On Wed, 27 Sep 2006, Laurent Pinchart wrote: > Hi everybody, > > I'm developing a Linux driver for a Logitech USB webcam. A few users reported > that the webcam stopped responding under some conditions. After some > investigation, I found out that the device either timed-out or returned a > STALL handshake during a control transfer on endpoint 0. > > Logitech has been kind enough to investigate the problem. It seems a hardware > bug is triggered when the control transfer transactions are sent "too fast". > Preliminary results show that the hardware misses the second transaction in a > control transfer when both the SETUP and IN/OUT transactions are in the same > USB frame. > > I was wondering if anyone has ever seen such behaviour with other devices.
I have, or something very similar. IIRC it was some sort of USB wireless keyboard/mouse controller built into a laptop. It wouldn't enumerate if the transactions came too close together, although after it was configured there didn't seem to be any problem. > It > seems the bug is never triggered when using Microsoft Windows, so I suspect > that Linux uses a faster scheduler. Is there a way to hack the USB scheduler > to make it split control transfers across USB frames ? We would like to test > if the hardware bug would then be still triggered. Which host controller driver are you using? uhci-hcd always splits control transfers like this (each transaction in a different frame) for unconfigured devices. If you want to hack uhci-hcd so that it splits up control transfers all the time, I can send you a patch. As far as I know, it's impossible to make OHCI hardware do the same thing. BTW, Windows does not split up control transfers for devices after they are configured. Not in general, anyway -- the Logitech device might be an exception. Alan Stern ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys -- and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV _______________________________________________ linux-usb-devel@lists.sourceforge.net To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
