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Linux/PROCESSOR-SDK-AM335X: UART software flow control

Benoit TANI
Prodigy 50 points
Part Number: PROCESSOR-SDK-AM335X

Tool/software: Linux

Hi,

I would like to have a status on UART Software flow-control in ti-processor-sdk-linux-rt.

I checked version 05.00.00.15 and 4.03.00.05 and found this comment in "omap_8250_set_termios":

* OMAP rx s/w flow control is borked; the transmitter remains
* stuck off even if rx flow control is subsequently disabled

Is this related to this thread as previous version did not had this comment: e2e.ti.com/.../432849

I would really like to know what is working/not working, and eventually what is planned for this ?

Any help would be greatly appreciated.

Thanks and regards

  • 0
    TI__Guru**** 170625 points

    Hi Benoit,

    From what I was able to find, UART driver support only hardware flow control:

    downloads.ti.com/.../Foundational_Components_Kernel_Drivers.html

    http://processors.wiki.ti.com/index.php/Linux_Core_UART_User's_Guide

    https://e2e.ti.com/support/embedded/linux/f/354/t/576752

    Regards,
    Pavel

  • 0
    TI__Genius 13567 points
    Benoit,
    The official errata document does not mention this UART behavior. And on my bench I confirmed that the UART responds to XON and XOFF special characters. So software flow control is definitely working.

    Tested using kernel v4.14 from the processor SDK 5.0 on an AM437x starterkit EVM and on an OMAP5 evm. I used putty to connect to the serial console and sent the XOFF character using "CTRL+S". After that I can continue typing in putty but nothing is received back from the processor. After sending the XON character using "CTRL+Q" this tells the processor that everything I typed can finally be sent back to me.

    If this does not answer your question please share the details of this particular use case (baud rate, total bytes, etc) and what behavior you are seeing versus the behavior you are expecting.

    Regards,
    Ahmad
  • 0 in reply to Ahmad_Rashed
    Prodigy 50 points

    Hi Ahmad,
    Thank you for you help.

    I can confirm that input sw flow control is ok when testing with a custom board.

    I investigate output XON/XOFF.


    Regards.

    EDIT:

    It seems that the START/STOP should be sent in 'uart_throttle' in 'serial_core.c' except in the case where "UPSTAT_AUTOXOFF" flag is set.

    When "UPSTAT_AUTOXOFF" is set, it should up to the omap_8250_(un)throttle to do the job, which is not the case.