On Sun, 1 Jul 2012, Frederik Himpe wrote: > > A usbmon trace would be more helpful. Or perhaps a pair of traces, one > > for the USB-2 port and one for the USB-3 port. See the instructions in > > Documentation/usb/usbmon.txt. > > OK, I created a usbmon trace both from the USB-2 port as the USB-3 port. > During the trace, I connected the USB webcam to the USB port and started > mplayer, which failed on USB-2 but worked fine on USB-3. > > The two traces can be found here: > http://artipc10.vub.ac.be/~frederik/webcam/ There are two significant differences between the USB-2 and USB-3 traces, although I don't know what to make of them. Initially it looks like the driver writes a bunch of values to the webcam and asks it to repeat them back. That's what happens in the USB-3 trace, anyway. The USB-2 trace shows the values being written, but when asked to repeat them back the webcam sends nothing. For example, with USB-3: ffff8804085042c0 470397794 S Co:3:003:0 s 22 01 0100 0086 0003 3 = 803e00 ffff8804085042c0 470399896 C Co:3:003:0 0 3 > ffff8804085042c0 470400004 S Ci:3:003:0 s a2 81 0100 0086 0003 3 < ffff8804085042c0 470401270 C Ci:3:003:0 0 3 = 803e00 The 803e00 values get sent and then received. The analogous part of the USB-2 trace shows: ffff88040cc1f5c0 208122798 S Co:1:006:0 s 22 01 0100 0086 0003 3 = 803e00 ffff88040cc1f5c0 208124781 C Co:1:006:0 0 3 > ffff88040cc1f5c0 208124818 S Ci:1:006:0 s a2 81 0100 0086 0003 3 < ffff88040cc1f5c0 208126156 C Ci:1:006:0 0 0 Exactly the same values are sent and the request is the same, but no data gets returned. I have no idea what that means. Secondly, both traces show that the webcam stopped being used for a short time and was suspended. A few seconds later, when it was resumed again, it worked okay in the USB-3 trace. But in the USB-2 trace, it didn't. After the resume it failed to reply to the first packet sent (a Get-Device-Status request), and thus it had to be re-enumerated. Have you tried using the webcam on a different computer? Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
