[GitHub] [incubator-nuttx] tidklaas commented on a change in pull request #2343: serial: Prevent RX stall

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

tidklaas commented on a change in pull request #2343:
URL: https://github.com/apache/incubator-nuttx/pull/2343#discussion_r526879103



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File path: drivers/serial/serial.c
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@@ -924,6 +924,20 @@ static ssize_t uart_read(FAR struct file *filep, FAR char *buffer, size_t buflen
               /* Re-enable UART Rx interrupts */
 
               uart_enablerxint(dev);
+
+              /* Check again if the RX buffer is empty.  The UART driver

Review comment:
       `uart_disablerxint()` is called in line 898. For cdcacm this just sets a flag that will prevent it from copying data into the RX buffer, but it will still accept new data from the USB layer and put it into its completion queue. So if a USB packet arrives between `uart_disablerxint()` at line 898 and `enter_critical_section()` at line 922, there will be data waiting in cdcacm's queue. When `uart_enablerxint()` is called at line 926, [cdcuart_rxint](https://github.com/apache/incubator-nuttx/blob/6ee7fdf874d802f7853db1f7a382b6e4bce708fb/drivers/usbdev/cdcacm.c#L2582) will call [cdcacm_release_rxpending](https://github.com/apache/incubator-nuttx/blob/6ee7fdf874d802f7853db1f7a382b6e4bce708fb/drivers/usbdev/cdcacm.c#L667), which will copy the queued data unto the RX buffer.




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