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OMAP35x UART speed change

Kris Kelley
Prodigy 30 points


All, I am trying to change the speed of a serial UART on a gumstix WaterSTORM to 3,686,400 and the standard Linux drivers only support 460,800. The OMAP35x Applications Processor Technical Reference Manual (spruf98y.pdf) says that the speed can be set that high via "software" however does not tell me how or if a driver is needed to do so. Any help would be much appreciated. Thank you.

  • 0
    TI__Guru 65405 points

    Hi Kris,

    There are various ways to change the UART baud rate settings. You can change the register settings which are describe in the OMAP35x TRM Table 17-30. UART Baud Rate Settings where you can choose DLH_REG and DLL_REG values for desired speed. Then follow the sequence described in the OMAP35x TRM section 17.5.1 UART Programming Model.
    An other way is to change the UART baud rate in the source code by the following c code:

    #include <stropts.h>
#include <asm/termios.h>

struct termios2 tio;
ioctl(fd, TCGETS2, &tio);
tio.c_cflag &= ~CBAUD;
tio.c_cflag |= BOTHER;
tio.c_ispeed = 3686400;
tio.c_ospeed = 3686400;
ioctl(fd, TCSETS2, &tio);



    You can find more ways to change the UART baud rate at:
    stackoverflow.com/.../how-to-set-baud-rate-to-307200-on-linux

    BR
    Tsvetolin Shulev

  • 0 in reply to Cvetolin Shulev-XID
    Prodigy 30 points

    hello tsvetolin,

    Seems like the source code you provided doesn't work.

    #include <stropts.h>
    #include <asm/termios.h>

    struct termios2 tio;
    ioctl(fd, TCGETS2, &tio);
    tio.c_cflag &= ~CBAUD;
    tio.c_cflag |= BOTHER;
    tio.c_ispeed = 3686400;
    tio.c_ospeed = 3686400;
    ioctl(fd, TCSETS2, &tio);

    When I do this and check the baud rate afterwards by "stty -F /dev/ttyS0" it shows the baud rate as 9600. or a Step I am missing?

    Is it possible that there is some sort of resister that needs to be pulled up on the board to allow high speed data transmission?

  • 0 in reply to Kris Kelley
    TI__Guru 65405 points
    Kris,

    I suppose that the above source code is not working because the UART baud rate of 3686400 bps is non-standard for Linux. Therefore I suggest you to change register values according to OMAP35x TRM description.

    BR
    Tsvetolin Shulev