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Thread: USB error codes

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  1. #1

    USB error codes

    I'm attempting to design a USB device, so I'm testing it stage-by-stage on my Linux box. When I run usbmon and plug the device in, I get output like this (among many other lines I've omitted):

    ecfaf400 3.327041 S Co:2:001:0 s 23 01 0014 0003 0000 0
    ecfaf400 3.327049 C Co:2:001:0 0 0
    ecfaf400 3.428025 S Ci:2:000:0 s 80 06 0100 0000 0040 64 <
    ecfaf400 3.548291 C Ci:2:000:0 -84 0
    And the corresponding dmesg entry looks like this:
    usb 2-3: new low speed USB device using ohci_hcd and address 80
    usb 2-3: device descriptor read/64, error -84
    The USB host is indicating this "error -84". Does anyone know if that is a Linux-specific USB error code? And if so, is there a reference table that describes the trigger for each error code (i.e., what does error 84 mean)?


  2. #2
    Managed to answer my own question. This particular error is programmed in from the kernel source code file errno.h. It corresponds to EILSEQ, aka illegal sequence. For my USB device, I'm guessing this means I'm sending a badly formatted device descriptor.

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