[GitHub] [nuttx] lupyuen commented on pull request #9098: arm64: Updating ARCH_EARLY_PRINT support

["lupyuen (via GitHub)" <gi...@apache.org>]

lupyuen commented on PR #9098:
URL: https://github.com/apache/nuttx/pull/9098#issuecomment-1541203164

   Hi @qinwei2004: Allwinner A64 System Logging has a problem with Dropped Output, wonder if I can help to fix this problem in my upcoming PR...
   
   I'm now calling the System Log in my Allwinner A64 Bringup:
   
   ```text
   _info("Configure STATUS (PH9) for Input\n");
   _info("Status=%d\n", ...);
   _info("Configure PWR_BAT (PL7) for Output\n");
   _info("Set PWR_BAT (PL7) to High\n");
   _info("Status=%d\n", ...);
   ```
   
   [(Source)](https://github.com/lupyuen2/wip-pinephone-nuttx/blob/uart2/boards/arm64/a64/pinephone/src/pinephone_bringup.c#L208-L347)
   
   Previously the System Log appeared OK:
   
   ```text
   pinephone_modem_init: Configure STATUS (PH9) for Input
   pinephone_modem_init: Status=0
   pinephone_modem_init: Configure PWR_BAT (PL7) for Output
   pinephone_modem_init: Set PWR_BAT (PL7) to High
   pinephone_modem_init: Status=1
   ```
   
   [(Source)](https://gist.github.com/lupyuen/c6630b0a6e1616aada546143552fb113/0ffe0f16e9ad40082260544c00d6f6e4b2785cc9#file-uart-test-modem-log-L40-L74)
   
   But with the [recent update to `a64_serial.c`](https://github.com/apache/nuttx/commit/2eac660ff68a805cfcb02ca108b1e6cdac0f7d4e#diff-345b8952b508d50e2f214f8ba7b090cf826ad455aa3d175ed739f69eadf55fb0), the System Log now appears garbled with Dropped Output:
   
   ```text
   pinephone_modem_init: Configure STATUS (PH9) for Input
   pinephoneapinephone_modem_init: Status=1
   pinephone_modem_init: Configure Ppinephone_modem_init: Status=1
   ```
   
   [(Source)](https://gist.github.com/lupyuen/c6630b0a6e1616aada546143552fb113/f4b337c7bef9f5b69f208a753d8120bf2c57e322#file-uart-test-modem-log-L40-L46)
   
   I traced the Dropped Output to this modification:
   
   __Previously:__ `up_putc` calls `arm64_lowputc` to print the output:
   
   ```c
   int up_putc(int ch) {
     // arm64_lowputc waits for UART Ready before printing
     arm64_lowputc((uint8_t)ch);
   ```
   
   [(Source)](https://github.com/apache/nuttx/blob/e3f0f86514126afaf3726e330fbe5fd525ac9f09/arch/arm64/src/a64/a64_serial.c#L701-L714)
   
   And [`arm64_lowputc`](https://github.com/apache/nuttx/blob/2eac660ff68a805cfcb02ca108b1e6cdac0f7d4e/arch/arm64/src/a64/a64_lowputc.S#L86-L91) waits for UART Ready before wrting the output.
   
   __Now:__ `up_putc` calls `a64_uart_send` to print the output:
   
   ```c
   int up_putc(int ch) {
     // a64_uart_send doesn't wait for UART Ready before printing
     a64_uart_send(dev, ch);
   ```
   
   [(Source)](https://github.com/apache/nuttx/blob/2eac660ff68a805cfcb02ca108b1e6cdac0f7d4e/arch/arm64/src/a64/a64_serial.c#L635-L652)
   
   But [`a64_uart_send`](https://github.com/apache/nuttx/blob/2eac660ff68a805cfcb02ca108b1e6cdac0f7d4e/arch/arm64/src/a64/a64_serial.c#L424-L432) doesn't wait for UART Ready. That's why it drops the output.
   
   I can help to fix this, inside my upcoming PR for `a64_serial.c`:
   
   -   [Upcoming PR: Add support for Multiple UART Ports](https://github.com/lupyuen2/wip-pinephone-nuttx/pull/29)
   
   I will fix the Dropped Output by waiting for UART Ready, like this:
   
   ```c
   int up_putc(int ch) {
     // Wait for UART Ready
     while (!a64_uart_txready(dev)) {}
   
     // UART is now ready, OK to print
     a64_uart_send(dev, ch);
   ```
   
   [(`a64_uart_txready` is defined here)](https://github.com/apache/nuttx/blob/2eac660ff68a805cfcb02ca108b1e6cdac0f7d4e/arch/arm64/src/a64/a64_serial.c#L484-L492)
   
   Could you clarify if I understood the problem correctly?
   
   If you're OK, I shall fix this in my upcoming PR. Thanks :-)
   


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