[GitHub] [incubator-nuttx] Ouss4 commented on pull request #4437: stm32_serial.c: Don't fake a TX interrupt when interrupts are not suppressed

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Ouss4 commented on pull request #4437:
URL: https://github.com/apache/incubator-nuttx/pull/4437#issuecomment-910189575


   Thanks for these details @davids5.
   I didn't attach an LA to look at what's going on with HW flow control enabled either (my stuff are kind of a mess right now), I might do that later.  However I tried to find when this was introduced and try to find any hint in the commit message or the change itself.  It came as part of https://github.com/apache/incubator-nuttx/commit/4494689a2220501f74404e68b3eb72c112c9a888#diff-867b440e179e185b86ca1b3423ad19b5174ec9345a02380733d51f437a40db58R691-R700
   
   Since everything is folded, let me copy the relevant snippet:
   
   ```C
   #ifndef CONFIG_SUPPRESS_SERIAL_INTS
   //      priv->im |= ;
         up_serialout(priv, stm32_USART_IM_OFFSET, priv->im);
   
         /* Fake a TX interrupt here by just calling uart_xmitchars() with
          * interrupts disabled (note that the may recurse and that priv->im
          * may be altered.
          */
   
         uart_xmitchars(dev);
   #endif
   ```
   My guess is since setting the interrupt bits was commented out, faking it was necessary.
   This was completed in https://github.com/apache/incubator-nuttx/commit/a7942e1bbe734f9bd7a4b737a899fa880ef66a88, but (again my guess) faking the interrupt part was not removed (i.e. adding an `"#else` was forgotten).  At that point flow control was not implemented in STM32.
   I don't know if later this part was deemed necessary when flow control was added.


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