[incubator-nuttx] branch master updated: stm32: lowputc: Ensure USART is disabled before configuring

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davids5 pushed a commit to branch master
in repository https://gitbox.apache.org/repos/asf/incubator-nuttx.git


The following commit(s) were added to refs/heads/master by this push:
     new e67f72b  stm32: lowputc: Ensure USART is disabled before configuring
e67f72b is described below

commit e67f72b02ddf3915a59997e8942ae8ba4b815d89
Author: Nathan Hartman <59...@users.noreply.github.com>
AuthorDate: Fri Sep 4 17:33:06 2020 -0400

    stm32: lowputc: Ensure USART is disabled before configuring
    
    arch/arm/src/stm32/stm32_lowputc.c:
    
        * stm32_lowsetup(): Ensure the USART is disabled before attempting
          to configure it because some register bits cannot be modified
          otherwise. This solves an issue that was encountered when a
          serial bootloader did not perform a full teardown/cleanup before
          launching NuttX.
---
 arch/arm/src/stm32/stm32_lowputc.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/arch/arm/src/stm32/stm32_lowputc.c b/arch/arm/src/stm32/stm32_lowputc.c
index e070c3f..9f67bcc 100644
--- a/arch/arm/src/stm32/stm32_lowputc.c
+++ b/arch/arm/src/stm32/stm32_lowputc.c
@@ -614,6 +614,18 @@ void stm32_lowsetup(void)
   /* Enable and configure the selected console device */
 
 #if defined(HAVE_CONSOLE) && !defined(CONFIG_SUPPRESS_UART_CONFIG)
+  /* Ensure the USART is disabled because some bits of the following
+   * registers cannot be modified otherwise.
+   *
+   * Although the USART is expected to be disabled at power on reset, this
+   * might not be the case if we boot from a serial bootloader that does not
+   * clean up properly.
+   */
+
+  cr  = getreg32(STM32_CONSOLE_BASE + STM32_USART_CR1_OFFSET);
+  cr &= ~USART_CR1_UE;
+  putreg32(cr, STM32_CONSOLE_BASE + STM32_USART_CR1_OFFSET);
+
   /* Configure CR2 */
 
   cr  = getreg32(STM32_CONSOLE_BASE + STM32_USART_CR2_OFFSET);