for further information.
+
+Unlike Cygwin, MSYS does not support symbolic links.  The 'ln -s' command
+will, in fact, copy a directory!  This means that you Make.defs file will
+have to include definitions like:
+
+    ifeq ($(CONFIG_WINDOWS_MSYS),y)
+      DIRLINK = $(TOPDIR)/tools/copydir.sh
+      DIRUNLINK = $(TOPDIR)/tools/unlink.sh
+    endif
+
+This will force the directory copies to work in a way that can be handled
+by the NuttX build system.  NOTE:  The default link.sh script has been
+updated so that is should now be MSYS2 compatible.  The above is preferred
+but no longer necessary in the Make.defs file.
+
+To build the simulator under MSYS, you also need:
+
+    pacman -S zlib-devel
+
+It appears that you cannot use directory names with spaces in them like
+"/c/Program\ Files \(86\)" in the MSYS path variable.  I worked around this
+by create Windows junctions like this:
+
+  1. Open the a windows command terminal,
+  
+  2. CD to `c:\msys64`, then
+  
+  3. `mklink /j programfiles "C:/Program\ Files"` and
+  
+  4. `mklink /j programfiles86 "C:/Program\ Files\ \(x86\)"`
+     
+     They then show up as `/programfiles` and `/programfiles86` with the MSYS2
+     sandbox.  Those paths can then be used with the PATH variable.  I had
+     to do something similar for the path to the GNU Tools "ARM Embedded
+     Toolchain" which also has spaces in the path name.
+
+## Ubuntu Bash under Windows 10
+
+A better version of a command-line only Ubuntu under Windows 10 (beta)
+has recently been made available from Microsoft.
+
+### Installation
+
+Installation instructions abound on the Internet complete with screen
+shots.  I will attempt to duplicate those instructions in full here.
+Here are the simplified installation steps:
+
+  - Open *Settings*.
+  
+  - Click on *Update & security*.
+  
+  - Click on *For Developers*.
+  
+  - Under *Use developer features*, select the *Developer mode* option to
+    setup the environment to install Bash.
+  
+  - A message box should pop up.  Click *Yes* to turn on developer mode.
+  
+  - After the necessary components install, you'll need to restart your
+    computer.
+    
+    Once your computer reboots:
+  
+  - Open *Control Panel*.
+  
+  - Click on *Programs*.
+  
+  - Click on *Turn Windows features on or off*.
+  
+  - A list of features will pop up, check the *Windows Subsystem for Linux
+    (beta)* option.
+  
+  - Click *OK*.
+  
+  - Once the components installed on your computer, click the *Restart
+    now* button to complete the task.
+    
+    After your computer restarts, you will notice that Bash will not appear in
+    the *Recently added* list of apps, this is because Bash isn't actually
+    installed yet. Now that you have setup the necessary components, use the
+    following steps to complete the installation of Bash:
+  
+  - Open *Start*, do a search for `bash.exe`, and press *Enter*.
+  
+  - On the command prompt, type `y` and press Enter to download and install
+    Bash from the Windows Store.  This will take awhile.
+  
+  - Then you'll need to create a default UNIX user account. This account
+    doesn't have to be the same as your Windows account. Enter the
+    username in the required field and press Enter (you can't use the
+    username `admin`).
+  
+  - Close the `bash.exe` command prompt.
+  
+  Now that you completed the installation and setup, you can open the Bash
+  tool from the Start menu like you would with any other app.
+
+### Accessing Windows Files from Ubuntu
+
+File systems will be mounted under `/mnt` so for example `C:\Program Files`
+appears at `/mnt/c/Program Files`.  This is as opposed to Cygwin where
+the same directory would appear at `/cygdrive/c/Program Files`.
+
+With these differences (perhaps a few other Windows quirks) the Ubuntu
+install works just like Ubuntu running natively on your PC.
+
+A good tip for file sharing is to use symbolic links within your Ubuntu
+home directory.  For example, suppose you have your `projects` directory
+at `C:\Documents\projects`.  Then you can set up a link to the `projects/`
+directory in your Ubuntu directory like:
+
+    ln -s /mnt/c/Documents/projects projects
+
+### Accessing Ubuntu Files From Windows
+
+In Ubuntu Userspace for Windows, the Ubuntu file system root directory is
+at:
+
+    %localappdata%\lxss\rootfs
+
+Or
+
+    C:\Users\Username\AppData\Local\lxss\rootfs
+
+However, I am unable to see my files under the rootfs\home directory.
+After some looking around, I find the home directory
+`%localappdata%\lxss\home`.
+
+With that trick access to the `/home` directory, you should actually be
+able to use Windows tools outside of the Ubuntu sandbox with versions of
+NuttX built within the sandbox using that path.
+
+### Executing Windows Tools from Ubuntu
+
+You can also execute Windows tools from within the Ubuntu sandbox:
+
+    /mnt/c/Program\ Files\ \(x86\)/Microchip/xc32/v1.43/bin/xc32-gcc.exe --version
+    Unable to translate current working directory. Using C:\WINDOWS\System32
+    xc32-gcc.exe (Microchip Technology) 4.8.3 MPLAB XC32 Compiler v1.43 Build date: Mar  1 2017
+    ...
+
+The error message indicates that there are more issues:  You cannot mix
+Windows tools that use Windows style paths in an environment that uses
+POSIX paths.  I think you would have to use Linux tools only from within
+the Ubuntu sandbox.
+
+### Install Ubuntu Software
+
+Use `sudo apt-get install <package name>`.  As examples, this is how
+you would get GIT:
+
+    sudo apt-get install git
+
+This will get you a compiler for your host PC:
+
+    sudo apt-get install gcc
+
+This will get you an ARM compiler for your target:
+
+    sudo apt-get install gcc-arm-none-eabi
+
+**NOTE**: That is just an example.  I am not sure if apt-get will give you a
+current or usable compiler.  You should carefully select your toolchain
+for the needs of your project.
+
+You will also need to get the kconfig-frontends configuration as
+described below under *NuttX Configuration Tool*.  In order to build the
+kconfig-frontends configuration tool you will also need: `make`, `gperf`,
+`flex`, `bison`, and `libncurses-dev`.
+
+That is enough to do a basic NuttX build.
+
+### Integrating with Windows Tools
+
+If you want to integrate with Windows native tools, then you would need
+deal with the same kind of craziness as with integrating Cygwin with
+native toolchains, see the section *Cygwin Build Problems* below.
+
+However, there is currently no build support for using Windows native
+tools with Ubuntu under Windows.  This tool combination is made to work
+with Cygwin through the use of the `cygpath -w` tool that converts paths
+from say `/cydrive/c/Program Files` to `C:\Program Files`.  There is,
+however, no corresponding tool to convert `/mnt/c/Program Files` in the
+Ubuntu environment.
+
+### Graphics Support
+
+The Ubuntu version support by Microsoft is a command-line only version.
+There is no support for Linux graphics utilities.
+
+This limitation is not a limitation of Ubuntu, however, only in what
+Microsoft is willing to support.  If you install a X-Server, then you
+can also use basic graphics utilities.  See for example:
+
+  <http://www.howtogeek.com/261575/how-to-run-graphical-linux-desktop-applications-from-windows-10s-bash-shell/>
+
+Many Linux graphics programs would, however, also require a graphics
+framework like GTK or Qt.  So this might be a trip down the rabbit hole.
+
+### Using macOS
+
+You need to install at least the following tools specific to macOS.
+
+  * flock (used by APPDIR build logic)
+    
+A macOS port is available at: <https://github.com/discoteq/flock>
+  
+    brew tap discoteq/discoteq
+    brew install flock
+  
+  If you want to build the sim:
+
+  * Xcode (the native compiler and the rest of the toolchain)
+
+  * ELF toolchain (if you want to build modules for CONFIG_LIBC_MODLIB)
+
+    brew install x86_64-elf-gc
+
+# INSTALLATION
+
+There are two ways to get NuttX:  You may download released, stable
+tarballs from either the project website.  Or you may get NuttX by
+cloning the GIT repositories.  Let's consider the released tarballs
+first:
+
+## Download and Unpack
+
+Download and unpack the NuttX tarball.  If you are reading this, then
+you have probably already done that.  After unpacking, you will end
+up with a directory called nuttx-version (where version is the NuttX
+version number). You might want to rename that directory nuttx to
+match the various instructions in the documentation and some scripts
+in the source tree.
+
+  * Download location:
+  
+    <https://nuttx.apache.org/download/>
+  
+  * Legacy download locations:
+
+    <https://bitbucket.org/nuttx/nuttx/downloads>  
+    <https://sourceforge.net/projects/nuttx/files/nuttx/>
+
+## Semi-Optional apps/ Package
+
+All NuttX libraries and example code used to be in included within
+the NuttX source tree.  As of NuttX-6.0, this application code was
+moved into a separate tarball, the apps tarball.  If you are just
+beginning with NuttX, then you will want to download the versioned
+apps tarball along with the NuttX tarball.  If you already have your
+own product application directory, then you may not need the apps
+tarball.
+
+It is called "Semi-optional" because if you don't have some `apps/`
+directory, NuttX will *fail* to build! You do not necessarily need
+to use the NuttX apps tarball but may, instead, provide your own
+custom application directory.  Such a custom directory would need
+to include a valid Makefile to support the build and a valid Kconfig
+file to support the configuration.  More about these files later.
+
+Download then unpack the apps tarball in the same directory where you
+unpacked the NuttX tarball.  After you unpack the apps tarball, you
+will have a new directory called apps-version (where the version
+should exactly match the version of the NuttX tarball).  Again, you
+might want to rename the directory to simply apps/ to match what
+you read in the documentation
+
+After unpacking (and renaming) the apps tarball, you will have two
+directories side by side like this:
+
+             |
+        +----+----+
+        |         |
+      nuttx/     apps/
+
+This is important because the NuttX build will expect to find the
+apps directory in that (default) location.  That default location
+can be changed by modifying your NuttX configuration file, but that
+is another story.
+
+## Installation Directories with Spaces in the Path
+
+The nuttx build directory should reside in a path that contains no
+spaces in any higher level directory name.  For example, under
+Cygwin, your home directory might be formed from your first and last
+names like: `/home/First Last`. That will cause strange errors when
+the make system tries to build.
+
+[Actually, that problem is probably not too difficult to fix.  Some
+ Makefiles probably just need some paths within double quotes]
+
+I work around spaces in the home directory name, by creating a
+new directory that does not contain any spaces, such as `/home/nuttx`.
+Then I install NuttX in `/home/nuttx` and always build from
+`/home/nuttx/nuttx-code`.
+
+## Downloading from Repositories
+
+### Cloning the Repository
+
+**BEFORE** cloning repositories on any Windows platform do the following GIT
+command:
+
+    git config --global core.autocrlf false
+
+That will avoid conversions of linefeeds (newlines, \n) to carriage
+return plus linefeed sequences (\r\n)
+
+The current NuttX du jour is available in from a GIT repository.  Here are
+instructions for cloning the core NuttX RTOS (corresponding to the nuttx
+tarball discussed above):
+
+    git clone https://gitbox.apache.org/repos/asf/incubator-nuttx.git nuttx
+
+-or-
+
+    git clone https://github.com/apache/incubator-nuttx.git nuttx
+
+And the semi-optional apps/ application directory and be cloned like:
+
+    git clone https://gitbox.apache.org/repos/asf/incubator-nuttx-apps.git apps
+  
+-or-
+  
+    git clone https://github.com/apache/incubator-nuttx-apps.git apps
+
+That will give you the same directory structure like this:
+    
+             |
+        +----+----+
+        |         |
+      nuttx/     apps/
+
+### Configuring the Clones
+
+The following steps need to be performed for each of the repositories.
+After changing to the clone directory:
+
+Set your identity:
+
+    git config --global user.name "My Name"
+    git config --global user.email my.name@example.com
+  
+Colorized diffs are much easier to read:
+
+    git config --global color.branch auto
+    git config --global color.diff auto
+    git config --global color.interactive auto
+    git config --global color.status auto
+
+Checkout other settings
+
+    git config --list
+
+### Cloning NuttX Inside Cygwin
+
+If you are cloning the NuttX repository, it is recommended to avoid
+automatic end of lines conversions by git. These conversions may break
+some scripts like configure.sh. Before cloning, do the following:
+
+    git config --global core.autocrlf false
+
+## Related Repositories
+
+These are standalone repositories:
+
+  * <https://gitbox.apache.org/repos/asf/incubator-nuttx-apps>  
+    or  
+    <https://github.com/apache/incubator-nuttx-apps.git>
+    
+    This directory holds an optional package of applications and libraries
+    can be used with the NuttX RTOS.  There is a README.txt file there that
+    will provide more information about that package.
+
+  * <https://bitbucket.org/nuttx/nxwidgets>
+  
+    This is the NuttX C++ graphics support.  This includes NxWM, the tiny
+    NuttX Window Manager.
+
+  * <https://bitbucket.org/nuttx/uclibc>
+  
+    This repository contains a version of the uClibc++ C++ library.  This code
+    originates from <http://cxx.uclibc.org/> and has been adapted for NuttX by the
+    RGMP team (<http://rgmp.sourceforge.net/wiki/index.php/Main_Page>).
+
+  * <https://bitbucket.org/nuttx/buildroot>
+  
+    A environment that you can to use to build a custom, NuttX GNU toolchain.
+
+  * <https://bitbucket.org/nuttx/tools>
+  
+    There are snapshots of some tools here that you will need to work with
+    NuttX:  kconfig-frontends, genromfs, and others.
+
+## Notes about Header Files
+
+### Other C-Library Header Files
+
+When a GCC toolchain is built, it must be built against a C library.
+The compiler together with the contents of the C library completes the
+C language definition and provides the complete C development
+environment.  NuttX provides its own, built-in C library.  So the
+complete, consistent C language definition for use with NuttX comes from
+the combination of the compiler and the header files provided by the
+NuttX C library.
+
+When a GCC toolchain is built, it incorporates the C library header
+files into the compiler internal directories and, in this way, the C
+library really becomes a part of the toolchain.  If you use the NuttX
+buildroot toolchain as described below under "NuttX Buildroot
+Toolchain", your GCC toolchain will build against the NuttX C library
+and will incorporate the NuttX C library header files as part of the
+toolchain.
+
+If you use some other, third-party tool chain, this will not be the
+case, however.  Those toolchains were probably built against some
+other, incompatible C library distribution (such as newlib).  Those
+tools will have incorporated the incompatible C library header files
+as part of the toolchain.  These incompatible header files must *not*
+be used with NuttX because they will conflict with definitions in the
+NuttX built-in C-Library.  For such toolchains that include header
+files from a foreign C-Library, NuttX must be compiled without using
+the standard header files that are distributed with your toolchain.
+This prevents including conflicting, incompatible header files such
+as stdio.h.
+
+The math.h and stdarg.h are probably the two most trouble some header
+files to deal with.  These troublesome header files are discussed in
+more detail below.
+
+### Header Files Provided by Your Toolchain
+
+Certain header files, such as `setjmp.h`, `stdarg.h`, and `math.h`, may still
+be needed from your toolchain and your compiler may not, however, be able
+to find these if you compile NuttX without using standard header files
+(i.e., with `-nostdinc`).  If that is the case, one solution is to copy
+those header file from your toolchain into the NuttX include directory.
+
+### Duplicated Header Files
+
+There are also a few header files that can be found in the `nuttx/include`
+directory which are duplicated by the header files from your toolchain.
+stdint.h and stdbool.h are examples.  If you prefer to use the `stdint.h`
+and `stdbool.h` header files from your toolchain, those could be copied
+into the `nuttx/include/` directory. Using most other header files from
+your toolchain would probably cause errors.
+
+### math.h
+
+Even though you should not use a foreign C-Library, you may still need
+to use other, external libraries with NuttX.  In particular, you may
+need to use the math library, libm.a.  NuttX supports a generic, built-in
+math library that can be enabled using `CONFIG_LIBM=y`.  However, you may
+still want to use a higher performance external math library that has
+been tuned for your CPU.  Sometimes such tuned math libraries are
+bundled with your toolchain.
+
+The math library header file, `math.h`, is a then special case.  If you do
+nothing, the standard math.h header file that is provided with your
+toolchain will be used.
+
+If you have a custom, architecture specific math.h header file, then
+that header file should be placed at `arch/<cpu>/include/math.h`.  There
+is a stub `math.h` header file located at `include/nuttx/lib/math.h`.  This stub
+header file can be used to "redirect" the inclusion to an architecture-
+specific math.h header file.  If you add an architecture specific math.h
+header file then you should also define `CONFIG_ARCH_MATH_H=y` in your
+NuttX Configuration file.  If `CONFIG_ARCH_MATH_H` is selected, then the
+top-level Makefile will copy the stub math.h header file from
+`include/nuttx/lib/math.h` to `include/math.h` where it will become the system
+`math.h` header file.  The stub `math.h` header file does nothing other
+than to include that architecture-specific `math.h` header file as the
+system `math.h` header file.
+
+### float.h
+
+If you enable the generic, built-in math library, then that math library
+will expect your toolchain to provide the standard `float.h` header file.
+The float.h header file defines the properties of your floating point
+implementation.  It would always be best to use your toolchain's `float.h`
+header file but if none is available, a default `float.h` header file will
+be provided if this option is selected.  However, there is no assurance
+that the settings in this `float.h` are actually correct for your platform!
+
+### stdarg.h
+
+In most cases, the correct version of stdarg.h is the version provided
+with your toolchain.  However, sometimes there are issues with
+using your toolchains `stdarg.h`.  For example, it may attempt to draw in
+header files that do not exist in NuttX or perhaps the header files that
+it uses are not compatible with the NuttX header files.  In those cases,
+you can use an architecture-specific `stdarg.h` header file by defining
+`CONFIG_ARCH_STDARG_H=y`.
+
+See the discussion above for the `math.h` header.  This setting works
+exactly the same for the `stdarg.h` header file.
+
+# CONFIGURING NUTTX
+
+## Instantiating "Canned" Configurations
+
+### `configure.sh` and `configure.bat`
+
+"Canned" NuttX configuration files are retained in:
+
+    boards/<arch-name>/<chip-name>/<board-name>/configs/<config-dir>
+
+Where `<board-name>` is the name of your development board and `<config-dir>`
+is the name of the sub-directory containing a specific configuration for
+that board. `<arch-name>` and `<chip-name>` refer to characteristics of the
+MCU used on the board: `<arch-name>` is the CPU architecture implemented
+by the MCU; `<chip-name>` identifies the MCU chip family.  Only a few
+steps are required to instantiate a NuttX configuration, but to make the
+configuration even easier there are scripts available in the tools/
+sub-directory combines those simple steps into one command.
+
+There is one tool for use with any Bash-like shell that does configuration
+steps.  It is used as follows:
+
+    tools/configure.sh <board-name>:<config-dir>
+
+There is an alternative Windows batch file that can be used in the windows
+native environment like:
+
+    tools\configure.bat <board-name>:<config-dir>
+
+And, to make sure that other platforms are supported, there is also a
+C program at tools/configure.c that can be compiled to establish the
+board configuration.
+
+See `tools/README.txt` for more information about these scripts.
+
+General information about configuring NuttX can be found in:
+
+    {TOPDIR}/boards/README.txt
+    {TOPDIR}/boards/<arch-name>/<chip-name>/<board-name>/README.txt
+
+### The Hidden Configuration Scripts:
+
+As mentioned above, there are only a few simple steps to instantiating a
+NuttX configuration.  Those steps are hidden by the configuration scripts
+but are summarized below:
+  
+  1. Copy Files
+  
+     Configuring NuttX requires only copying two files from the
+     `<config-dir>` to the directory where you installed NuttX (TOPDIR):
+  
+       * Copy `boards/<arch-name>/<chip-name>/<board-name>/configs/<config-dir>/Make.def` to `{TOPDIR}/Make.defs`
+    
+         OR
+    
+       * Copy `boards/<arch-name>/<chip-name>/<board-name>/scripts/Make.def`
+         to `{TOPDIR}/Make.defs`
+    
+         Make.defs describes the rules needed by your tool chain to compile
+         and link code.  You may need to modify this file to match the
+         specific needs of your toolchain.  NOTE that a configuration may
+         have its own unique Make.defs file in its configuration directory or
+         it may use a common Make.defs file for the board in the scripts/
+         directory.  The first takes precedence.
+    
+       * Copy `boards/<arch-name>/<chip-name>/<board-name>/configs/<config-dir>/defconfig` to `{TOPDIR}/.config`
+    
+         The defconfig file holds the actual build configuration.  This
+         file is included by all other make files to determine what is
+         included in the build and what is not.  This file is also used
+         to generate a C configuration header at `include/nuttx/config.h`.
+    
+       * Copy other, environment-specific files to `{TOPDIR}`
+    
+         This might include files like .gdbinit or IDE configuration files
+         like .project or .cproject.
+  
+  2. Refresh the Configuration
+  
+     New configuration setting may be added or removed.  Existing settings
+     may also change there values or options.  This must be handled by
+     refreshing the configuration as described below.
+    
+     NOTE:  NuttX uses only compressed defconfig files.  For the NuttX
+     defconfig files, this refreshing step is *NOT* optional; it is also
+     necessary to uncompress and regenerate the full making file.  This is
+     discussed further below.
+
+## Refreshing Configurations
+
+Configurations can get out of date.  As new configuration settings are
+added or removed or as dependencies between configuration settings
+change, the contents of a default configuration can become out of synch
+with the build systems.  Hence, it is a good practice to "refresh" each
+configuration after configuring and before making.  To refresh the
+configuration, use the NuttX Configuration Tool like this:
+
+    make oldconfig
+
+AFTER you have instantiated the NuttX configuration as described above.
+The configuration step copied the .config file into place in the top-level
+NuttX directory; 'make oldconfig' step will then operate on that .config
+file to bring it up-to-date.
+
+If your configuration is out of date, you will be prompted by 'make oldconfig'
+to resolve the issues detected by the configuration tool, that is, to
+provide values for the new configuration options in the build system.  Doing
+this can save you a lot of problems down the road due to obsolete settings in
+the default board configuration file.  The NuttX configuration tool is
+discussed in more detail in the following paragraph.
+
+Confused about what the correct value for a new configuration item should
+be?  Enter ? in response to the 'make oldconfig' prompt and it will show
+you the help text that goes with the option.
+
+If you don't want to make any decisions are willing to just accept the
+recommended default value for each new configuration item, an even easier
+way is:
+
+    make olddefconfig
+
+The olddefconfig target will simply bring your configuration up to date with
+the current Kconfig files, setting any new options to the default value.
+No questions asked.
+
+## NuttX Configuration Tool
+
+An automated tool has been incorporated to support re-configuration
+of NuttX.  This tool is based on the kconfig-frontends application available
+at <https://bitbucket.org/nuttx/tools/src/master/kconfig-frontends/>.  (This
+is a snapshot of the old <http://ymorin.is-a-geek.org/projects/kconfig-frontends>
+which is no longer available.)  This application provides a tool called
+`kconfig-mconf` that is used by the NuttX top-level Makefile. The following
+make target is provided:
+
+    make menuconfig
+
+This make target will bring up NuttX configuration menus.
+
+**WARNING**:  Never do `make menuconfig` on a configuration that has
+not been converted to use the kconfig-frontends tools!  This will
+damage your configuration (see
+<http://www.nuttx.org/doku.php?id=wiki:howtos:convertconfig>).
+
+How do we tell a new configuration from an old one? See "Incompatibilities
+with Older Configurations" below.
+
+The `menuconfig` make target depends on two things:
+
+  1. The Kconfig configuration data files that appear in almost all
+     NuttX directories.  These data files are the part that is still
+     under development (patches are welcome!).  The Kconfig files
+     contain configuration information for the configuration settings
+     relevant to the directory in which the Kconfig file resides.
+     
+     NOTE: For a description of the syntax of this configuration file,
+     see kconfig-language.txt in the tools repository at
+     <https://bitbucket.org/nuttx/tools>
+  
+  2. The `kconfig-mconf` tool. `kconfig-mconf` is part of the
+     kconfig-frontends package.  You can download that package from the
+     snapshot in the tools repository at <https://bitbucket.org/nuttx/tools>.
+  
+     Building kconfig-frontends under Linux may be as simple as
+     `configure; make; make install` but there may be some build
+     complexities, especially if you are building under Cygwin.  See
+     the more detailed build instructions in the top-level README.txt
+     file of the tools repository at <https://bitbucket.org/nuttx/tools>.
+  
+  
+     The `make install` step will, by default, install the `kconfig-mconf`
+     tool at `/usr/local/bin/mconf`.  Where ever you choose to
+     install `kconfig-mconf`, make certain that your PATH variable includes
+     a path to that installation directory.
+  
+     The kconfig-frontends tools will not build in a native Windows
+     environment directly "out-of-the-box".  For the Windows native
+     case, you can use the modified version of kconfig-frontends
+     that can be found at
+
+     <http://uvc.de/posts/linux-kernel-configuration-tool-kconfig-under-windows.html>  
+
+     or a more recent port that can be found at  
+
+     <http://reclonelabs.com/more-kconfig-awesomeness-for-windows/>.
+   
+The basic configuration order is "bottom-up":
+   
+   - Select the build environment,
+   - Select the processor,
+   - Select the board,
+   - Select the supported peripherals
+   - Configure the device drivers,
+   - Configure the application options on top of this.
+   
+This is pretty straight forward for creating new configurations
+but may be less intuitive for modifying existing configurations.
+
+Another ncurses-based tool that is an option to kconfig-mconf is
+kconfig-nconf.  The differences are primary in in the aesthetics of the
+UI.  If you have kconfig-nconf built, then you can invoke that front end
+with:
+   
+     make nconfig
+   
+If you have an environment that supports the Qt or GTK graphical systems
+(probably KDE or gnome, respectively, or Cygwin under Windows with Qt or
+GTK installed), then you can also build the graphical kconfig-frontends,
+kconfig-qconf and kconfig-gconf.  In these case, you can start the
+graphical configurator with either:
+   
+     make qconfig
+   
+ or
+   
+     make gconfig
+   
+Some keyboard shortcuts supported by kconfig-mconf, the tool that runs
+when you do 'make menuconfig':
+
+   - `?` will bring up the mconfig help display.
+   
+   - `/` can be used find configuration selections.
+   
+   - `Z` can be used to reveal hidden configuration options
+   
+These last two shortcuts are described further in the following
+paragraphs.
+
+## Finding Selections in the Configuration Menus
+
+The NuttX configuration options have gotten complex and it can be very
+difficult to find options in the menu trees if you are not sure where
+to look.  The "basic configuration order" describe above can help to
+narrow things down.
+
+But if you know exactly what configuration setting you want to select,
+say CONFIG_XYZ, but not where to find it, then the 'make menuconfig'

Review comment:
       @v01d Could you use backticks around `CONFIG_XYZ` to make it preformatted, since it's a config variable?

##########
File path: README.md
##########
@@ -0,0 +1,2513 @@
+# APACHE NUTTX (INCUBATING)
+
+* Introduction
+  - Incubation Status
+* Community
+  - Getting Help
+  - Mailing Lists
+  - Issue Tracker
+  - Source Code
+  - Website Source Code
+* Environments
+  - Installing Cygwin
+  - Ubuntu Bash under Windows 10
+  - Using macOS
+* Installation
+  - Download and Unpack
+  - Semi-Optional apps/ Package
+  - Installation Directories with Spaces in the Path
+  - Downloading from Repositories
+  - Related Repositories
+  - Notes about Header Files
+* Configuring NuttX
+  - Instantiating "Canned" Configurations
+  - Refreshing Configurations
+  - NuttX Configuration Tool
+  - Finding Selections in the Configuration Menus
+  - Reveal Hidden Configuration Options
+  - Make Sure that You are on the Right Platform
+  - Comparing Two Configurations
+  - Making defconfig Files
+  - Incompatibilities with Older Configurations
+  - NuttX Configuration Tool under DOS
+* Toolchains
+  - Cross-Development Toolchains
+  - NuttX Buildroot Toolchain
+* Shells
+* Building NuttX
+  - Building
+  - Re-building
+  - Build Targets and Options
+  - Native Windows Build
+  - Installing GNUWin32
+* Cygwin Build Problems
+  - Strange Path Problems
+  - Window Native Toolchain Issues
+* Documentation
+
+# INTRODUCTION
+
+Apache NuttX (Incubating) is a real-time operating system (RTOS) with an
+emphasis on standards compliance and small footprint.  Scalable from 8-bit
+to 32-bit microcontroller environments, the primary governing standards in
+NuttX are POSIX and ANSI standards. Additional standard APIs from Unix and
+other common RTOSs (such as VxWorks) are adopted for functionality not
+available under these standards, or for functionality that is not
+appropriate for deeply-embedded environments (such as fork()).
+
+Extensive documentation can be found on the project wiki:
+  <https://cwiki.apache.org/NUTTX/Nuttx>
+
+## Incubation Status
+
+Apache NuttX (Incubating) is an effort undergoing Incubation at The Apache
+Software Foundation (ASF), sponsored by the Incubator.  For more on our
+incubation effort, please see the file DISCLAIMER-WIP, in the same
+directory as this README.
+
+For brevity, the rest of this file will refer to it as Apache NuttX or
+simply NuttX.
+
+# COMMUNITY
+
+Every volunteer project obtains its strength from the people involved in
+it.  We invite you to participate as much or as little as you choose.
+
+We encourage you to:
+
+  - Use our project and provide feedback.
+  - Provide us with use-cases.
+  - Report bugs and submit patches.
+  - Contribute code or documentation.
+
+## Getting Help
+
+The best place to get help is the developer's mailing list.  Please see
+the following section:
+
+## Mailing Lists
+
+Get help using NuttX or contribute to the project on our mailing lists:
+
+  * <de...@nuttx.apache.org> is for people who want to contribute code to NuttX.
+    * To subscribe, send an email to <de...@nuttx.apache.org>.
+    * To unsubscribe, send an email to <de...@nuttx.apache.org>.
+    * View the archives at:
+      <https://www.mail-archive.com/dev@nuttx.apache.org/>
+
+  * <co...@nuttx.apache.org> is a read-only list that notifies subscribers
+  about commit messages and patches to NuttX.
+    * To subscribe, send an email to <co...@nuttx.apache.org>.
+    * To unsubscribe, send an email to <co...@nuttx.apache.org>.
+    * View the archives at:
+      <https://www.mail-archive.com/commits@nuttx.apache.org/>
+
+## Issue Tracker
+
+### Bug Reports:
+
+Found bug? Send an email to the dev list: <de...@nuttx.apache.org>
+
+Before submitting an issue, please:
+
+  - Verify that the bug does in fact exist. 
+  
+  - Search the mailing list archives to verify there is no existing issue
+    reporting the bug you've found.
+ 
+  - Consider tracking down the bug yourself in the NuttX source code and
+    submitting a patch along with your bug report.  This is a great time
+    saver for the NuttX developers and helps ensure the bug will be fixed
+    quickly.
+  
+### Feature Requests:
+  
+Enhancement requests for new features are also welcome. The more concrete
+and rational the request is, the greater the chance it will incorporated
+into future releases.
+
+## Source Code
+
+The project sources are in two Git repositories.  The core OS is in
+incubator-nuttx and the apps repository is in incubator-nuttx-apps.  These
+are housed in GitBox on ASF servers and also mirrored at GitHub.  These
+are kept in sync, so you can use whichever option you prefer.
+
+  - NuttX core OS repository:
+    
+    - Primary:
+      <https://gitbox.apache.org/repos/asf?p=incubator-nuttx.git>
+    
+    - GitHub Mirror:
+      <https://github.com/apache/incubator-nuttx>
+  
+  - Apps repository:
+    
+    - Primary:
+      <https://gitbox.apache.org/repos/asf?p=incubator-nuttx-apps.git>
+    
+    - GitHub Mirror:
+      <https://github.com/apache/incubator-nuttx-apps>
+
+## Website Source Code
+
+The project website sources are accessible via the website source code
+  repository which is also mirrored in GitHub:
+
+- Primary:
+  <https://gitbox.apache.org/repos/asf?p=incubator-nuttx-website.git>
+
+- GitHub Mirror:
+  <https://github.com/apache/incubator-nuttx-website>
+
+# ENVIRONMENTS
+
+  NuttX requires a POSIX development environment such as you would find under
+  Linux or macOS.  NuttX may also be installed and built on Windows system
+  if you also provide such a POSIX development environment.  Options for a
+  POSIX development environment under Windows include:
+
+  - An installation of Linux on a virtual machine (VM) in Windows.  I have
+    not been happy using a VM myself.  I have had stability problems with
+    open source VMs and commercial VMs cost more than I want to spend.
+    Sharing files with Linux running in a VM is awkward;  sharing devices
+    connected to the Windows box with Linux in a VM is, at the very least,
+    confusing;  Using Windows tools (such as Segger J-Link) with files
+    built under the Linux VM is not a possibility.
+
+  - The Cygwin environment.  Instructions for installation of Cygwin on a
+    Windows system are provided in the following paragraph, "Installing
+    Cygwin".  Cygwin is a mature, well-tested, and very convenient
+    environment.  It is especially convenient if you  need to
+    integrate with Windows tools and files.  Downsides are that the
+    installation time is very long and the compile times are slow.
+
+  - Ubuntu/Bash shell under Windows 10.  This is a new option under
+    Windows 10.  See the section "Ubuntu Bash under Windows 10" below.
+    This is an improvement over Cygwin if your concern is compile time;
+    its build performance is comparable to native Linux, certainly better
+    than the Cygwin build time.  It also installs in a tiny fraction of
+    the time as Cygwin, perhaps 20 minutes for the basic Ubuntu install
+    (vs. more than a day for the complete Cygwin install).
+  
+    There have been even more recent ports of Linux environment to
+    Windows.  I need to update this section to include some mention of
+    these alternatives.
+
+  - The MSYS environment.  MSYS derives from an older version of Cygwin
+    simplified and adapted to work more naturally in the Windows
+    environment.  See <http://www.mingw.org/wiki/MSYS> if you are
+    interested in using MSYS.  The advantages of the MSYS environment is
+    that it is better integrted with the native Windows environment and
+    lighter weight; it uses only a  minimal number of add-on POSIX-land
+    tools.
+  
+    The download link in that Wiki takes you to the SourceForge download
+    site.  The SourceForge MSYS project has been stagnant for some time.
+    The MSYS project has more recently moved to
+    <http://odsn.net/projects/sfnet_mingwbundle>.  Downloads of current .zip
+    files are available there but no instructions for the installation.
+
+  - MSYS2 appears to be a re-write of MSYS based on a newer version of
+    Cygwin.  Is it available at <https://www.msys2.org>.  A windows
+    installer is available at that site along with very good installation
+    instructions.  The download is relatively quick (at least compared to
+    Cygwin) and the 'pacman' package management tool supports supports
+    simple system updates.  For example, 'pacman -S git' will install the
+    GIT command line utilities.
+
+  - Other POSIX environments.  Check out:
+    
+    - UnxUtils: <https://sourceforge.net/projects/unxutils/>,
+      <https://en.wikipedia.org/wiki/UnxUtils>
+    - MobaXterm: <https://mobaxterm.mobatek.net/>
+    - Gow: <https://github.com/bmatzelle/gow/wiki>
+  
+    **Disclaimer**:  In principle, these should work.  However, I have never
+    used any of these environments and cannot guarantee that there is
+    not some less-than-obvious issues.
+  
+NuttX can also be installed and built on a native Windows system, but with
+some potential tool-related issues (see the discussion "Native Windows
+Build" under "Building NuttX" below).  GNUWin32 is used to provide
+compatible native windows tools.
+
+## Installing Cygwin
+
+Installing Cygwin on your Windows PC is simple, but time consuming.  See
+<http://www.cygwin.com/> for installation instructions. Basically you just
+need to download a tiny setup.exe program and it does the real, network
+installation for you.
+
+Some Cygwin installation tips:
+
+  1. Install at `C:\cygwin`
+  
+  2. Install **everything**:  "Only the minimal base packages from the
+     Cygwin distribution are installed by default. Clicking on categories
+     and packages in the setup.exe package installation screen will
+     provide you with the ability to control what is installed or updated.
+     Clicking on the "Default" field next to the "All" category will
+     provide you with the opportunity to install every Cygwin package.
+     Be advised that this will download and install hundreds of megabytes
+     to your computer."
+   
+If you use the "default" installation, you will be missing many
+of the Cygwin utilities that you will need to build NuttX.  The
+build will fail in numerous places because of missing packages.
+
+NOTE: The last time I installed **everything**, the download was
+about 5GiB.  The server I selected was also very slow so it took
+over a day to do the whole install!
+
+NOTE: You don't really have to install **everything** but I cannot
+answer the question "Then what should I install?"  I don't know
+the answer to that and so will continue to recommend installing
+**everything**.
+
+You should certainly be able to omit "Science", "Math", and
+"Publishing".  You can try omitting KDE, Gnome, GTK, and other
+graphics packages if you don't plan to use them.
+
+Perhaps a minimum set would be those packages listed below for the
+"Ubuntu Bash under Windows 10" installation?
+
+**UPDATE**:  Sergey Frolov had success with the following minimal
+Cygwin configuration:
+   
+   1. After starting the Cygwin installer, keep the recommended
+      packages that are pre-selected in the default configuration.
+   
+   2. Using the installation tools, add the following packages:
+      
+        make (GNU make)  bison        libgmp3-dev
+        gcc-core         byacc        libmpfr-dev
+        gcc-g++          gperf        libmpc-dev
+        flex             gdb          automake-1.15
+        libncurses-dev   libgmp-dev
+   
+After installing Cygwin, you will get lots of links for installed
+tools and shells.  I use the RXVT native shell.  It is fast and reliable
+and does not require you to run the Cygwin X server (which is neither
+fast nor reliable).  Unless otherwise noted, the rest of these
+instructions assume that you are at a bash command line prompt in
+either Linux or in Cygwin shell.
+
+## Using MSYS
+
+MSYS is an environment the derives from Cygwin.  Thus, most things said
+about Cygwin apply equally to MSYS.  This section will, then, focus on
+the differences when using MSYS, specifically MSYS2.
+
+Here is it assumed that you have already downloaded and installed MSYS2
+from https://www.msys2.org using the windows installer available at that
+location.  It is also assumed that you have brought in the necessary
+tools using the 'pacman' package management tool Tools needed including:
+
+  pacman -S git
+  pacman -S make
+  pacman -S gcc
+  pacman -S gdb
+
+And possibly others depending upon your usage.  Then you will need to
+build and install kconfig-frontends per the instructions of the top-level
+README.txt file in the tools repository.  This requires the following
+additional tools:
+
+    pacman -S bison
+    pacman -S gperf
+    pacman -S ncurses-devel
+    pacman -S automake-wrapper
+    pacman -S autoconf
+    pacman -S pkg-config
+
+Because of some versioning issues, I had to run 'aclocal' prior to
+running the kconfig-frontends configure script.  See "Configuring NuttX"
+below for further information.
+
+Unlike Cygwin, MSYS does not support symbolic links.  The 'ln -s' command
+will, in fact, copy a directory!  This means that you Make.defs file will
+have to include definitions like:
+
+    ifeq ($(CONFIG_WINDOWS_MSYS),y)
+      DIRLINK = $(TOPDIR)/tools/copydir.sh
+      DIRUNLINK = $(TOPDIR)/tools/unlink.sh
+    endif
+
+This will force the directory copies to work in a way that can be handled
+by the NuttX build system.  NOTE:  The default link.sh script has been
+updated so that is should now be MSYS2 compatible.  The above is preferred
+but no longer necessary in the Make.defs file.
+
+To build the simulator under MSYS, you also need:
+
+    pacman -S zlib-devel
+
+It appears that you cannot use directory names with spaces in them like
+"/c/Program\ Files \(86\)" in the MSYS path variable.  I worked around this
+by create Windows junctions like this:
+
+  1. Open the a windows command terminal,
+  
+  2. CD to `c:\msys64`, then
+  
+  3. `mklink /j programfiles "C:/Program\ Files"` and
+  
+  4. `mklink /j programfiles86 "C:/Program\ Files\ \(x86\)"`
+     
+     They then show up as `/programfiles` and `/programfiles86` with the MSYS2
+     sandbox.  Those paths can then be used with the PATH variable.  I had
+     to do something similar for the path to the GNU Tools "ARM Embedded
+     Toolchain" which also has spaces in the path name.
+
+## Ubuntu Bash under Windows 10
+
+A better version of a command-line only Ubuntu under Windows 10 (beta)
+has recently been made available from Microsoft.
+
+### Installation
+
+Installation instructions abound on the Internet complete with screen
+shots.  I will attempt to duplicate those instructions in full here.
+Here are the simplified installation steps:
+
+  - Open *Settings*.
+  
+  - Click on *Update & security*.
+  
+  - Click on *For Developers*.
+  
+  - Under *Use developer features*, select the *Developer mode* option to
+    setup the environment to install Bash.
+  
+  - A message box should pop up.  Click *Yes* to turn on developer mode.
+  
+  - After the necessary components install, you'll need to restart your
+    computer.
+    
+    Once your computer reboots:
+  
+  - Open *Control Panel*.
+  
+  - Click on *Programs*.
+  
+  - Click on *Turn Windows features on or off*.
+  
+  - A list of features will pop up, check the *Windows Subsystem for Linux
+    (beta)* option.
+  
+  - Click *OK*.
+  
+  - Once the components installed on your computer, click the *Restart
+    now* button to complete the task.
+    
+    After your computer restarts, you will notice that Bash will not appear in
+    the *Recently added* list of apps, this is because Bash isn't actually
+    installed yet. Now that you have setup the necessary components, use the
+    following steps to complete the installation of Bash:
+  
+  - Open *Start*, do a search for `bash.exe`, and press *Enter*.
+  
+  - On the command prompt, type `y` and press Enter to download and install
+    Bash from the Windows Store.  This will take awhile.
+  
+  - Then you'll need to create a default UNIX user account. This account
+    doesn't have to be the same as your Windows account. Enter the
+    username in the required field and press Enter (you can't use the
+    username `admin`).
+  
+  - Close the `bash.exe` command prompt.
+  
+  Now that you completed the installation and setup, you can open the Bash
+  tool from the Start menu like you would with any other app.
+
+### Accessing Windows Files from Ubuntu
+
+File systems will be mounted under `/mnt` so for example `C:\Program Files`
+appears at `/mnt/c/Program Files`.  This is as opposed to Cygwin where
+the same directory would appear at `/cygdrive/c/Program Files`.
+
+With these differences (perhaps a few other Windows quirks) the Ubuntu
+install works just like Ubuntu running natively on your PC.
+
+A good tip for file sharing is to use symbolic links within your Ubuntu
+home directory.  For example, suppose you have your `projects` directory
+at `C:\Documents\projects`.  Then you can set up a link to the `projects/`
+directory in your Ubuntu directory like:
+
+    ln -s /mnt/c/Documents/projects projects
+
+### Accessing Ubuntu Files From Windows
+
+In Ubuntu Userspace for Windows, the Ubuntu file system root directory is
+at:
+
+    %localappdata%\lxss\rootfs
+
+Or
+
+    C:\Users\Username\AppData\Local\lxss\rootfs
+
+However, I am unable to see my files under the rootfs\home directory.
+After some looking around, I find the home directory
+`%localappdata%\lxss\home`.
+
+With that trick access to the `/home` directory, you should actually be
+able to use Windows tools outside of the Ubuntu sandbox with versions of
+NuttX built within the sandbox using that path.
+
+### Executing Windows Tools from Ubuntu
+
+You can also execute Windows tools from within the Ubuntu sandbox:
+
+    /mnt/c/Program\ Files\ \(x86\)/Microchip/xc32/v1.43/bin/xc32-gcc.exe --version
+    Unable to translate current working directory. Using C:\WINDOWS\System32
+    xc32-gcc.exe (Microchip Technology) 4.8.3 MPLAB XC32 Compiler v1.43 Build date: Mar  1 2017
+    ...
+
+The error message indicates that there are more issues:  You cannot mix
+Windows tools that use Windows style paths in an environment that uses
+POSIX paths.  I think you would have to use Linux tools only from within
+the Ubuntu sandbox.
+
+### Install Ubuntu Software
+
+Use `sudo apt-get install <package name>`.  As examples, this is how
+you would get GIT:
+
+    sudo apt-get install git
+
+This will get you a compiler for your host PC:
+
+    sudo apt-get install gcc
+
+This will get you an ARM compiler for your target:
+
+    sudo apt-get install gcc-arm-none-eabi
+
+**NOTE**: That is just an example.  I am not sure if apt-get will give you a
+current or usable compiler.  You should carefully select your toolchain
+for the needs of your project.
+
+You will also need to get the kconfig-frontends configuration as
+described below under *NuttX Configuration Tool*.  In order to build the
+kconfig-frontends configuration tool you will also need: `make`, `gperf`,
+`flex`, `bison`, and `libncurses-dev`.
+
+That is enough to do a basic NuttX build.
+
+### Integrating with Windows Tools
+
+If you want to integrate with Windows native tools, then you would need
+deal with the same kind of craziness as with integrating Cygwin with
+native toolchains, see the section *Cygwin Build Problems* below.
+
+However, there is currently no build support for using Windows native
+tools with Ubuntu under Windows.  This tool combination is made to work
+with Cygwin through the use of the `cygpath -w` tool that converts paths
+from say `/cydrive/c/Program Files` to `C:\Program Files`.  There is,
+however, no corresponding tool to convert `/mnt/c/Program Files` in the
+Ubuntu environment.
+
+### Graphics Support
+
+The Ubuntu version support by Microsoft is a command-line only version.
+There is no support for Linux graphics utilities.
+
+This limitation is not a limitation of Ubuntu, however, only in what
+Microsoft is willing to support.  If you install a X-Server, then you
+can also use basic graphics utilities.  See for example:
+
+  <http://www.howtogeek.com/261575/how-to-run-graphical-linux-desktop-applications-from-windows-10s-bash-shell/>
+
+Many Linux graphics programs would, however, also require a graphics
+framework like GTK or Qt.  So this might be a trip down the rabbit hole.
+
+### Using macOS
+
+You need to install at least the following tools specific to macOS.
+
+  * flock (used by APPDIR build logic)
+    
+A macOS port is available at: <https://github.com/discoteq/flock>
+  
+    brew tap discoteq/discoteq
+    brew install flock
+  
+  If you want to build the sim:
+
+  * Xcode (the native compiler and the rest of the toolchain)
+
+  * ELF toolchain (if you want to build modules for CONFIG_LIBC_MODLIB)
+
+    brew install x86_64-elf-gc
+
+# INSTALLATION
+
+There are two ways to get NuttX:  You may download released, stable
+tarballs from either the project website.  Or you may get NuttX by
+cloning the GIT repositories.  Let's consider the released tarballs
+first:
+
+## Download and Unpack
+
+Download and unpack the NuttX tarball.  If you are reading this, then
+you have probably already done that.  After unpacking, you will end
+up with a directory called nuttx-version (where version is the NuttX
+version number). You might want to rename that directory nuttx to
+match the various instructions in the documentation and some scripts
+in the source tree.
+
+  * Download location:
+  
+    <https://nuttx.apache.org/download/>
+  
+  * Legacy download locations:
+
+    <https://bitbucket.org/nuttx/nuttx/downloads>  
+    <https://sourceforge.net/projects/nuttx/files/nuttx/>
+
+## Semi-Optional apps/ Package
+
+All NuttX libraries and example code used to be in included within
+the NuttX source tree.  As of NuttX-6.0, this application code was
+moved into a separate tarball, the apps tarball.  If you are just
+beginning with NuttX, then you will want to download the versioned
+apps tarball along with the NuttX tarball.  If you already have your
+own product application directory, then you may not need the apps
+tarball.
+
+It is called "Semi-optional" because if you don't have some `apps/`
+directory, NuttX will *fail* to build! You do not necessarily need
+to use the NuttX apps tarball but may, instead, provide your own
+custom application directory.  Such a custom directory would need
+to include a valid Makefile to support the build and a valid Kconfig
+file to support the configuration.  More about these files later.
+
+Download then unpack the apps tarball in the same directory where you
+unpacked the NuttX tarball.  After you unpack the apps tarball, you
+will have a new directory called apps-version (where the version
+should exactly match the version of the NuttX tarball).  Again, you
+might want to rename the directory to simply apps/ to match what
+you read in the documentation
+
+After unpacking (and renaming) the apps tarball, you will have two
+directories side by side like this:
+
+             |
+        +----+----+
+        |         |
+      nuttx/     apps/
+
+This is important because the NuttX build will expect to find the
+apps directory in that (default) location.  That default location
+can be changed by modifying your NuttX configuration file, but that
+is another story.
+
+## Installation Directories with Spaces in the Path
+
+The nuttx build directory should reside in a path that contains no
+spaces in any higher level directory name.  For example, under
+Cygwin, your home directory might be formed from your first and last
+names like: `/home/First Last`. That will cause strange errors when
+the make system tries to build.
+
+[Actually, that problem is probably not too difficult to fix.  Some
+ Makefiles probably just need some paths within double quotes]
+
+I work around spaces in the home directory name, by creating a
+new directory that does not contain any spaces, such as `/home/nuttx`.
+Then I install NuttX in `/home/nuttx` and always build from
+`/home/nuttx/nuttx-code`.
+
+## Downloading from Repositories
+
+### Cloning the Repository
+
+**BEFORE** cloning repositories on any Windows platform do the following GIT
+command:
+
+    git config --global core.autocrlf false
+
+That will avoid conversions of linefeeds (newlines, \n) to carriage
+return plus linefeed sequences (\r\n)
+
+The current NuttX du jour is available in from a GIT repository.  Here are
+instructions for cloning the core NuttX RTOS (corresponding to the nuttx
+tarball discussed above):
+
+    git clone https://gitbox.apache.org/repos/asf/incubator-nuttx.git nuttx
+
+-or-
+
+    git clone https://github.com/apache/incubator-nuttx.git nuttx
+
+And the semi-optional apps/ application directory and be cloned like:
+
+    git clone https://gitbox.apache.org/repos/asf/incubator-nuttx-apps.git apps
+  
+-or-
+  
+    git clone https://github.com/apache/incubator-nuttx-apps.git apps
+
+That will give you the same directory structure like this:
+    
+             |
+        +----+----+
+        |         |
+      nuttx/     apps/
+
+### Configuring the Clones
+
+The following steps need to be performed for each of the repositories.
+After changing to the clone directory:
+
+Set your identity:
+
+    git config --global user.name "My Name"
+    git config --global user.email my.name@example.com
+  
+Colorized diffs are much easier to read:
+
+    git config --global color.branch auto
+    git config --global color.diff auto
+    git config --global color.interactive auto
+    git config --global color.status auto
+
+Checkout other settings
+
+    git config --list
+
+### Cloning NuttX Inside Cygwin
+
+If you are cloning the NuttX repository, it is recommended to avoid
+automatic end of lines conversions by git. These conversions may break
+some scripts like configure.sh. Before cloning, do the following:
+
+    git config --global core.autocrlf false
+
+## Related Repositories
+
+These are standalone repositories:
+
+  * <https://gitbox.apache.org/repos/asf/incubator-nuttx-apps>  
+    or  
+    <https://github.com/apache/incubator-nuttx-apps.git>
+    
+    This directory holds an optional package of applications and libraries
+    can be used with the NuttX RTOS.  There is a README.txt file there that
+    will provide more information about that package.
+
+  * <https://bitbucket.org/nuttx/nxwidgets>
+  
+    This is the NuttX C++ graphics support.  This includes NxWM, the tiny
+    NuttX Window Manager.
+
+  * <https://bitbucket.org/nuttx/uclibc>
+  
+    This repository contains a version of the uClibc++ C++ library.  This code
+    originates from <http://cxx.uclibc.org/> and has been adapted for NuttX by the
+    RGMP team (<http://rgmp.sourceforge.net/wiki/index.php/Main_Page>).
+
+  * <https://bitbucket.org/nuttx/buildroot>
+  
+    A environment that you can to use to build a custom, NuttX GNU toolchain.
+
+  * <https://bitbucket.org/nuttx/tools>
+  
+    There are snapshots of some tools here that you will need to work with
+    NuttX:  kconfig-frontends, genromfs, and others.
+
+## Notes about Header Files
+
+### Other C-Library Header Files
+
+When a GCC toolchain is built, it must be built against a C library.
+The compiler together with the contents of the C library completes the
+C language definition and provides the complete C development
+environment.  NuttX provides its own, built-in C library.  So the
+complete, consistent C language definition for use with NuttX comes from
+the combination of the compiler and the header files provided by the
+NuttX C library.
+
+When a GCC toolchain is built, it incorporates the C library header
+files into the compiler internal directories and, in this way, the C
+library really becomes a part of the toolchain.  If you use the NuttX
+buildroot toolchain as described below under "NuttX Buildroot
+Toolchain", your GCC toolchain will build against the NuttX C library
+and will incorporate the NuttX C library header files as part of the
+toolchain.
+
+If you use some other, third-party tool chain, this will not be the
+case, however.  Those toolchains were probably built against some
+other, incompatible C library distribution (such as newlib).  Those
+tools will have incorporated the incompatible C library header files
+as part of the toolchain.  These incompatible header files must *not*
+be used with NuttX because they will conflict with definitions in the
+NuttX built-in C-Library.  For such toolchains that include header
+files from a foreign C-Library, NuttX must be compiled without using
+the standard header files that are distributed with your toolchain.
+This prevents including conflicting, incompatible header files such
+as stdio.h.
+
+The math.h and stdarg.h are probably the two most trouble some header
+files to deal with.  These troublesome header files are discussed in
+more detail below.
+
+### Header Files Provided by Your Toolchain
+
+Certain header files, such as `setjmp.h`, `stdarg.h`, and `math.h`, may still
+be needed from your toolchain and your compiler may not, however, be able
+to find these if you compile NuttX without using standard header files
+(i.e., with `-nostdinc`).  If that is the case, one solution is to copy
+those header file from your toolchain into the NuttX include directory.
+
+### Duplicated Header Files
+
+There are also a few header files that can be found in the `nuttx/include`
+directory which are duplicated by the header files from your toolchain.
+stdint.h and stdbool.h are examples.  If you prefer to use the `stdint.h`
+and `stdbool.h` header files from your toolchain, those could be copied
+into the `nuttx/include/` directory. Using most other header files from
+your toolchain would probably cause errors.
+
+### math.h
+
+Even though you should not use a foreign C-Library, you may still need
+to use other, external libraries with NuttX.  In particular, you may
+need to use the math library, libm.a.  NuttX supports a generic, built-in
+math library that can be enabled using `CONFIG_LIBM=y`.  However, you may
+still want to use a higher performance external math library that has
+been tuned for your CPU.  Sometimes such tuned math libraries are
+bundled with your toolchain.
+
+The math library header file, `math.h`, is a then special case.  If you do
+nothing, the standard math.h header file that is provided with your
+toolchain will be used.
+
+If you have a custom, architecture specific math.h header file, then
+that header file should be placed at `arch/<cpu>/include/math.h`.  There
+is a stub `math.h` header file located at `include/nuttx/lib/math.h`.  This stub
+header file can be used to "redirect" the inclusion to an architecture-
+specific math.h header file.  If you add an architecture specific math.h
+header file then you should also define `CONFIG_ARCH_MATH_H=y` in your
+NuttX Configuration file.  If `CONFIG_ARCH_MATH_H` is selected, then the
+top-level Makefile will copy the stub math.h header file from
+`include/nuttx/lib/math.h` to `include/math.h` where it will become the system
+`math.h` header file.  The stub `math.h` header file does nothing other
+than to include that architecture-specific `math.h` header file as the
+system `math.h` header file.
+
+### float.h
+
+If you enable the generic, built-in math library, then that math library
+will expect your toolchain to provide the standard `float.h` header file.
+The float.h header file defines the properties of your floating point
+implementation.  It would always be best to use your toolchain's `float.h`
+header file but if none is available, a default `float.h` header file will
+be provided if this option is selected.  However, there is no assurance
+that the settings in this `float.h` are actually correct for your platform!
+
+### stdarg.h
+
+In most cases, the correct version of stdarg.h is the version provided
+with your toolchain.  However, sometimes there are issues with
+using your toolchains `stdarg.h`.  For example, it may attempt to draw in
+header files that do not exist in NuttX or perhaps the header files that
+it uses are not compatible with the NuttX header files.  In those cases,
+you can use an architecture-specific `stdarg.h` header file by defining
+`CONFIG_ARCH_STDARG_H=y`.
+
+See the discussion above for the `math.h` header.  This setting works
+exactly the same for the `stdarg.h` header file.
+
+# CONFIGURING NUTTX
+
+## Instantiating "Canned" Configurations
+
+### `configure.sh` and `configure.bat`
+
+"Canned" NuttX configuration files are retained in:
+
+    boards/<arch-name>/<chip-name>/<board-name>/configs/<config-dir>
+
+Where `<board-name>` is the name of your development board and `<config-dir>`
+is the name of the sub-directory containing a specific configuration for
+that board. `<arch-name>` and `<chip-name>` refer to characteristics of the
+MCU used on the board: `<arch-name>` is the CPU architecture implemented
+by the MCU; `<chip-name>` identifies the MCU chip family.  Only a few
+steps are required to instantiate a NuttX configuration, but to make the
+configuration even easier there are scripts available in the tools/
+sub-directory combines those simple steps into one command.
+
+There is one tool for use with any Bash-like shell that does configuration
+steps.  It is used as follows:
+
+    tools/configure.sh <board-name>:<config-dir>
+
+There is an alternative Windows batch file that can be used in the windows
+native environment like:
+
+    tools\configure.bat <board-name>:<config-dir>
+
+And, to make sure that other platforms are supported, there is also a
+C program at tools/configure.c that can be compiled to establish the
+board configuration.
+
+See `tools/README.txt` for more information about these scripts.
+
+General information about configuring NuttX can be found in:
+
+    {TOPDIR}/boards/README.txt
+    {TOPDIR}/boards/<arch-name>/<chip-name>/<board-name>/README.txt
+
+### The Hidden Configuration Scripts:
+
+As mentioned above, there are only a few simple steps to instantiating a
+NuttX configuration.  Those steps are hidden by the configuration scripts
+but are summarized below:
+  
+  1. Copy Files
+  
+     Configuring NuttX requires only copying two files from the
+     `<config-dir>` to the directory where you installed NuttX (TOPDIR):
+  
+       * Copy `boards/<arch-name>/<chip-name>/<board-name>/configs/<config-dir>/Make.def` to `{TOPDIR}/Make.defs`
+    
+         OR
+    
+       * Copy `boards/<arch-name>/<chip-name>/<board-name>/scripts/Make.def`
+         to `{TOPDIR}/Make.defs`
+    
+         Make.defs describes the rules needed by your tool chain to compile
+         and link code.  You may need to modify this file to match the
+         specific needs of your toolchain.  NOTE that a configuration may
+         have its own unique Make.defs file in its configuration directory or
+         it may use a common Make.defs file for the board in the scripts/
+         directory.  The first takes precedence.
+    
+       * Copy `boards/<arch-name>/<chip-name>/<board-name>/configs/<config-dir>/defconfig` to `{TOPDIR}/.config`
+    
+         The defconfig file holds the actual build configuration.  This
+         file is included by all other make files to determine what is
+         included in the build and what is not.  This file is also used
+         to generate a C configuration header at `include/nuttx/config.h`.
+    
+       * Copy other, environment-specific files to `{TOPDIR}`
+    
+         This might include files like .gdbinit or IDE configuration files
+         like .project or .cproject.
+  
+  2. Refresh the Configuration
+  
+     New configuration setting may be added or removed.  Existing settings
+     may also change there values or options.  This must be handled by
+     refreshing the configuration as described below.
+    
+     NOTE:  NuttX uses only compressed defconfig files.  For the NuttX
+     defconfig files, this refreshing step is *NOT* optional; it is also
+     necessary to uncompress and regenerate the full making file.  This is
+     discussed further below.
+
+## Refreshing Configurations
+
+Configurations can get out of date.  As new configuration settings are
+added or removed or as dependencies between configuration settings
+change, the contents of a default configuration can become out of synch
+with the build systems.  Hence, it is a good practice to "refresh" each
+configuration after configuring and before making.  To refresh the
+configuration, use the NuttX Configuration Tool like this:
+
+    make oldconfig
+
+AFTER you have instantiated the NuttX configuration as described above.
+The configuration step copied the .config file into place in the top-level
+NuttX directory; 'make oldconfig' step will then operate on that .config
+file to bring it up-to-date.
+
+If your configuration is out of date, you will be prompted by 'make oldconfig'
+to resolve the issues detected by the configuration tool, that is, to
+provide values for the new configuration options in the build system.  Doing
+this can save you a lot of problems down the road due to obsolete settings in
+the default board configuration file.  The NuttX configuration tool is
+discussed in more detail in the following paragraph.
+
+Confused about what the correct value for a new configuration item should
+be?  Enter ? in response to the 'make oldconfig' prompt and it will show
+you the help text that goes with the option.
+
+If you don't want to make any decisions are willing to just accept the
+recommended default value for each new configuration item, an even easier
+way is:
+
+    make olddefconfig
+
+The olddefconfig target will simply bring your configuration up to date with
+the current Kconfig files, setting any new options to the default value.
+No questions asked.
+
+## NuttX Configuration Tool
+
+An automated tool has been incorporated to support re-configuration
+of NuttX.  This tool is based on the kconfig-frontends application available
+at <https://bitbucket.org/nuttx/tools/src/master/kconfig-frontends/>.  (This
+is a snapshot of the old <http://ymorin.is-a-geek.org/projects/kconfig-frontends>
+which is no longer available.)  This application provides a tool called
+`kconfig-mconf` that is used by the NuttX top-level Makefile. The following
+make target is provided:
+
+    make menuconfig
+
+This make target will bring up NuttX configuration menus.
+
+**WARNING**:  Never do `make menuconfig` on a configuration that has
+not been converted to use the kconfig-frontends tools!  This will
+damage your configuration (see
+<http://www.nuttx.org/doku.php?id=wiki:howtos:convertconfig>).
+
+How do we tell a new configuration from an old one? See "Incompatibilities
+with Older Configurations" below.
+
+The `menuconfig` make target depends on two things:
+
+  1. The Kconfig configuration data files that appear in almost all
+     NuttX directories.  These data files are the part that is still
+     under development (patches are welcome!).  The Kconfig files
+     contain configuration information for the configuration settings
+     relevant to the directory in which the Kconfig file resides.
+     
+     NOTE: For a description of the syntax of this configuration file,
+     see kconfig-language.txt in the tools repository at
+     <https://bitbucket.org/nuttx/tools>
+  
+  2. The `kconfig-mconf` tool. `kconfig-mconf` is part of the
+     kconfig-frontends package.  You can download that package from the
+     snapshot in the tools repository at <https://bitbucket.org/nuttx/tools>.
+  
+     Building kconfig-frontends under Linux may be as simple as
+     `configure; make; make install` but there may be some build
+     complexities, especially if you are building under Cygwin.  See
+     the more detailed build instructions in the top-level README.txt
+     file of the tools repository at <https://bitbucket.org/nuttx/tools>.
+  
+  
+     The `make install` step will, by default, install the `kconfig-mconf`
+     tool at `/usr/local/bin/mconf`.  Where ever you choose to
+     install `kconfig-mconf`, make certain that your PATH variable includes
+     a path to that installation directory.
+  
+     The kconfig-frontends tools will not build in a native Windows
+     environment directly "out-of-the-box".  For the Windows native
+     case, you can use the modified version of kconfig-frontends
+     that can be found at
+
+     <http://uvc.de/posts/linux-kernel-configuration-tool-kconfig-under-windows.html>  
+
+     or a more recent port that can be found at  
+
+     <http://reclonelabs.com/more-kconfig-awesomeness-for-windows/>.
+   
+The basic configuration order is "bottom-up":
+   
+   - Select the build environment,
+   - Select the processor,
+   - Select the board,
+   - Select the supported peripherals
+   - Configure the device drivers,
+   - Configure the application options on top of this.
+   
+This is pretty straight forward for creating new configurations
+but may be less intuitive for modifying existing configurations.
+
+Another ncurses-based tool that is an option to kconfig-mconf is
+kconfig-nconf.  The differences are primary in in the aesthetics of the
+UI.  If you have kconfig-nconf built, then you can invoke that front end
+with:
+   
+     make nconfig
+   
+If you have an environment that supports the Qt or GTK graphical systems
+(probably KDE or gnome, respectively, or Cygwin under Windows with Qt or
+GTK installed), then you can also build the graphical kconfig-frontends,
+kconfig-qconf and kconfig-gconf.  In these case, you can start the
+graphical configurator with either:
+   
+     make qconfig
+   
+ or
+   
+     make gconfig
+   
+Some keyboard shortcuts supported by kconfig-mconf, the tool that runs
+when you do 'make menuconfig':
+
+   - `?` will bring up the mconfig help display.
+   
+   - `/` can be used find configuration selections.
+   
+   - `Z` can be used to reveal hidden configuration options
+   
+These last two shortcuts are described further in the following
+paragraphs.
+
+## Finding Selections in the Configuration Menus
+
+The NuttX configuration options have gotten complex and it can be very
+difficult to find options in the menu trees if you are not sure where
+to look.  The "basic configuration order" describe above can help to
+narrow things down.
+
+But if you know exactly what configuration setting you want to select,
+say CONFIG_XYZ, but not where to find it, then the 'make menuconfig'
+version of the tool offers some help:  By pressing the '/' key, the
+tool will bring up a menu that will allow you to search for a
+configuration item.  Just enter the string CONFIG_XYZ and press 'ENTER'.
+It will show you not only where to find the configuration item, but
+also all of the dependencies related to the configuration item.
+
+## Reveal Hidden Configuration Options
+
+If you type `Z`, then kconfig-mconf will change what is displayed.
+Normally, only enabled features that have all of their dependencies met
+are displayed.  That is, of course, not very useful if you would like to
+discover new options or if you are looking for an option and do not
+realize that the dependencies have not yet been selected and, hence, it
+is not displayed.
+
+But if you enter `Z`, then every option will be shown, whether or not its
+dependencies have been met.  You can then see everything that could be
+selected with the right dependency selections.  These additional options
+will be shown the `-` for the selection and for the value (since it
+cannot be selected and has no value).  About all you do is to select
+the `<Help>` option to see what the dependencies are.
+
+## Make Sure that You are on the Right Platform
+
+Saved configurations may run on Linux, Cygwin (32- or 64-bit), or other
+platforms.  The platform characteristics can be changed use `make
+menuconfig`.  Sometimes this can be confusing due to the differences
+between the platforms.  Enter sethost.sh
+
+sethost.sh is a simple script that changes a configuration to your
+host platform.  This can greatly simplify life if you use many different
+configurations.  For example, if you are running on Linux and you
+configure like this:
+
+    tools/configure.sh board:configuration
+
+The you can use the following command to both (1) make sure that the
+configuration is up to date, AND (2) the configuration is set up
+correctly for Linux:
+
+    tools/sethost.sh -l
+
+Or, if you are on a Windows/Cygwin 64-bit platform:
+
+    tools/sethost.sh -c
+
+Or, for MSYS/MSYS2:
+
+    tools/sethost.sh -g
+
+Other options are available from the help option built into the
+script.  You can see all options with:
+
+    tools/sethost.sh -h
+
+Recently, the options to the configure.sh (and configure.bat) scripts have
+been extended so that you both setup the configuration, select for the host
+platform that you use, and uncompress and refresh the defconfig file all in
+one command like:
+
+    tools/configure.sh -l board:configuration
+
+For a Linux host or for a Windows/Cygwin host:
+
+    tools/configure.sh -c board:configuration
+
+Other options are available from the help option built into the
+script.  You can see all options with:
+
+    tools/configure.sh -h
+
+## Comparing Two Configurations
+
+If you try to compare two configurations using 'diff', you will probably
+not be happy with the result.  There are superfluous things added to
+the configuration files that make comparisons with the human eye
+difficult.
+
+There is a tool at nuttx/tools/cmpconfig.c that can be built to simplify
+these comparisons.  The output from this difference tool will show only
+the meaningful differences between two configuration files.  This tool is
+built as follows:
+
+    cd nuttx/tools
+    make -f Makefile.host
+
+This will create a program called 'cmpconfig' or 'comconfig.exe' on Windows.
+
+Why would you want to compare two configuration files?  Here are a few
+of the reasons why I do this
+
+  1. When I create a new configuration I usually base it on an older
+     configuration and I want to know, "What are the options that I need to
+     change to add the new feature to the older configurations?"  For example,
+     suppose that I have a boardA/nsh configuration and I want to create a
+     boardA/nxwm configuration.  Suppose I already have boardB/nsh and
+     boardB/nxwm configurations.  Then by comparing the boardB/nsh with the
+     boardB/nxwm I can see the modifications that I would need to make to my
+     boardA/nsh to create a new  boardA/nxwm.
+  
+  2. But the most common reason that I use the 'cmpconfig' program is to
+     check the results of "refreshing" a configuration with 'make oldconfig'
+     (see the paragraph "Refreshing Configurations" above).  The 'make
+     oldconfig' command will make changes to my configuration and using
+     'cmpconfig', I can see precisely what those changes were and if any
+     should be of concern to me.
+  
+  3. The 'cmpconfig' tool can also be useful when converting older, legacy
+     manual configurations to the current configurations based on the
+     kconfig-frontends tools.  See the following paragraph.
+
+## Making defconfig Files
+
+### .config Files as defconfig Files:
+
+The minimum defconfig file is simply the generated .config file with
+CONFIG_APPS_DIR setting removed or commented out.  That setting provides
+the name and location of the apps/ directory relative to the nuttx build
+directory.  The default is ../apps/, however, the apps directory may be
+any other location and may have a different name.  For example, the name
+of versioned NuttX releases are always in the form apps-xx.yy where xx.yy
+is the version number.
+
+### Finding the apps/ Directory Path:
+
+When the default configuration is installed using one of the scripts or
+programs in the NuttX tools directory, there will be an option to provide
+the path to the apps/ directory.  If not provided, then the configure tool
+will look around and try to make a reasonable decision about where the
+apps/ directory is located.
+
+### Compressed defconfig Files:
+
+The Makefile also supports an option to generate very small defconfig
+files.  The .config files are quite large and complex.  But most of the
+settings in the .config file simply have the default settings from the
+Kconfig files.  These .config files can be converted into small defconfig
+file:
+    
+    make savedefconfig
+    
+That make target will generate a defconfig file in the top-level
+directory.  The size reduction is really quite remarkable:
+    
+    wc -l .config defconfig
+     1085 .config
+       82 defconfig
+     1167 total
+    
+In order to be usable, the .config file installed from the compressed
+defconfig file must be reconstituted using:
+    
+    make olddefconfig
+    
+  > **NOTE 1**:  Only compressed defconfig files are retained in the NuttX repository.
+  > All patches and PRs that attempt to add or modify a defconfig file MUST
+  > use the compressed defconfig format as created by 'make savdefconfig.'
+    
+  > **NOTE 2**:  When 'make savedefconfig' runs it will try several things some of
+  > which are expected to fail.  In these cases you will see an error message
+  > from make followed by "(ignored)."  You should also ignore these messages
+    
+**CAUTION**:  This size reduction was accomplished by removing all setting
+from the .config file that were at the default value.  'make olddefconfig'
+can regenerate the original .config file by simply restoring those default
+settings.  The underlying assumption here is, of course, that the default
+settings do not change.  If the default settings change, and they often
+do, then the original .config may not be reproducible.
+
+So if your project requires 100% reproducibility over a long period of
+time, you make want to save the complete .config files vs. the standard,
+compressed defconfig file.
+
+### Configuring with "Compressed" defconfig Files:
+
+As described above defconfig, all NuttX defconfig files are compressed
+using 'make savedeconfig'.  These compressed defconfig files are
+generally not fully usable as they are and may not build the target
+binaries that you want because the compression process removed all of
+the default settings from the defconfig file.  To restore the default
+settings, you should run the following after configuring:
+
+    make olddefconfig
+
+That will restore the the missing defaulted values.
+
+Using this command after configuring is generally a good practice anyway:
+Even if the defconfig files are not "compressed" in this fashion, the
+defconfig file may be old and the only way to assure that the installed
+.config is is up to date is via 'make oldconfig' or 'make olddefconfig'.
+See the paragraph above entitled ""Refreshing Configurations" for
+additional information.
+
+## Incompatibilities with Older Configurations
+
+**WARNING**
+
+The current NuttX build system supports *only* the new compressed,
+defconfig configuration files generated using the kconfig-frontends tools
+as described in the preceding section.  Support for the older, legacy,
+manual configurations was eliminated in NuttX 7.0; support for
+uncompressed .config-files-as-defconfig files was eliminated after
+NuttX-7.21.  All configurations must now be done using the
+kconfig-frontends tool.  The older manual configurations and the new
+kconfig-frontends configurations are not compatible.  Old legacy
+configurations can *not* be used with the kconfig-frontends tool and,
+hence, cannot be used with releases of NuttX 7.0 and beyond:
+
+If you run 'make menuconfig' with a legacy configuration the resulting
+configuration will probably not be functional.
+
+  > Q: How can I tell if a configuration is a new kconfig-frontends
+  >   configuration or an older, manual configuration?
+  >
+  > A: Only old, manual configurations will have an appconfig file
+  > 
+  > Q: How can I convert a older, manual configuration into a new,
+  >    kconfig-frontends toolchain.
+  >
+  > A: Refer to <http://www.nuttx.org/doku.php?id=wiki:howtos:convertconfig>
+  
+**WARNING**
+
+As described above, whenever you use a configuration, you really should
+always refresh the configuration with the following command *before* you
+make NuttX:
+
+    make oldconfig
+
+OR
+
+    make olddefconfig
+
+This will make sure that the configuration is up-to-date in the event that
+it has lapsed behind the current NuttX development (see the paragraph
+"Refreshing Configurations" above).  But this only works with *new*
+configuration files created with the kconfig-frontends tools.
+
+Further, this step is *NOT* optional with the new, compressed defconfig
+files.  It is a necessary step that will also uncompress the defconfig
+file, regenerating the .config and making it usable for NuttX builds.
+
+Never do `make oldconfig` (OR `make menuconfig`) on a  configuration that
+has not been converted to use the kconfig-frontends tools!  This will
+damage your configuration (see
+<http://www.nuttx.org/doku.php?id=wiki:howtos:convertconfig>).
+
+## NuttX Configuration Tool under DOS
+
+  Recent versions of NuttX support building NuttX from a native Windows
+  console window (see *Native Windows Build* below).  But kconfig-frontends
+  is a Linux tool.  At one time this was a problem for Windows users, but
+  now there are two specially modified versions of the kconfig-frontends
+  tools that can be used.  One can be found here:
+  <http://uvc.de/posts/linux-kernel-configuration-tool-kconfig-under-windows.html>
+
+  The configuration steps of the most recent versions of NuttX require the
+  kconfig-tweak tool that is not not available in the the above.  However,
+  there has been an update to this Kconfig Windows tools that does include
+  kconfig-tweak:  http://reclonelabs.com/more-kconfig-awesomeness-for-windows/
+
+  Source code is available here: <https://github.com/reclone/kconfig-frontends-win32>
+  and <https://github.com/reclone/kconfig-frontends-win32/releases>
+
+  It is also possible to use the version of kconfig-frontends built
+  under Cygwin outside of the Cygwin "sandbox" in a native Windows
+  environment:
+
+  1. You can run the configuration tool using Cygwin.  However, the
+     Cygwin Makefile.win will complain so to do this will, you have
+     to manually edit the .config file:
+     
+     a. Delete the line: CONFIG_WINDOWS_NATIVE=y
+     
+     b. Change the apps/ directory path, CONFIG_APPS_DIR to use Unix
+      
+        style delimiters.  For example, change "..\apps" to "../apps"
+     
+     And of course, after you use the configuration tool you need to
+     restore CONFIG_WINDOWS_NATIVE=y and the correct CONFIG_APPS_DIR.
+
+  2. You can, with some effort, run the Cygwin kconfig-mconf tool
+     directly in the Windows console window.  In this case, you do not
+     have to modify the .config file, but there are other complexities:
+     
+    a. You need to temporarily set the Cygwin directories in the PATH

Review comment:
       @v01d Indenting is wrong here... makes this all preformatted. I think the 'a.' needs to line up directly under the 'Y' in the '2. You...' above.

##########
File path: README.md
##########
@@ -0,0 +1,2513 @@
+# APACHE NUTTX (INCUBATING)
+
+* Introduction
+  - Incubation Status
+* Community
+  - Getting Help
+  - Mailing Lists
+  - Issue Tracker
+  - Source Code
+  - Website Source Code
+* Environments
+  - Installing Cygwin
+  - Ubuntu Bash under Windows 10
+  - Using macOS
+* Installation
+  - Download and Unpack
+  - Semi-Optional apps/ Package
+  - Installation Directories with Spaces in the Path
+  - Downloading from Repositories
+  - Related Repositories
+  - Notes about Header Files
+* Configuring NuttX
+  - Instantiating "Canned" Configurations
+  - Refreshing Configurations
+  - NuttX Configuration Tool
+  - Finding Selections in the Configuration Menus
+  - Reveal Hidden Configuration Options
+  - Make Sure that You are on the Right Platform
+  - Comparing Two Configurations
+  - Making defconfig Files
+  - Incompatibilities with Older Configurations
+  - NuttX Configuration Tool under DOS
+* Toolchains
+  - Cross-Development Toolchains
+  - NuttX Buildroot Toolchain
+* Shells
+* Building NuttX
+  - Building
+  - Re-building
+  - Build Targets and Options
+  - Native Windows Build
+  - Installing GNUWin32
+* Cygwin Build Problems
+  - Strange Path Problems
+  - Window Native Toolchain Issues
+* Documentation
+
+# INTRODUCTION
+
+Apache NuttX (Incubating) is a real-time operating system (RTOS) with an
+emphasis on standards compliance and small footprint.  Scalable from 8-bit
+to 32-bit microcontroller environments, the primary governing standards in
+NuttX are POSIX and ANSI standards. Additional standard APIs from Unix and
+other common RTOSs (such as VxWorks) are adopted for functionality not
+available under these standards, or for functionality that is not
+appropriate for deeply-embedded environments (such as fork()).
+
+Extensive documentation can be found on the project wiki:
+  <https://cwiki.apache.org/NUTTX/Nuttx>
+
+## Incubation Status
+
+Apache NuttX (Incubating) is an effort undergoing Incubation at The Apache
+Software Foundation (ASF), sponsored by the Incubator.  For more on our
+incubation effort, please see the file DISCLAIMER-WIP, in the same
+directory as this README.
+
+For brevity, the rest of this file will refer to it as Apache NuttX or
+simply NuttX.
+
+# COMMUNITY
+
+Every volunteer project obtains its strength from the people involved in
+it.  We invite you to participate as much or as little as you choose.
+
+We encourage you to:
+
+  - Use our project and provide feedback.
+  - Provide us with use-cases.
+  - Report bugs and submit patches.
+  - Contribute code or documentation.
+
+## Getting Help
+
+The best place to get help is the developer's mailing list.  Please see
+the following section:
+
+## Mailing Lists
+
+Get help using NuttX or contribute to the project on our mailing lists:
+
+  * <de...@nuttx.apache.org> is for people who want to contribute code to NuttX.
+    * To subscribe, send an email to <de...@nuttx.apache.org>.
+    * To unsubscribe, send an email to <de...@nuttx.apache.org>.
+    * View the archives at:
+      <https://www.mail-archive.com/dev@nuttx.apache.org/>
+
+  * <co...@nuttx.apache.org> is a read-only list that notifies subscribers
+  about commit messages and patches to NuttX.
+    * To subscribe, send an email to <co...@nuttx.apache.org>.
+    * To unsubscribe, send an email to <co...@nuttx.apache.org>.
+    * View the archives at:
+      <https://www.mail-archive.com/commits@nuttx.apache.org/>
+
+## Issue Tracker
+
+### Bug Reports:
+
+Found bug? Send an email to the dev list: <de...@nuttx.apache.org>
+
+Before submitting an issue, please:
+
+  - Verify that the bug does in fact exist. 
+  
+  - Search the mailing list archives to verify there is no existing issue
+    reporting the bug you've found.
+ 
+  - Consider tracking down the bug yourself in the NuttX source code and
+    submitting a patch along with your bug report.  This is a great time
+    saver for the NuttX developers and helps ensure the bug will be fixed
+    quickly.
+  
+### Feature Requests:
+  
+Enhancement requests for new features are also welcome. The more concrete
+and rational the request is, the greater the chance it will incorporated
+into future releases.
+
+## Source Code
+
+The project sources are in two Git repositories.  The core OS is in
+incubator-nuttx and the apps repository is in incubator-nuttx-apps.  These
+are housed in GitBox on ASF servers and also mirrored at GitHub.  These
+are kept in sync, so you can use whichever option you prefer.
+
+  - NuttX core OS repository:
+    
+    - Primary:
+      <https://gitbox.apache.org/repos/asf?p=incubator-nuttx.git>
+    
+    - GitHub Mirror:
+      <https://github.com/apache/incubator-nuttx>
+  
+  - Apps repository:
+    
+    - Primary:
+      <https://gitbox.apache.org/repos/asf?p=incubator-nuttx-apps.git>
+    
+    - GitHub Mirror:
+      <https://github.com/apache/incubator-nuttx-apps>
+
+## Website Source Code
+
+The project website sources are accessible via the website source code
+  repository which is also mirrored in GitHub:
+
+- Primary:
+  <https://gitbox.apache.org/repos/asf?p=incubator-nuttx-website.git>
+
+- GitHub Mirror:
+  <https://github.com/apache/incubator-nuttx-website>
+
+# ENVIRONMENTS
+
+  NuttX requires a POSIX development environment such as you would find under
+  Linux or macOS.  NuttX may also be installed and built on Windows system
+  if you also provide such a POSIX development environment.  Options for a
+  POSIX development environment under Windows include:
+
+  - An installation of Linux on a virtual machine (VM) in Windows.  I have
+    not been happy using a VM myself.  I have had stability problems with
+    open source VMs and commercial VMs cost more than I want to spend.
+    Sharing files with Linux running in a VM is awkward;  sharing devices
+    connected to the Windows box with Linux in a VM is, at the very least,
+    confusing;  Using Windows tools (such as Segger J-Link) with files
+    built under the Linux VM is not a possibility.
+
+  - The Cygwin environment.  Instructions for installation of Cygwin on a
+    Windows system are provided in the following paragraph, "Installing
+    Cygwin".  Cygwin is a mature, well-tested, and very convenient
+    environment.  It is especially convenient if you  need to
+    integrate with Windows tools and files.  Downsides are that the
+    installation time is very long and the compile times are slow.
+
+  - Ubuntu/Bash shell under Windows 10.  This is a new option under
+    Windows 10.  See the section "Ubuntu Bash under Windows 10" below.
+    This is an improvement over Cygwin if your concern is compile time;
+    its build performance is comparable to native Linux, certainly better
+    than the Cygwin build time.  It also installs in a tiny fraction of
+    the time as Cygwin, perhaps 20 minutes for the basic Ubuntu install
+    (vs. more than a day for the complete Cygwin install).
+  
+    There have been even more recent ports of Linux environment to
+    Windows.  I need to update this section to include some mention of
+    these alternatives.
+
+  - The MSYS environment.  MSYS derives from an older version of Cygwin
+    simplified and adapted to work more naturally in the Windows
+    environment.  See <http://www.mingw.org/wiki/MSYS> if you are
+    interested in using MSYS.  The advantages of the MSYS environment is
+    that it is better integrted with the native Windows environment and
+    lighter weight; it uses only a  minimal number of add-on POSIX-land
+    tools.
+  
+    The download link in that Wiki takes you to the SourceForge download
+    site.  The SourceForge MSYS project has been stagnant for some time.
+    The MSYS project has more recently moved to
+    <http://odsn.net/projects/sfnet_mingwbundle>.  Downloads of current .zip
+    files are available there but no instructions for the installation.
+
+  - MSYS2 appears to be a re-write of MSYS based on a newer version of
+    Cygwin.  Is it available at <https://www.msys2.org>.  A windows
+    installer is available at that site along with very good installation
+    instructions.  The download is relatively quick (at least compared to
+    Cygwin) and the 'pacman' package management tool supports supports
+    simple system updates.  For example, 'pacman -S git' will install the
+    GIT command line utilities.
+
+  - Other POSIX environments.  Check out:
+    
+    - UnxUtils: <https://sourceforge.net/projects/unxutils/>,
+      <https://en.wikipedia.org/wiki/UnxUtils>
+    - MobaXterm: <https://mobaxterm.mobatek.net/>
+    - Gow: <https://github.com/bmatzelle/gow/wiki>
+  
+    **Disclaimer**:  In principle, these should work.  However, I have never
+    used any of these environments and cannot guarantee that there is
+    not some less-than-obvious issues.
+  
+NuttX can also be installed and built on a native Windows system, but with
+some potential tool-related issues (see the discussion "Native Windows
+Build" under "Building NuttX" below).  GNUWin32 is used to provide
+compatible native windows tools.
+
+## Installing Cygwin
+
+Installing Cygwin on your Windows PC is simple, but time consuming.  See
+<http://www.cygwin.com/> for installation instructions. Basically you just
+need to download a tiny setup.exe program and it does the real, network
+installation for you.
+
+Some Cygwin installation tips:
+
+  1. Install at `C:\cygwin`
+  
+  2. Install **everything**:  "Only the minimal base packages from the
+     Cygwin distribution are installed by default. Clicking on categories
+     and packages in the setup.exe package installation screen will
+     provide you with the ability to control what is installed or updated.
+     Clicking on the "Default" field next to the "All" category will
+     provide you with the opportunity to install every Cygwin package.
+     Be advised that this will download and install hundreds of megabytes
+     to your computer."
+   
+If you use the "default" installation, you will be missing many
+of the Cygwin utilities that you will need to build NuttX.  The
+build will fail in numerous places because of missing packages.
+
+NOTE: The last time I installed **everything**, the download was
+about 5GiB.  The server I selected was also very slow so it took
+over a day to do the whole install!
+
+NOTE: You don't really have to install **everything** but I cannot
+answer the question "Then what should I install?"  I don't know
+the answer to that and so will continue to recommend installing
+**everything**.
+
+You should certainly be able to omit "Science", "Math", and
+"Publishing".  You can try omitting KDE, Gnome, GTK, and other
+graphics packages if you don't plan to use them.
+
+Perhaps a minimum set would be those packages listed below for the
+"Ubuntu Bash under Windows 10" installation?
+
+**UPDATE**:  Sergey Frolov had success with the following minimal
+Cygwin configuration:
+   
+   1. After starting the Cygwin installer, keep the recommended
+      packages that are pre-selected in the default configuration.
+   
+   2. Using the installation tools, add the following packages:
+      
+        make (GNU make)  bison        libgmp3-dev
+        gcc-core         byacc        libmpfr-dev
+        gcc-g++          gperf        libmpc-dev
+        flex             gdb          automake-1.15
+        libncurses-dev   libgmp-dev
+   
+After installing Cygwin, you will get lots of links for installed
+tools and shells.  I use the RXVT native shell.  It is fast and reliable
+and does not require you to run the Cygwin X server (which is neither
+fast nor reliable).  Unless otherwise noted, the rest of these
+instructions assume that you are at a bash command line prompt in
+either Linux or in Cygwin shell.
+
+## Using MSYS
+
+MSYS is an environment the derives from Cygwin.  Thus, most things said
+about Cygwin apply equally to MSYS.  This section will, then, focus on
+the differences when using MSYS, specifically MSYS2.
+
+Here is it assumed that you have already downloaded and installed MSYS2
+from https://www.msys2.org using the windows installer available at that
+location.  It is also assumed that you have brought in the necessary
+tools using the 'pacman' package management tool Tools needed including:
+
+  pacman -S git
+  pacman -S make
+  pacman -S gcc
+  pacman -S gdb
+
+And possibly others depending upon your usage.  Then you will need to
+build and install kconfig-frontends per the instructions of the top-level
+README.txt file in the tools repository.  This requires the following
+additional tools:
+
+    pacman -S bison
+    pacman -S gperf
+    pacman -S ncurses-devel
+    pacman -S automake-wrapper
+    pacman -S autoconf
+    pacman -S pkg-config
+
+Because of some versioning issues, I had to run 'aclocal' prior to
+running the kconfig-frontends configure script.  See "Configuring NuttX"
+below for further information.
+
+Unlike Cygwin, MSYS does not support symbolic links.  The 'ln -s' command
+will, in fact, copy a directory!  This means that you Make.defs file will
+have to include definitions like:
+
+    ifeq ($(CONFIG_WINDOWS_MSYS),y)
+      DIRLINK = $(TOPDIR)/tools/copydir.sh
+      DIRUNLINK = $(TOPDIR)/tools/unlink.sh
+    endif
+
+This will force the directory copies to work in a way that can be handled
+by the NuttX build system.  NOTE:  The default link.sh script has been
+updated so that is should now be MSYS2 compatible.  The above is preferred
+but no longer necessary in the Make.defs file.
+
+To build the simulator under MSYS, you also need:
+
+    pacman -S zlib-devel
+
+It appears that you cannot use directory names with spaces in them like
+"/c/Program\ Files \(86\)" in the MSYS path variable.  I worked around this
+by create Windows junctions like this:
+
+  1. Open the a windows command terminal,
+  
+  2. CD to `c:\msys64`, then
+  
+  3. `mklink /j programfiles "C:/Program\ Files"` and
+  
+  4. `mklink /j programfiles86 "C:/Program\ Files\ \(x86\)"`
+     
+     They then show up as `/programfiles` and `/programfiles86` with the MSYS2
+     sandbox.  Those paths can then be used with the PATH variable.  I had
+     to do something similar for the path to the GNU Tools "ARM Embedded
+     Toolchain" which also has spaces in the path name.
+
+## Ubuntu Bash under Windows 10
+
+A better version of a command-line only Ubuntu under Windows 10 (beta)
+has recently been made available from Microsoft.
+
+### Installation
+
+Installation instructions abound on the Internet complete with screen
+shots.  I will attempt to duplicate those instructions in full here.
+Here are the simplified installation steps:
+
+  - Open *Settings*.
+  
+  - Click on *Update & security*.
+  
+  - Click on *For Developers*.
+  
+  - Under *Use developer features*, select the *Developer mode* option to
+    setup the environment to install Bash.
+  
+  - A message box should pop up.  Click *Yes* to turn on developer mode.
+  
+  - After the necessary components install, you'll need to restart your
+    computer.
+    
+    Once your computer reboots:
+  
+  - Open *Control Panel*.
+  
+  - Click on *Programs*.
+  
+  - Click on *Turn Windows features on or off*.
+  
+  - A list of features will pop up, check the *Windows Subsystem for Linux
+    (beta)* option.
+  
+  - Click *OK*.
+  
+  - Once the components installed on your computer, click the *Restart
+    now* button to complete the task.
+    
+    After your computer restarts, you will notice that Bash will not appear in
+    the *Recently added* list of apps, this is because Bash isn't actually
+    installed yet. Now that you have setup the necessary components, use the
+    following steps to complete the installation of Bash:
+  
+  - Open *Start*, do a search for `bash.exe`, and press *Enter*.
+  
+  - On the command prompt, type `y` and press Enter to download and install
+    Bash from the Windows Store.  This will take awhile.
+  
+  - Then you'll need to create a default UNIX user account. This account
+    doesn't have to be the same as your Windows account. Enter the
+    username in the required field and press Enter (you can't use the
+    username `admin`).
+  
+  - Close the `bash.exe` command prompt.
+  
+  Now that you completed the installation and setup, you can open the Bash
+  tool from the Start menu like you would with any other app.
+
+### Accessing Windows Files from Ubuntu
+
+File systems will be mounted under `/mnt` so for example `C:\Program Files`
+appears at `/mnt/c/Program Files`.  This is as opposed to Cygwin where
+the same directory would appear at `/cygdrive/c/Program Files`.
+
+With these differences (perhaps a few other Windows quirks) the Ubuntu
+install works just like Ubuntu running natively on your PC.
+
+A good tip for file sharing is to use symbolic links within your Ubuntu
+home directory.  For example, suppose you have your `projects` directory
+at `C:\Documents\projects`.  Then you can set up a link to the `projects/`
+directory in your Ubuntu directory like:
+
+    ln -s /mnt/c/Documents/projects projects
+
+### Accessing Ubuntu Files From Windows
+
+In Ubuntu Userspace for Windows, the Ubuntu file system root directory is
+at:
+
+    %localappdata%\lxss\rootfs
+
+Or
+
+    C:\Users\Username\AppData\Local\lxss\rootfs
+
+However, I am unable to see my files under the rootfs\home directory.
+After some looking around, I find the home directory
+`%localappdata%\lxss\home`.
+
+With that trick access to the `/home` directory, you should actually be
+able to use Windows tools outside of the Ubuntu sandbox with versions of
+NuttX built within the sandbox using that path.
+
+### Executing Windows Tools from Ubuntu
+
+You can also execute Windows tools from within the Ubuntu sandbox:
+
+    /mnt/c/Program\ Files\ \(x86\)/Microchip/xc32/v1.43/bin/xc32-gcc.exe --version
+    Unable to translate current working directory. Using C:\WINDOWS\System32
+    xc32-gcc.exe (Microchip Technology) 4.8.3 MPLAB XC32 Compiler v1.43 Build date: Mar  1 2017
+    ...
+
+The error message indicates that there are more issues:  You cannot mix
+Windows tools that use Windows style paths in an environment that uses
+POSIX paths.  I think you would have to use Linux tools only from within
+the Ubuntu sandbox.
+
+### Install Ubuntu Software
+
+Use `sudo apt-get install <package name>`.  As examples, this is how
+you would get GIT:
+
+    sudo apt-get install git
+
+This will get you a compiler for your host PC:
+
+    sudo apt-get install gcc
+
+This will get you an ARM compiler for your target:
+
+    sudo apt-get install gcc-arm-none-eabi
+
+**NOTE**: That is just an example.  I am not sure if apt-get will give you a
+current or usable compiler.  You should carefully select your toolchain
+for the needs of your project.
+
+You will also need to get the kconfig-frontends configuration as
+described below under *NuttX Configuration Tool*.  In order to build the
+kconfig-frontends configuration tool you will also need: `make`, `gperf`,
+`flex`, `bison`, and `libncurses-dev`.
+
+That is enough to do a basic NuttX build.
+
+### Integrating with Windows Tools
+
+If you want to integrate with Windows native tools, then you would need
+deal with the same kind of craziness as with integrating Cygwin with
+native toolchains, see the section *Cygwin Build Problems* below.
+
+However, there is currently no build support for using Windows native
+tools with Ubuntu under Windows.  This tool combination is made to work
+with Cygwin through the use of the `cygpath -w` tool that converts paths
+from say `/cydrive/c/Program Files` to `C:\Program Files`.  There is,
+however, no corresponding tool to convert `/mnt/c/Program Files` in the
+Ubuntu environment.
+
+### Graphics Support
+
+The Ubuntu version support by Microsoft is a command-line only version.
+There is no support for Linux graphics utilities.
+
+This limitation is not a limitation of Ubuntu, however, only in what
+Microsoft is willing to support.  If you install a X-Server, then you
+can also use basic graphics utilities.  See for example:
+
+  <http://www.howtogeek.com/261575/how-to-run-graphical-linux-desktop-applications-from-windows-10s-bash-shell/>
+
+Many Linux graphics programs would, however, also require a graphics
+framework like GTK or Qt.  So this might be a trip down the rabbit hole.
+
+### Using macOS
+
+You need to install at least the following tools specific to macOS.
+
+  * flock (used by APPDIR build logic)
+    
+A macOS port is available at: <https://github.com/discoteq/flock>
+  
+    brew tap discoteq/discoteq
+    brew install flock
+  
+  If you want to build the sim:
+
+  * Xcode (the native compiler and the rest of the toolchain)
+
+  * ELF toolchain (if you want to build modules for CONFIG_LIBC_MODLIB)
+
+    brew install x86_64-elf-gc
+
+# INSTALLATION
+
+There are two ways to get NuttX:  You may download released, stable
+tarballs from either the project website.  Or you may get NuttX by
+cloning the GIT repositories.  Let's consider the released tarballs
+first:
+
+## Download and Unpack
+
+Download and unpack the NuttX tarball.  If you are reading this, then
+you have probably already done that.  After unpacking, you will end
+up with a directory called nuttx-version (where version is the NuttX
+version number). You might want to rename that directory nuttx to
+match the various instructions in the documentation and some scripts
+in the source tree.
+
+  * Download location:
+  
+    <https://nuttx.apache.org/download/>
+  
+  * Legacy download locations:
+
+    <https://bitbucket.org/nuttx/nuttx/downloads>  
+    <https://sourceforge.net/projects/nuttx/files/nuttx/>
+
+## Semi-Optional apps/ Package
+
+All NuttX libraries and example code used to be in included within
+the NuttX source tree.  As of NuttX-6.0, this application code was
+moved into a separate tarball, the apps tarball.  If you are just
+beginning with NuttX, then you will want to download the versioned
+apps tarball along with the NuttX tarball.  If you already have your
+own product application directory, then you may not need the apps
+tarball.
+
+It is called "Semi-optional" because if you don't have some `apps/`
+directory, NuttX will *fail* to build! You do not necessarily need
+to use the NuttX apps tarball but may, instead, provide your own
+custom application directory.  Such a custom directory would need
+to include a valid Makefile to support the build and a valid Kconfig
+file to support the configuration.  More about these files later.
+
+Download then unpack the apps tarball in the same directory where you
+unpacked the NuttX tarball.  After you unpack the apps tarball, you
+will have a new directory called apps-version (where the version
+should exactly match the version of the NuttX tarball).  Again, you
+might want to rename the directory to simply apps/ to match what
+you read in the documentation
+
+After unpacking (and renaming) the apps tarball, you will have two
+directories side by side like this:
+
+             |
+        +----+----+
+        |         |
+      nuttx/     apps/
+
+This is important because the NuttX build will expect to find the
+apps directory in that (default) location.  That default location
+can be changed by modifying your NuttX configuration file, but that
+is another story.
+
+## Installation Directories with Spaces in the Path
+
+The nuttx build directory should reside in a path that contains no
+spaces in any higher level directory name.  For example, under
+Cygwin, your home directory might be formed from your first and last
+names like: `/home/First Last`. That will cause strange errors when
+the make system tries to build.
+
+[Actually, that problem is probably not too difficult to fix.  Some
+ Makefiles probably just need some paths within double quotes]
+
+I work around spaces in the home directory name, by creating a
+new directory that does not contain any spaces, such as `/home/nuttx`.
+Then I install NuttX in `/home/nuttx` and always build from
+`/home/nuttx/nuttx-code`.
+
+## Downloading from Repositories
+
+### Cloning the Repository
+
+**BEFORE** cloning repositories on any Windows platform do the following GIT
+command:
+
+    git config --global core.autocrlf false
+
+That will avoid conversions of linefeeds (newlines, \n) to carriage
+return plus linefeed sequences (\r\n)
+
+The current NuttX du jour is available in from a GIT repository.  Here are
+instructions for cloning the core NuttX RTOS (corresponding to the nuttx
+tarball discussed above):
+
+    git clone https://gitbox.apache.org/repos/asf/incubator-nuttx.git nuttx
+
+-or-
+
+    git clone https://github.com/apache/incubator-nuttx.git nuttx
+
+And the semi-optional apps/ application directory and be cloned like:
+
+    git clone https://gitbox.apache.org/repos/asf/incubator-nuttx-apps.git apps
+  
+-or-
+  
+    git clone https://github.com/apache/incubator-nuttx-apps.git apps
+
+That will give you the same directory structure like this:
+    
+             |
+        +----+----+
+        |         |
+      nuttx/     apps/
+
+### Configuring the Clones
+
+The following steps need to be performed for each of the repositories.
+After changing to the clone directory:
+
+Set your identity:
+
+    git config --global user.name "My Name"
+    git config --global user.email my.name@example.com
+  
+Colorized diffs are much easier to read:
+
+    git config --global color.branch auto
+    git config --global color.diff auto
+    git config --global color.interactive auto
+    git config --global color.status auto
+
+Checkout other settings
+
+    git config --list
+
+### Cloning NuttX Inside Cygwin
+
+If you are cloning the NuttX repository, it is recommended to avoid
+automatic end of lines conversions by git. These conversions may break
+some scripts like configure.sh. Before cloning, do the following:
+
+    git config --global core.autocrlf false
+
+## Related Repositories
+
+These are standalone repositories:
+
+  * <https://gitbox.apache.org/repos/asf/incubator-nuttx-apps>  
+    or  
+    <https://github.com/apache/incubator-nuttx-apps.git>
+    
+    This directory holds an optional package of applications and libraries
+    can be used with the NuttX RTOS.  There is a README.txt file there that
+    will provide more information about that package.
+
+  * <https://bitbucket.org/nuttx/nxwidgets>
+  
+    This is the NuttX C++ graphics support.  This includes NxWM, the tiny
+    NuttX Window Manager.
+
+  * <https://bitbucket.org/nuttx/uclibc>
+  
+    This repository contains a version of the uClibc++ C++ library.  This code
+    originates from <http://cxx.uclibc.org/> and has been adapted for NuttX by the
+    RGMP team (<http://rgmp.sourceforge.net/wiki/index.php/Main_Page>).
+
+  * <https://bitbucket.org/nuttx/buildroot>
+  
+    A environment that you can to use to build a custom, NuttX GNU toolchain.
+
+  * <https://bitbucket.org/nuttx/tools>
+  
+    There are snapshots of some tools here that you will need to work with
+    NuttX:  kconfig-frontends, genromfs, and others.
+
+## Notes about Header Files
+
+### Other C-Library Header Files
+
+When a GCC toolchain is built, it must be built against a C library.
+The compiler together with the contents of the C library completes the
+C language definition and provides the complete C development
+environment.  NuttX provides its own, built-in C library.  So the
+complete, consistent C language definition for use with NuttX comes from
+the combination of the compiler and the header files provided by the
+NuttX C library.
+
+When a GCC toolchain is built, it incorporates the C library header
+files into the compiler internal directories and, in this way, the C
+library really becomes a part of the toolchain.  If you use the NuttX
+buildroot toolchain as described below under "NuttX Buildroot
+Toolchain", your GCC toolchain will build against the NuttX C library
+and will incorporate the NuttX C library header files as part of the
+toolchain.
+
+If you use some other, third-party tool chain, this will not be the
+case, however.  Those toolchains were probably built against some
+other, incompatible C library distribution (such as newlib).  Those
+tools will have incorporated the incompatible C library header files
+as part of the toolchain.  These incompatible header files must *not*
+be used with NuttX because they will conflict with definitions in the
+NuttX built-in C-Library.  For such toolchains that include header
+files from a foreign C-Library, NuttX must be compiled without using
+the standard header files that are distributed with your toolchain.
+This prevents including conflicting, incompatible header files such
+as stdio.h.
+
+The math.h and stdarg.h are probably the two most trouble some header
+files to deal with.  These troublesome header files are discussed in
+more detail below.
+
+### Header Files Provided by Your Toolchain
+
+Certain header files, such as `setjmp.h`, `stdarg.h`, and `math.h`, may still
+be needed from your toolchain and your compiler may not, however, be able
+to find these if you compile NuttX without using standard header files
+(i.e., with `-nostdinc`).  If that is the case, one solution is to copy
+those header file from your toolchain into the NuttX include directory.
+
+### Duplicated Header Files
+
+There are also a few header files that can be found in the `nuttx/include`
+directory which are duplicated by the header files from your toolchain.
+stdint.h and stdbool.h are examples.  If you prefer to use the `stdint.h`
+and `stdbool.h` header files from your toolchain, those could be copied
+into the `nuttx/include/` directory. Using most other header files from
+your toolchain would probably cause errors.
+
+### math.h
+
+Even though you should not use a foreign C-Library, you may still need
+to use other, external libraries with NuttX.  In particular, you may
+need to use the math library, libm.a.  NuttX supports a generic, built-in
+math library that can be enabled using `CONFIG_LIBM=y`.  However, you may
+still want to use a higher performance external math library that has
+been tuned for your CPU.  Sometimes such tuned math libraries are
+bundled with your toolchain.
+
+The math library header file, `math.h`, is a then special case.  If you do
+nothing, the standard math.h header file that is provided with your
+toolchain will be used.
+
+If you have a custom, architecture specific math.h header file, then
+that header file should be placed at `arch/<cpu>/include/math.h`.  There
+is a stub `math.h` header file located at `include/nuttx/lib/math.h`.  This stub
+header file can be used to "redirect" the inclusion to an architecture-
+specific math.h header file.  If you add an architecture specific math.h
+header file then you should also define `CONFIG_ARCH_MATH_H=y` in your
+NuttX Configuration file.  If `CONFIG_ARCH_MATH_H` is selected, then the
+top-level Makefile will copy the stub math.h header file from
+`include/nuttx/lib/math.h` to `include/math.h` where it will become the system
+`math.h` header file.  The stub `math.h` header file does nothing other
+than to include that architecture-specific `math.h` header file as the
+system `math.h` header file.
+
+### float.h
+
+If you enable the generic, built-in math library, then that math library
+will expect your toolchain to provide the standard `float.h` header file.
+The float.h header file defines the properties of your floating point
+implementation.  It would always be best to use your toolchain's `float.h`
+header file but if none is available, a default `float.h` header file will
+be provided if this option is selected.  However, there is no assurance
+that the settings in this `float.h` are actually correct for your platform!
+
+### stdarg.h
+
+In most cases, the correct version of stdarg.h is the version provided
+with your toolchain.  However, sometimes there are issues with
+using your toolchains `stdarg.h`.  For example, it may attempt to draw in
+header files that do not exist in NuttX or perhaps the header files that
+it uses are not compatible with the NuttX header files.  In those cases,
+you can use an architecture-specific `stdarg.h` header file by defining
+`CONFIG_ARCH_STDARG_H=y`.
+
+See the discussion above for the `math.h` header.  This setting works
+exactly the same for the `stdarg.h` header file.
+
+# CONFIGURING NUTTX
+
+## Instantiating "Canned" Configurations
+
+### `configure.sh` and `configure.bat`
+
+"Canned" NuttX configuration files are retained in:
+
+    boards/<arch-name>/<chip-name>/<board-name>/configs/<config-dir>
+
+Where `<board-name>` is the name of your development board and `<config-dir>`
+is the name of the sub-directory containing a specific configuration for
+that board. `<arch-name>` and `<chip-name>` refer to characteristics of the
+MCU used on the board: `<arch-name>` is the CPU architecture implemented
+by the MCU; `<chip-name>` identifies the MCU chip family.  Only a few
+steps are required to instantiate a NuttX configuration, but to make the
+configuration even easier there are scripts available in the tools/
+sub-directory combines those simple steps into one command.
+
+There is one tool for use with any Bash-like shell that does configuration
+steps.  It is used as follows:
+
+    tools/configure.sh <board-name>:<config-dir>
+
+There is an alternative Windows batch file that can be used in the windows
+native environment like:
+
+    tools\configure.bat <board-name>:<config-dir>
+
+And, to make sure that other platforms are supported, there is also a
+C program at tools/configure.c that can be compiled to establish the
+board configuration.
+
+See `tools/README.txt` for more information about these scripts.
+
+General information about configuring NuttX can be found in:
+
+    {TOPDIR}/boards/README.txt
+    {TOPDIR}/boards/<arch-name>/<chip-name>/<board-name>/README.txt
+
+### The Hidden Configuration Scripts:
+
+As mentioned above, there are only a few simple steps to instantiating a
+NuttX configuration.  Those steps are hidden by the configuration scripts
+but are summarized below:
+  
+  1. Copy Files
+  
+     Configuring NuttX requires only copying two files from the
+     `<config-dir>` to the directory where you installed NuttX (TOPDIR):
+  
+       * Copy `boards/<arch-name>/<chip-name>/<board-name>/configs/<config-dir>/Make.def` to `{TOPDIR}/Make.defs`
+    
+         OR
+    
+       * Copy `boards/<arch-name>/<chip-name>/<board-name>/scripts/Make.def`
+         to `{TOPDIR}/Make.defs`
+    
+         Make.defs describes the rules needed by your tool chain to compile
+         and link code.  You may need to modify this file to match the
+         specific needs of your toolchain.  NOTE that a configuration may
+         have its own unique Make.defs file in its configuration directory or
+         it may use a common Make.defs file for the board in the scripts/
+         directory.  The first takes precedence.
+    
+       * Copy `boards/<arch-name>/<chip-name>/<board-name>/configs/<config-dir>/defconfig` to `{TOPDIR}/.config`
+    
+         The defconfig file holds the actual build configuration.  This
+         file is included by all other make files to determine what is
+         included in the build and what is not.  This file is also used
+         to generate a C configuration header at `include/nuttx/config.h`.
+    
+       * Copy other, environment-specific files to `{TOPDIR}`
+    
+         This might include files like .gdbinit or IDE configuration files
+         like .project or .cproject.
+  
+  2. Refresh the Configuration
+  
+     New configuration setting may be added or removed.  Existing settings
+     may also change there values or options.  This must be handled by
+     refreshing the configuration as described below.
+    
+     NOTE:  NuttX uses only compressed defconfig files.  For the NuttX
+     defconfig files, this refreshing step is *NOT* optional; it is also
+     necessary to uncompress and regenerate the full making file.  This is
+     discussed further below.
+
+## Refreshing Configurations
+
+Configurations can get out of date.  As new configuration settings are
+added or removed or as dependencies between configuration settings
+change, the contents of a default configuration can become out of synch
+with the build systems.  Hence, it is a good practice to "refresh" each
+configuration after configuring and before making.  To refresh the
+configuration, use the NuttX Configuration Tool like this:
+
+    make oldconfig
+
+AFTER you have instantiated the NuttX configuration as described above.
+The configuration step copied the .config file into place in the top-level
+NuttX directory; 'make oldconfig' step will then operate on that .config
+file to bring it up-to-date.
+
+If your configuration is out of date, you will be prompted by 'make oldconfig'
+to resolve the issues detected by the configuration tool, that is, to
+provide values for the new configuration options in the build system.  Doing
+this can save you a lot of problems down the road due to obsolete settings in
+the default board configuration file.  The NuttX configuration tool is
+discussed in more detail in the following paragraph.
+
+Confused about what the correct value for a new configuration item should
+be?  Enter ? in response to the 'make oldconfig' prompt and it will show
+you the help text that goes with the option.
+
+If you don't want to make any decisions are willing to just accept the
+recommended default value for each new configuration item, an even easier
+way is:
+
+    make olddefconfig
+
+The olddefconfig target will simply bring your configuration up to date with
+the current Kconfig files, setting any new options to the default value.
+No questions asked.
+
+## NuttX Configuration Tool
+
+An automated tool has been incorporated to support re-configuration
+of NuttX.  This tool is based on the kconfig-frontends application available
+at <https://bitbucket.org/nuttx/tools/src/master/kconfig-frontends/>.  (This
+is a snapshot of the old <http://ymorin.is-a-geek.org/projects/kconfig-frontends>
+which is no longer available.)  This application provides a tool called
+`kconfig-mconf` that is used by the NuttX top-level Makefile. The following
+make target is provided:
+
+    make menuconfig
+
+This make target will bring up NuttX configuration menus.
+
+**WARNING**:  Never do `make menuconfig` on a configuration that has
+not been converted to use the kconfig-frontends tools!  This will
+damage your configuration (see
+<http://www.nuttx.org/doku.php?id=wiki:howtos:convertconfig>).
+
+How do we tell a new configuration from an old one? See "Incompatibilities
+with Older Configurations" below.
+
+The `menuconfig` make target depends on two things:
+
+  1. The Kconfig configuration data files that appear in almost all
+     NuttX directories.  These data files are the part that is still
+     under development (patches are welcome!).  The Kconfig files
+     contain configuration information for the configuration settings
+     relevant to the directory in which the Kconfig file resides.
+     
+     NOTE: For a description of the syntax of this configuration file,
+     see kconfig-language.txt in the tools repository at
+     <https://bitbucket.org/nuttx/tools>
+  
+  2. The `kconfig-mconf` tool. `kconfig-mconf` is part of the
+     kconfig-frontends package.  You can download that package from the
+     snapshot in the tools repository at <https://bitbucket.org/nuttx/tools>.
+  
+     Building kconfig-frontends under Linux may be as simple as
+     `configure; make; make install` but there may be some build
+     complexities, especially if you are building under Cygwin.  See
+     the more detailed build instructions in the top-level README.txt
+     file of the tools repository at <https://bitbucket.org/nuttx/tools>.
+  
+  
+     The `make install` step will, by default, install the `kconfig-mconf`
+     tool at `/usr/local/bin/mconf`.  Where ever you choose to
+     install `kconfig-mconf`, make certain that your PATH variable includes
+     a path to that installation directory.
+  
+     The kconfig-frontends tools will not build in a native Windows
+     environment directly "out-of-the-box".  For the Windows native
+     case, you can use the modified version of kconfig-frontends
+     that can be found at
+
+     <http://uvc.de/posts/linux-kernel-configuration-tool-kconfig-under-windows.html>  
+
+     or a more recent port that can be found at  
+
+     <http://reclonelabs.com/more-kconfig-awesomeness-for-windows/>.
+   
+The basic configuration order is "bottom-up":
+   
+   - Select the build environment,
+   - Select the processor,
+   - Select the board,
+   - Select the supported peripherals
+   - Configure the device drivers,
+   - Configure the application options on top of this.
+   
+This is pretty straight forward for creating new configurations
+but may be less intuitive for modifying existing configurations.
+
+Another ncurses-based tool that is an option to kconfig-mconf is
+kconfig-nconf.  The differences are primary in in the aesthetics of the
+UI.  If you have kconfig-nconf built, then you can invoke that front end
+with:
+   
+     make nconfig
+   
+If you have an environment that supports the Qt or GTK graphical systems
+(probably KDE or gnome, respectively, or Cygwin under Windows with Qt or
+GTK installed), then you can also build the graphical kconfig-frontends,
+kconfig-qconf and kconfig-gconf.  In these case, you can start the
+graphical configurator with either:
+   
+     make qconfig
+   
+ or
+   
+     make gconfig
+   
+Some keyboard shortcuts supported by kconfig-mconf, the tool that runs
+when you do 'make menuconfig':
+
+   - `?` will bring up the mconfig help display.
+   
+   - `/` can be used find configuration selections.
+   
+   - `Z` can be used to reveal hidden configuration options
+   
+These last two shortcuts are described further in the following
+paragraphs.
+
+## Finding Selections in the Configuration Menus
+
+The NuttX configuration options have gotten complex and it can be very
+difficult to find options in the menu trees if you are not sure where
+to look.  The "basic configuration order" describe above can help to
+narrow things down.
+
+But if you know exactly what configuration setting you want to select,
+say CONFIG_XYZ, but not where to find it, then the 'make menuconfig'
+version of the tool offers some help:  By pressing the '/' key, the
+tool will bring up a menu that will allow you to search for a
+configuration item.  Just enter the string CONFIG_XYZ and press 'ENTER'.
+It will show you not only where to find the configuration item, but
+also all of the dependencies related to the configuration item.
+
+## Reveal Hidden Configuration Options
+
+If you type `Z`, then kconfig-mconf will change what is displayed.
+Normally, only enabled features that have all of their dependencies met
+are displayed.  That is, of course, not very useful if you would like to
+discover new options or if you are looking for an option and do not
+realize that the dependencies have not yet been selected and, hence, it
+is not displayed.
+
+But if you enter `Z`, then every option will be shown, whether or not its
+dependencies have been met.  You can then see everything that could be
+selected with the right dependency selections.  These additional options
+will be shown the `-` for the selection and for the value (since it
+cannot be selected and has no value).  About all you do is to select
+the `<Help>` option to see what the dependencies are.
+
+## Make Sure that You are on the Right Platform
+
+Saved configurations may run on Linux, Cygwin (32- or 64-bit), or other
+platforms.  The platform characteristics can be changed use `make
+menuconfig`.  Sometimes this can be confusing due to the differences
+between the platforms.  Enter sethost.sh
+
+sethost.sh is a simple script that changes a configuration to your
+host platform.  This can greatly simplify life if you use many different
+configurations.  For example, if you are running on Linux and you
+configure like this:
+
+    tools/configure.sh board:configuration
+
+The you can use the following command to both (1) make sure that the
+configuration is up to date, AND (2) the configuration is set up
+correctly for Linux:
+
+    tools/sethost.sh -l
+
+Or, if you are on a Windows/Cygwin 64-bit platform:
+
+    tools/sethost.sh -c
+
+Or, for MSYS/MSYS2:
+
+    tools/sethost.sh -g
+
+Other options are available from the help option built into the
+script.  You can see all options with:
+
+    tools/sethost.sh -h
+
+Recently, the options to the configure.sh (and configure.bat) scripts have
+been extended so that you both setup the configuration, select for the host
+platform that you use, and uncompress and refresh the defconfig file all in
+one command like:
+
+    tools/configure.sh -l board:configuration
+
+For a Linux host or for a Windows/Cygwin host:
+
+    tools/configure.sh -c board:configuration
+
+Other options are available from the help option built into the
+script.  You can see all options with:
+
+    tools/configure.sh -h
+
+## Comparing Two Configurations
+
+If you try to compare two configurations using 'diff', you will probably
+not be happy with the result.  There are superfluous things added to
+the configuration files that make comparisons with the human eye
+difficult.
+
+There is a tool at nuttx/tools/cmpconfig.c that can be built to simplify
+these comparisons.  The output from this difference tool will show only
+the meaningful differences between two configuration files.  This tool is
+built as follows:
+
+    cd nuttx/tools
+    make -f Makefile.host
+
+This will create a program called 'cmpconfig' or 'comconfig.exe' on Windows.
+
+Why would you want to compare two configuration files?  Here are a few
+of the reasons why I do this
+
+  1. When I create a new configuration I usually base it on an older
+     configuration and I want to know, "What are the options that I need to
+     change to add the new feature to the older configurations?"  For example,
+     suppose that I have a boardA/nsh configuration and I want to create a
+     boardA/nxwm configuration.  Suppose I already have boardB/nsh and
+     boardB/nxwm configurations.  Then by comparing the boardB/nsh with the
+     boardB/nxwm I can see the modifications that I would need to make to my
+     boardA/nsh to create a new  boardA/nxwm.
+  
+  2. But the most common reason that I use the 'cmpconfig' program is to
+     check the results of "refreshing" a configuration with 'make oldconfig'
+     (see the paragraph "Refreshing Configurations" above).  The 'make
+     oldconfig' command will make changes to my configuration and using
+     'cmpconfig', I can see precisely what those changes were and if any
+     should be of concern to me.
+  
+  3. The 'cmpconfig' tool can also be useful when converting older, legacy
+     manual configurations to the current configurations based on the
+     kconfig-frontends tools.  See the following paragraph.
+
+## Making defconfig Files
+
+### .config Files as defconfig Files:
+
+The minimum defconfig file is simply the generated .config file with
+CONFIG_APPS_DIR setting removed or commented out.  That setting provides
+the name and location of the apps/ directory relative to the nuttx build
+directory.  The default is ../apps/, however, the apps directory may be
+any other location and may have a different name.  For example, the name
+of versioned NuttX releases are always in the form apps-xx.yy where xx.yy
+is the version number.
+
+### Finding the apps/ Directory Path:
+
+When the default configuration is installed using one of the scripts or
+programs in the NuttX tools directory, there will be an option to provide
+the path to the apps/ directory.  If not provided, then the configure tool
+will look around and try to make a reasonable decision about where the
+apps/ directory is located.
+
+### Compressed defconfig Files:
+
+The Makefile also supports an option to generate very small defconfig
+files.  The .config files are quite large and complex.  But most of the
+settings in the .config file simply have the default settings from the
+Kconfig files.  These .config files can be converted into small defconfig
+file:
+    
+    make savedefconfig
+    
+That make target will generate a defconfig file in the top-level
+directory.  The size reduction is really quite remarkable:
+    
+    wc -l .config defconfig
+     1085 .config
+       82 defconfig
+     1167 total
+    
+In order to be usable, the .config file installed from the compressed
+defconfig file must be reconstituted using:
+    
+    make olddefconfig
+    
+  > **NOTE 1**:  Only compressed defconfig files are retained in the NuttX repository.
+  > All patches and PRs that attempt to add or modify a defconfig file MUST
+  > use the compressed defconfig format as created by 'make savdefconfig.'
+    
+  > **NOTE 2**:  When 'make savedefconfig' runs it will try several things some of
+  > which are expected to fail.  In these cases you will see an error message
+  > from make followed by "(ignored)."  You should also ignore these messages
+    
+**CAUTION**:  This size reduction was accomplished by removing all setting
+from the .config file that were at the default value.  'make olddefconfig'
+can regenerate the original .config file by simply restoring those default
+settings.  The underlying assumption here is, of course, that the default
+settings do not change.  If the default settings change, and they often
+do, then the original .config may not be reproducible.
+
+So if your project requires 100% reproducibility over a long period of
+time, you make want to save the complete .config files vs. the standard,
+compressed defconfig file.
+
+### Configuring with "Compressed" defconfig Files:
+
+As described above defconfig, all NuttX defconfig files are compressed
+using 'make savedeconfig'.  These compressed defconfig files are
+generally not fully usable as they are and may not build the target
+binaries that you want because the compression process removed all of
+the default settings from the defconfig file.  To restore the default
+settings, you should run the following after configuring:
+
+    make olddefconfig
+
+That will restore the the missing defaulted values.
+
+Using this command after configuring is generally a good practice anyway:
+Even if the defconfig files are not "compressed" in this fashion, the
+defconfig file may be old and the only way to assure that the installed
+.config is is up to date is via 'make oldconfig' or 'make olddefconfig'.
+See the paragraph above entitled ""Refreshing Configurations" for
+additional information.
+
+## Incompatibilities with Older Configurations
+
+**WARNING**
+
+The current NuttX build system supports *only* the new compressed,
+defconfig configuration files generated using the kconfig-frontends tools
+as described in the preceding section.  Support for the older, legacy,
+manual configurations was eliminated in NuttX 7.0; support for
+uncompressed .config-files-as-defconfig files was eliminated after
+NuttX-7.21.  All configurations must now be done using the
+kconfig-frontends tool.  The older manual configurations and the new
+kconfig-frontends configurations are not compatible.  Old legacy
+configurations can *not* be used with the kconfig-frontends tool and,
+hence, cannot be used with releases of NuttX 7.0 and beyond:
+
+If you run 'make menuconfig' with a legacy configuration the resulting
+configuration will probably not be functional.
+
+  > Q: How can I tell if a configuration is a new kconfig-frontends
+  >   configuration or an older, manual configuration?
+  >
+  > A: Only old, manual configurations will have an appconfig file
+  > 
+  > Q: How can I convert a older, manual configuration into a new,
+  >    kconfig-frontends toolchain.
+  >
+  > A: Refer to <http://www.nuttx.org/doku.php?id=wiki:howtos:convertconfig>
+  
+**WARNING**
+
+As described above, whenever you use a configuration, you really should
+always refresh the configuration with the following command *before* you
+make NuttX:
+
+    make oldconfig
+
+OR
+
+    make olddefconfig
+
+This will make sure that the configuration is up-to-date in the event that
+it has lapsed behind the current NuttX development (see the paragraph
+"Refreshing Configurations" above).  But this only works with *new*
+configuration files created with the kconfig-frontends tools.
+
+Further, this step is *NOT* optional with the new, compressed defconfig
+files.  It is a necessary step that will also uncompress the defconfig
+file, regenerating the .config and making it usable for NuttX builds.
+
+Never do `make oldconfig` (OR `make menuconfig`) on a  configuration that
+has not been converted to use the kconfig-frontends tools!  This will
+damage your configuration (see
+<http://www.nuttx.org/doku.php?id=wiki:howtos:convertconfig>).
+
+## NuttX Configuration Tool under DOS
+
+  Recent versions of NuttX support building NuttX from a native Windows
+  console window (see *Native Windows Build* below).  But kconfig-frontends
+  is a Linux tool.  At one time this was a problem for Windows users, but
+  now there are two specially modified versions of the kconfig-frontends
+  tools that can be used.  One can be found here:
+  <http://uvc.de/posts/linux-kernel-configuration-tool-kconfig-under-windows.html>
+
+  The configuration steps of the most recent versions of NuttX require the
+  kconfig-tweak tool that is not not available in the the above.  However,
+  there has been an update to this Kconfig Windows tools that does include
+  kconfig-tweak:  http://reclonelabs.com/more-kconfig-awesomeness-for-windows/
+
+  Source code is available here: <https://github.com/reclone/kconfig-frontends-win32>
+  and <https://github.com/reclone/kconfig-frontends-win32/releases>
+
+  It is also possible to use the version of kconfig-frontends built
+  under Cygwin outside of the Cygwin "sandbox" in a native Windows
+  environment:
+
+  1. You can run the configuration tool using Cygwin.  However, the
+     Cygwin Makefile.win will complain so to do this will, you have
+     to manually edit the .config file:
+     
+     a. Delete the line: CONFIG_WINDOWS_NATIVE=y
+     
+     b. Change the apps/ directory path, CONFIG_APPS_DIR to use Unix
+      
+        style delimiters.  For example, change "..\apps" to "../apps"
+     
+     And of course, after you use the configuration tool you need to
+     restore CONFIG_WINDOWS_NATIVE=y and the correct CONFIG_APPS_DIR.
+
+  2. You can, with some effort, run the Cygwin kconfig-mconf tool
+     directly in the Windows console window.  In this case, you do not
+     have to modify the .config file, but there are other complexities:
+     
+    a. You need to temporarily set the Cygwin directories in the PATH
+       variable then run kconfig-mconf manually like:
+         
+          kconfig-mconf Kconfig
+         
+       There is a Windows batch file at tools/kconfig.bat that automates
+       these steps:
+         
+         tools/kconfig menuconfig
+     
+    b. There is an issue with accessing DOS environment variables from
+       the Cygwin kconfig-mconf running in the Windows console.  The
+       following change to the top-level Kconfig file seems to work
+       around these problems:
+     
+          config APPSDIR
+              string
+          -   option env="APPSDIR"
+          +   default "../apps"
+
+# TOOLCHAINS
+
+## Cross-Development Toolchains
+
+  In order to build NuttX for your board, you will have to obtain a cross-
+  compiler to generate code for your target CPU.  For each board,
+  configuration, there is a README.txt file (at
+  `boards/<arch-name>/<chip-name>/<board-name>/README.txt`).
+  That README file contains suggestions and information about appropriate
+  tools and development environments for use with your board.
+
+  In any case, the PATH environment variable will need to be updated to
+  include the location where the build can find the toolchain binaries.
+
+## NuttX Buildroot Toolchain
+
+  For many configurations, a DIY set of tools is available for NuttX.  These
+  tools can be downloaded from the NuttX Bitbucket.org file repository.  After
+  unpacking the buildroot tarball, you can find instructions for building
+  the tools in the `buildroot/boards/README.txt` file.
+
+  Check the README.txt file in the configuration directory for your board
+  to see if you can use the buildroot toolchain with your board (this
+  README.txt file is located in
+  `boards/<arch-name>/<chip-name>/<board-name>/README.txt`).
+
+  This toolchain is available for both the Linux and Cygwin development
+  environments.
+
+  Advantages:  (1) NuttX header files are built into the tool chain,
+  and (2) related support tools like NXFLAT tools, the ROMFS
+  genromfs tools, and the kconfig-frontends tools can be built into your
+  toolchain.
+
+  Disadvantages:  This tool chain is not was well supported as some other
+  toolchains.  GNU tools are not my priority and so the buildroot tools
+  often get behind.  For example, until recently there was no EABI support
+  in the NuttX buildroot toolchain for ARM.
+
+  NOTE: For Cortex-M3/4, there are OABI and EABI versions of the buildroot
+  toolchains.  If you are using the older OABI toolchain the prefix for
+  the tools will be arm-nuttx-elf-; for the EABI toolchain the prefix will
+  be arm-nuttx-eabi-.  If you are using the older OABI toolchain with
+  an ARM Cortex-M3/4, you will need to set CONFIG_ARMV7M_OABI_TOOLCHAIN
+  in the .config file in order to pick the right tool prefix.
+
+  If the make system ever picks the wrong prefix for your toolchain, you
+  can always specify the prefix on the command to override the default
+  like:
+
+    make CROSSDEV=arm-nuttx-elf
+
+# SHELLS
+
+The NuttX build relies on some shell scripts.  Some are inline in the
+Makefiles and many are executable scripts in the tools/. directory.  The
+scripts were all developed using bash and many contain bash shell
+dependencies.
+
+Most of the scripts begin with #!/bin/bash to specifically select the
+bash shell.  Some still have #!/bin/sh but I haven't heard any complaints
+so these must not have bash dependencies.
+
+There are two shell issues that I have heard of:
+
+  1. Linux where /bin/sh refers to an incompatible shell (like ksh or csh).
+     
+     In this case, bash is probably available and the #!/bin/bash at the
+     beginning of the file should do the job.  If any scripts with #!/bin/sh
+     fail, try changing that to #!/bin/bash and let me know about the change.
+  
+  2. FreeBSD with the Bourne Shell and no bash shell.
+     
+     The other, reverse case has also been reported on FreeBSD setups that
+     have the Bourne shell, but not bash.  In this base, `#!/bin/bash` fails
+     but `#!/bin/sh` works okay.  My recommendation in this case is to create
+     a symbolic link at `/bin/bash` that refers to the Bourne shell.
+     
+     There may still be issues, however, with certain the bash-centric scripts
+     that will require modifications.
+  
+# BUILDING NUTTX
+
+## Building
+
+NuttX builds in-place in the source tree.  You do not need to create
+any special build directories.  Assuming that your Make.defs is setup
+properly for your tool chain and that PATH environment variable contains
+the path to where your cross-development tools are installed, the
+following steps are all that are required to build NuttX:
+
+    cd {TOPDIR}
+    make
+
+At least one configuration (eagle100) requires additional command line
+arguments on the make command.  Read
+`{TOPDIR}/boards/<arch-name>/<chip-name>/<board-name>/README.txt` to see
+if that applies to your target.
+
+## Re-building
+
+Re-building is normally simple -- just type make again.
+
+But there are some things that can "get you" when you use the Cygwin
+development environment with Windows native tools.  The native Windows
+tools do not understand Cygwin's symbolic links, so the NuttX make system
+does something weird:  It copies the configuration directories instead of
+linking to them (it could, perhaps, use the NTFS 'mklink' command, but it
+doesn't).
+
+A consequence of this is that you can easily get confused when you edit
+a file in one of the linked (i.e., copied) directories, re-build NuttX,
+and then not see your changes when you run the program.  That is because
+build is still using the version of the file in the copied directory, not
+your modified file!
+
+Older versions of NuttX did not support dependencies in this
+configuration.  So a simple work around this annoying behavior in this
+case was the following when you re-build:
+
+     make clean_context all
+
+This 'make' command will remove of the copied directories, re-copy them,
+then make NuttX.
+
+However, more recent versions of NuttX do support dependencies for the
+Cygwin build.  As a result, the above command will cause everything to be
+rebuilt (because it removes and will cause recreating the
+include/nuttx/config.h header file).  A much less gracefully but still
+effective command in this case is the following for the ARM configuration:
+
+    rm -rf arch/arm/src/chip arch/arm/src/board
+
+This "kludge" simple removes the copied directories.  These directories
+will be re-created when you do a normal 'make' and your edits will then be
+effective.
+
+## Build Targets and Options
+
+### Build Targets
+
+Below is a summary of the build targets available in the top-level
+NuttX Makefile:
+
+  * `all`
+
+    The default target builds the NuttX executable in the selected output
+    formats.
+
+  * `clean`
+
+    Removes derived object files, archives, executables, and temporary
+    files, but retains the configuration and context files and directories.
+
+  * `distclean`
+
+    Does 'clean' then also removes all configuration and context files.
+    This essentially restores the directory structure to its original,
+    unconfigured stated.
+
+Application housekeeping targets.  The APPDIR variable refers to the user
+application directory.  A sample apps/ directory is included with NuttX,
+however, this is not treated as part of NuttX and may be replaced with a
+different application directory.  For the most part, the application
+directory is treated like any other build directory in the Makefile script.
+However, as a convenience, the following targets are included to support
+housekeeping functions in the user application directory from the NuttX
+build directory.
+
+  * `apps_clean`
+
+    Perform the clean operation only in the user application directory
+
+  * `apps_distclean`
+
+    Perform the distclean operation only in the user application directory.
+    The apps/.config file is preserved so that this is not a "full" distclean
+    but more of a configuration "reset" for the application directory.
+
+  * `export`
+
+    The export target will package the NuttX libraries and header files into
+    an exportable package.  Caveats: (1) These needs some extension for the KERNEL
+    build. (2) The logic in tools/mkexport.sh only supports GCC and, for example,
+    explicitly assumes that the archiver is 'ar'
+
+  * `download`
+
+    This is a helper target that will rebuild NuttX and download it to the target
+    system in one step.  The operation of this target depends completely upon
+    implementation of the DOWNLOAD command in the user Make.defs file.  It will
+    generate an error an error if the DOWNLOAD command is not defined.
+
+The following targets are used internally by the make logic but can be invoked
+from the command under certain conditions if necessary.
+
+  * `depend`
+
+    Create build dependencies. (NOTE:  There is currently no support for build
+    dependencies under Cygwin using Windows-native toolchains.)
+
+  * `context`
+
+    The context target is invoked on each target build to assure that NuttX is
+    properly configured.  The basic configuration steps include creation of the
+    the config.h and version.h header files in the include/nuttx directory and
+    the establishment of symbolic links to configured directories.
+
+  * `clean_context`
+
+    This is part of the distclean target.  It removes all of the header files
+    and symbolic links created by the context target.
+
+### Build Options
+
+Of course, the value any make variable an be overridden from the make command
+line.  However, there is one particular variable assignment option that may
+be useful to you:
+
+  * `V=1`
+
+    This is the build "verbosity flag."  If you specify V=1 on the make command
+    line, you will see the exact commands used in the build. This can be very
+    useful when adding new boards or tracking down compile time errors and
+    warnings (Contributed by Richard Cochran).
+
+## Native Windows Build
+
+The beginnings of a Windows native build are in place but still not often
+used as of this writing.  The build was functional but because of lack of
+use may find some issues to be resolved with this build configuration.
+
+The windows native build logic initiated if CONFIG_WINDOWS_NATIVE=y is
+defined in the NuttX configuration file:
+
+This build:
+
+  - Uses all Windows style paths
+  - Uses primarily Windows batch commands from cmd.exe, with
+  - A few extensions from GNUWin32
+
+In this build, you cannot use a Cygwin or MSYS shell. Rather the build must
+be performed in a Windows console window. Here is a better terminal than the
+standard issue, CMD.exe terminal:  ConEmu which can be downloaded from:
+<https://sourceforge.net/projects/conemu/> or <https://conemu.github.io/>.
+
+Build Tools.  The build still relies on some Unix-like commands.  I use
+the GNUWin32 tools that can be downloaded from <http://gnuwin32.sourceforge.net/>
+using the *Download all* selection.  Individual packages can be download
+instead if you know what you are doing and want a faster download (No, I
+can't tell you which packages you should or should not download).
+
+NOTE:  It should be possible to use Cygwin or MSYS2 in place of the GNUWin32
+tools.  There are, however, complexities in doing that because those tools
+depend on the shell environment and use DLLs that are not found (at least
+not without the correct setup).
+
+Host Compiler:  I use the MingGW GCC compiler which can be downloaded from
+<http://www.mingw.org/>.  If you are using GNUWin32, then it is recommended
+the you not install the optional MSYS components as there may be conflicts.
+
+Kconfig-frontends:  See the section entitled "NuttX Configuration Tool
+under DOS" for information about installing the kconfig-frontend tools to
+run natively under Windows.
+
+This capability should still be considered a work in progress because:
+
+  1. It has not been verified on all targets and tools, and
+  2. it still lacks some of the creature-comforts of the more mature
+     environments.
+
+## Installing GNUWin32
+
+  The Windows native build will depend upon a few Unix-like tools that can be
+  provided either by MSYS or GNUWin32.  The GNUWin32 are available from
+  <http://gnuwin32.sourceforge.net/>.  GNUWin32 provides ports of tools with a
+  GPL or similar open source license to modern MS-Windows (Microsoft Windows
+  2000 / XP / 2003 / Vista / 2008 / 7).  See
+  <http://gnuwin32.sourceforge.net/packages.html> for a list of all of the tools
+  available in the GNUWin32 package.
+
+  The SourceForge project is located here:
+  <http://sourceforge.net/projects/gnuwin32/>.  The project is still being
+  actively supported (although some of the Windows ports have gotten very old).
+
+  Some commercial toolchains include a subset of the GNUWin32 tools in the
+  installation.  My recommendation is that you download the GNUWin32 tools
+  directly from the sourceforge.net website so that you will know what you are
+  using and can reproduce your build environment.
+
+  GNUWin32 Installation Steps:
+
+  The following steps will download and execute the GNUWin32 installer.
+
+1. Download `GetGNUWin32-x.x.x.exe` from
+   <http://sourceforge.net/projects/getgnuwin32/files/>.  This is the
+   installer.  The current version as of this writing is 0.6.3.
+
+2. Run the installer.
+
+3. Accept the license.
+
+4. Select the installation directory.  My recommendation is the
+   directory that contains this README file (`<this-directory>`).
+
+5. After running `GetGNUWin32-0.x.x.exe`, you will have a new directory
+   `<this-directory>/GetGNUWin32`
+   
+   Note that the GNUWin32 installer didn't install GNUWin32.  Instead, it
+   installed another, smarter downloader.  That downloader is the GNUWin32
+   package management tool developed by the Open SSL project.
+   
+   The following steps probably should be performed from inside a DOS shell.
+
+6. Change to the directory created by `GetGNUWin32-x.x.x.exe`
+   
+      cd GetGNUWin32
+
+7. Execute the download.bat script.  The download.bat script will download
+   about 446 packages!  Enough to have a very complete Linux-like environment
+   under the DOS shell.  This will take awhile.  This step only downloads
+   the packages and the next step will install the packages.
+
+      download
+
+8. This step will install the downloaded packages.  The argument of the
+   install.bat script is the installation location.  C:\gnuwin32 is the
+   standard install location:
+   
+     install C:\gnuwin32
+   
+  **NOTE**:  This installation step will install *all* GNUWin32 packages... far
+  more than you will ever need.  If disc space is a problem for you, you might
+  need to perform a manual installation of the individual ZIP files that you
+  will find in the `<this directory>/GetGNUWin32/packages` directory.
+
+9. Make sure that you add the GNUWin32 tools to your path variable:
+   
+         set PATH=C:\gnuwin32\bin;%PATH%
+   
+  **WARNING**:  Make sure you have `C:\MinGW\bin` in your path before any other
+  directory that contains `libiconv-2.dll`. Apparently the `as.exe` in some
+  MinGW distributions are dependent on that DLL, and having an old
+  version of it in the path somewhere (for example GnuWin32 tools) will
+  cause as.exe to pick up the older version that doesn't have the entry
+  point it's looking for.
+
+# CYGWIN BUILD PROBLEMS
+
+## Performance
+
+Build performance under Cygwin is really not so bad, certainly not as good
+as a Linux build.  However, often you will find that the performance is
+not just bad but terrible.  If you are seeing awful performance.. like two
+or three compilations per second.. the culprit is usually your Windows
+Anti-Virus protection interfering with the build tool program execution.
+
+I use Cygwin quite often and I use Windows Defender.  In order to get good
+build performance, I routinely keep the Windows Defender "Virus & Threat
+Protections Settings" screen up:  I disable "Real-Time Protection" just
+before entering 'make' then turn "Real-Time Protection" back on when the
+build completes.  With this additional nuisance step, I find that build
+performance under Cygwin is completely acceptable.
+
+## Strange Path Problems
+
+If you see strange behavior when building under Cygwin then you may have
+a problem with your PATH variable.  For example, if you see failures to
+locate files that are clearly present, that may mean that you are using
+the wrong version of a tool.  For example, you may not be using Cygwin's
+'make' program at /usr/bin/make.  Try:
+
+    which make
+    /usr/bin/make
+
+When you install some toolchains (such as Yargarto or CodeSourcery tools),
+they may modify your PATH variable to include a path to their binaries.
+At that location, they may have GNUWin32 versions of the tools.  So you
+might actually be using a version of make that does not understand Cygwin
+paths.
+
+The solution is either:
+
+  1. Edit your PATH to remove the path to the GNUWin32 tools, or
+  
+  2. Put /usr/local/bin, /usr/bin, and /bin at the front of your path:
+     
+         export PATH=/usr/local/bin:/usr/bin:/bin:$PATH
+  
+## Window Native Toolchain Issues
+
+There are many popular Windows native toolchains that may be used with NuttX.
+Examples include CodeSourcery (for Windows), devkitARM, and several vendor-
+provided toolchains.  There are several limitations with using a and Windows
+based toolchain in a Cygwin environment.  The three biggest are:
+
+  1. The Windows toolchain cannot follow Cygwin paths.  Path conversions are
+     performed automatically in the Cygwin makefiles using the 'cygpath' utility
+     but you might easily find some new path problems.  If so, check out 'cygpath -w'
+  
+  2. Windows toolchains cannot follow Cygwin symbolic links.  Many symbolic links
+     are used in Nuttx (e.g., include/arch).  The make system works around these
+     problems for the Windows tools by copying directories instead of linking them.
+     But this can also cause some confusion for you:  For example, you may edit
+     a file in a "linked" directory and find that your changes had no effect.
+     That is because you are building the copy of the file in the "fake" symbolic
+     directory.  If you use a Windows toolchain, you should get in the habit of
+     making like this:
+     
+         make clean_context all
+     
+     An alias in your .bashrc file might make that less painful.  The rebuild
+     is not a long as you might think because there is no dependency checking
+     if you are using a native Windows toolchain.  That bring us to #3:
+
+## General Pre-built Toolchain Issues
+
+To continue with the list of "Window Native Toolchain Issues" we can add
+the following.  These, however, are really just issues that you will have
+if you use any pre-built toolchain (vs. building the NuttX toolchain from
+the NuttX buildroot package):
+
+There may be incompatibilities with header files, libraries, and compiler
+built-in functions detailed below.  For the most part, these issues
+are handled in the existing make logic.  But if you are breaking new ground,
+then you may encounter these:
+
+  1. Header Files.  Most pre-built toolchains will build with a foreign C
+     library (usually newlib, but maybe uClibc or glibc if you are using a
+     Linux toolchain).  This means that the header files from the foreign
+     C library will be built into the toolchain.  So if you "include <stdio.h>",
+     you will get the stdio.h from the incompatible, foreign C library and
+     not the nuttx stdio.h (at nuttx/include/stdio.h) that you wanted.
+     
+     This can cause confusion in the builds and you must always be
+     sure the -nostdinc is included in the CFLAGS.  That will assure that

Review comment:
       ```suggestion
        sure the `-nostdinc` is included in the `CFLAGS`.  That will assure that
   ```




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