On Mon, 2 Oct 2006, Laurent Pinchart wrote: > > > > > 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. > > > > > > I'm using an EHCI controller. Does it matter if the USB 1.1 controller is > > > an OHCI or UHCI ? > > > > Is the Logitech webcam a full-speed device or does it use high-speed? If > > it is full-speed, is it behind a high-speed hub? These things will affect > > which controller gets used. If it is behind a high-speed hub, does it > > work better when you connect it directly to the computer? > > The webcam is a high-speed device connected to the root hub.
I see. In that case the companion full-speed controller won't make any difference, since it's not being used. > > For most purposes it doesn't matter whether a full-speed controller is > > OHCI or UHCI. OHCI does more of the work in hardware, so it puts less > > load on the host computer. By the same token, its scheduling is less > > flexible since the host has less direct control. > > > > > It would be nice if you could send me the patch. > > > > See below. Note that it won't have any effect since you're not using a UHCI controller for the webcam. > > How did you determine the source of the problem? Did the engineers at > > Logitech figure it out for you? If so, have they made a similar analysis > > of what happens with Windows to see why it works better? > > They are working on it, but they don't have lots of traces yet. I'll ask them > to send more information on this mailing list directly, this should be > easier. The problem is definitely in the webcam hardware (they are working on > a firmware workaround), but the weird part is it is not triggered by Windows. Very curious. In principle it's possible to change ehci-hcd so that the SETUP transaction of a control transfer is sent in a different microframe from the following IN/OUT transactions. In practice it might be a painfully difficult change to write. 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
