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Windows Embedded 8.1 Randomly Does Not Recognize USB Devices RRS feed

  • Question

  • Problem description:  An appliance we are developing running Windows Embedded 8.1 Industry does not recognize any USB devices plugged into CERTAIN ports after being rebooted or turned on.  This only happens intermittently, not after every boot.  When it does happen, only two things make those ports work again:  a reboot, or disabling the Windows Embedded USB Filter and then clicking "Scan for new hardware" in Device Manager.  Also, it is not always the same two USB ports that don't work.  Sometimes the two left ports don't work, and sometimes the two right ports don't work.  

    Each time it happens, one of the internal "Generic USB Hub"s that should be listed in Device Manager is actually not listed.  I know that the Location Path of the hub that is not listed corresponds to the internal hub those non-working ports connect to.  The hub only reappears in Device Manager when I disable the USB filter, then click Scan for New Hardware (or reboot).  Simply disabling the USB filter does not fix the issue, and the USB filter must be disabled before "Scan for New Hardware" will work.

    Hypothesis:  One guess I have is that Windows is booting so quickly that it doesn't allow itself time to detect / enumerate all USB devices before the USB filter turns on.  Also, since I know that the filter has the right permissions (it explicitly calls out permissions for those internal hubs), I don't understand why having the filter enabled prevents the "Scan for new hardware" function from working.

    Possible fix:  Delay the startup of the USB Filter (which is not a process, I believe it is actually a driver), which I don't know how to do, then install devcon.exe and write a batch file to run "devcon rescan" (which I think is the same as doing "Scan for new hardware") before the USB Filter starts up.  

    My team and I would greatly appreciate anyone who can either offer a how-to for my possible fix above (specifically how to delay the start of the USB Filter), or offer any other possible fixes.
    Thursday, July 28, 2016 3:46 AM

All replies

  • If you don't use the USB filter, everything works okay?

    Sean Liming - Book Author: Starter Guide SIM (WEI), Pro Guide to WE8S & WES 7, Pro Guide to POS for .NET - www.annabooks.com / www.seanliming.com

    Thursday, July 28, 2016 1:57 PM
    Moderator
  • Although I don't recall the problem ever happening with the USB filter off, I can't be certain if it did or not.  Since the problem only manifests after about every 20 to 50 boot ups, we haven't yet tested that specifically; however, I am leaning towards doing that in an effort to narrow things down.
    Thursday, July 28, 2016 5:44 PM
  • We just ran the same appliance through 225 boot-then-shutdown cycles using the settings below (in order), without changing anything else, and strangely, the problem didn't occur again once.

    1. 50 cycles with USB Filter OFF, UWF OFF.

    2. 75 cycles with USB Filter ON, UWF OFF.

    3. 50 cycles with USB Filter OFF, UWF ON.

    4. 50 cycles with USB Filter ON, UWF ON.

    One theory I have as to why the problem didn't happen during these tests is that after enabling the USB filter, Windows may need to be rebooted before enabling the write filter, as opposed to simply enabling both filters during the same session.  I believe this because after enabling the USB Filter for the first time on the appliance, I don't recall ever rebooting it either with the write filter totally off or with the filter in a state of activation pending the next boot (until we ran test 1 above).  Also, I remember the problem happening once immediately after enabling both filters for the first time and rebooting.

    I will test my theory on another, identical appliance with a fresh image that initially has all filters disabled.


    Friday, July 29, 2016 10:48 PM