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USB not connecting after Reset

Barry Andrews
Genius 3460 points
Other Parts Discussed in Thread: TM4C129ENCPDT

I am using TM4C129ENCPDT processor to act as USB Host to CDC USB device.

An older board of mine populated just over 12 months ago works fine,

However new batch of processors work correctly after power up but when you do a hardware reset they don't detect the USB device anymore.

Power the board down and up again and they detect the USB device correctly.

After either a hardware reset or watchdog reset and they don't detect USB device again until I once again power the board down.

I have tried two different boards from our latest batch and they both exhibit this symptom.

Go back to my older board and it works fine every time.

Is there an issue with the USB hardware on these newer batch of processors? or a change to USB initialisation?

I have checked the Erata spmz850f.pdf and there are 5 USB issues listed but none of them seem related to this.

I am using tirtos_tivac_2_16_01_14

  • 0
    Genius 3460 points
    Just one further bit of information.
    Both working board and non working boards have revision code G4 on the processor.

    Working CPU has
    YF
    TM4C129
    ENCPDTI2
    45ADoHW

    Suspect board CPU has
    YF
    TM4C129
    ENCPDTI3
    56A3VGw
  • 0 in reply to Barry Andrews
    Genius 3460 points
    Turned out to be a USB modem assembly error.
    It was missing a resistor on the reset pin and as such it wasn't resetting and thought the USB line was still active.
    Is there anyway that I could have told it to disconnect through the USB stack?
  • 0
    TI__Guru**** 244400 points
    Hello Barry,

    Was the USB modem a standard out of box or something that was assembled?

    Regards
    Amit
  • 0 in reply to Amit Ashara
    Genius 3460 points
    Hello Amit

    It was custom PCB which had options to match Sierra Wireless pin outs vs UBlox pin outs.
    For some reason Sierra Wireless used non standard pin for rest on their MC8775V and onwards devices.
    They put an analog voltage out onto pin 22 of the mini pci express so you cannot use the normal rest pin with these devices.
    They then used pin 33 as their reset pin.

    The modem board had a resistor option to select pin 22 or pin 33 for the reset.
    It was incorrectly populated with pin 33.
    The wireless disable pin 20 disables the 3G side but didn't reset the USB side for the UBlox modem (Resets both for other modem manufacturers).

    So when I thought I was resetting the modem I was just shutting down the 3G side and the USB was maintained.
    This meant when the USB stack started there was no USB connect message and hence no enumeration.

    Regards
    Barry
  • 0 in reply to Barry Andrews
    TI__Guru**** 244400 points
    Hello Barry,

    Thanks for the explanation.

    "An older board of mine populated just over 12 months ago works fine, However new batch of processors work correctly after power up but when you do a hardware reset they don't detect the USB device anymore."

    So was there a change of schematics or just that wrong resistor was populated due to an misinterpreted assembly instruction?

    Regards
    Amit
  • 0 in reply to Amit Ashara
    Genius 3460 points
    Hello Amit

    I was an error on the build list for the batch (wrong option selected).
    My older board had the reset populated for both positions so was actually resetting the modem correctly (But wouldn't have worked with Sierra Wireless).

    Was a lucky catch before batch of 500 devices went out with the issue.

    Regards
    Barry