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AM335x USB Babble with 3G USB modem

Baptiste
Prodigy 40 points
Other Parts Discussed in Thread: AM3352

Hi,

I have designed a board based on a AM3352 and i'm facing some random babble interrupt with USB devices.

Here is what i can see on 'dmesg':
  CAUTION: musb: Babble Interrupt Occurred

I'm using Kernel 3.12 from EVM 7.0
I tried some patches like the one that reset the USB after a babble detection, it helps recovering but it's not a solution for 3G communication (the communication aborts frequently)

I've tried the latest USB source code from TI Git (Kernel 3.12.46), the Babble stil occurs but the reset patch has been removed so the situation is worst.

I've heard that it could be an interference issue, how can we solve it by modifying our PCB ?

Thanks in advance
Regards


PS: i've read on the forums that it could also be a power management issue, i can't uncheck anymore powermanagement features due to dependancies, can you confirm this is OK ?

  • 0
    TI__Guru**** 167581 points

    You could add 'usbcore.autosuspend=-1' to uboot bootargs to disable usb power management.

  • 0 in reply to Bin Liu
    Prodigy 40 points

    Thanks a lot for your answer Bin,

    i've tried a

    echo -1 >/sys/module/usbcore/parameters/autosuspend

    which should change the parameter at runtime.

    Unfortunately it doesn't prevent the babble to occur.

    In my situation it doesn't seems to be a power management issue since it happens when the USB devices are working (Establishing GSM connection for the 3G modem for example)

     

  • 0 in reply to Baptiste
    TI__Guru**** 167581 points

    Baptiste said:

    echo -1 >/sys/module/usbcore/parameters/autosuspend

    which should change the parameter at runtime.

    Yes. Ensure you plug the modem after the command.

    Baptiste said:
    In my situation it doesn't seems to be a power management issue since it happens when the USB devices are working (Establishing GSM connection for the 3G modem for example)

    Agreed this is likely not PM related.

    This seems like an electrical issue, giving that USB babble is not uncommon in RF applications. Hope hw experts will leave any comment.