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touch issues improvement (not complete fix)

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  • touch issues improvement (not complete fix)


    I have a 4DCAPE-70T and I have also experienced the issues with the jitter and erratic behavior of the touchscreen.

    I played a bit with the driver and I found a quick fix to improve a bit this weird behavior.

    Basically, during debugging, the erratic behavior would get reduced because of the print statements.

    So instead, I introduced a small 10 microsecond delay between the reads and it somewhat helped a bit.

    The kernel used for this is the one patched from this repository: git://

    Perhaps this will help others find a better fix.

    The patch:

    diff --git a/drivers/input/touchscreen/ti_am335x_tsc.c b/drivers/input/touchscreen/ti_am335x_tsc.c
    index 8933c91..feaad2b 100644
    --- a/drivers/input/touchscreen/ti_am335x_tsc.c
    +++ b/drivers/input/touchscreen/ti_am335x_tsc.c
    @@ -222,6 +222,7 @@ static void titsc_read_coordinates(struct titsc *ts_dev,
    * if true the value is reported to the sub system.
    for (i = 0; i < fifocount; i++) {
    + udelay(10); // reduces a bit erratic behavior on 4DCAPE-70T
    read = titsc_readl(ts_dev, REG_FIFO0);

    channel = (read & 0xf0000) >> 16;

  • #2

    Hello AlexGal

    Welcome to the forum.

    Yes the touch erratic issue has been known for some time, and is due to the Kernel.
    It has been raised on the forum and a fix is now available, of which we are testing out as we speak.

    4D Systems does not have anything to do with software development for the BBB.

    As per the site, here is a Debian release that has the fix applied. There is an Archlinux patch also available.

    An eMMC "flasher" which can be installed to any 2GB or greater microSD card. [BBB-eMMC-flasher-debian-7.3-2014-01-22-2gb.img.xz]

    It takes about 10-15 Minutes to dd microSD (2GB), 15 minutes to flash eMMC (look for full 4 LED's)

    4GB standalone image that can be flashed to any 4GB or greater. [bone-debian-7.3-2014-01-22-4gb.img.xz]

    It takes about 20-30 Minutes to dd microSD (4GB)

    Hope that helps



    • #3

      Hi James,

      I tried the patch on!topic/beagleboard/SXTaSUf4aSk however it did not do anything for the 4DCAPE-70T.

      Let me know if the latest image works well on yours; I will test it as well just to make sure.




      • #4

        Hi Alex

        Yes I just tried the 4gb Standalone image, held the button down and booted from SD, and the touch is working well.

        Trying Archlinux now.