Messages in this thread | | | From | "Bollinger, Seth" <> | Subject | Possible software flow problem in serial_core | Date | Thu, 20 Mar 2014 13:44:57 +0000 |
| |
Hello All,
We’ve recently run into a possible problem with software flow control handling in the serial_core layer.
Here is the scenario:
1. Transmit from uart to remote device 2. Remote device sends us an XOFF 3. The tty layer receives the XOFF 4. stop_tty() - The uart transmitter is stopped (ops->stop_tx) just as the serial_core ring is cleared (this could trap a few bytes in the fifo). 5. Remote device sends us an XON 6. The tty layer receives the XON 7. start_tty() - However, the serial_core ring is empty, so the call to start the uart transmitter (uart_start:ops->start_tx) is skipped
Any window, however small, could leave bytes stuck in the transmitter forever -- particularly if there will be no further transmission until receiving a response.
I can't find any functionality in the drivers that accounts for this possibility. Can you help me find how Linux serial drivers manage this eventuality?
Thanks,
Seth
| |