On Mon, 11 Dec 2006, Ilyes Gouta wrote: > Hi! > > I'm writing a v4l2 USB driver for my webcam, based on ALi's M5603C, > and I have three questions: > > 1) During my experimentations, I discovered that Linux was unable to > handle isochronous URBs where each one contains 256 ISOC packets. I > made a small experiment where I tried to allocate such an URB > (allocation and submit): my box just hang. Can somebody confirm this > behavior?
I have never heard any reports of problems with URBs containing lots of ISO packets. Can you provide more details (kernel version, which host controller driver, perhaps a code extract from your driver)? > 2) Is it possible that one constructor would lock its USB device such > as it only responds to one kind of URBs? Let's say for example, an URB > which has N isochronous packets, each one pointing on M bytes? Is this > possible? No, it isn't possible. The device doesn't know anything about URBs; all it knows is the packets it receives. If N packets arrive, the device cannot tell whether there was a single URB with N packets, or N URBs each with one packet, or anything in between. For IN transfers, the computer doesn't even tell the device how many bytes should be transferred. The device simply sends whatever it wants. > 3) My webcam is supposed to return the ISOC URBs, I submitted using > usb_submit_urb, filled with data. However nothing happens (I don't > received any data): I get my URBs acknowledged back in the completion > handler where I'm resubmitting them again. Any ideas? My webcam has > two endpoints, a control and an isochronous. Do you know about some > webcam models where the OS has to explicitly ACK for ISOC transfers by > submitting URBs to the control endpoint? Did you change the altsetting? According to the USB spec, devices are not supposed to support ISO transfers in an interface's default altsetting. I don't know how webcams work specifically. ISO transfers never have to be acknowledged, but it's certainly possible that they won't get started until you send an appropriate command to the camera. Alan Stern P.S.: Your Subject: line is rather misleading. You're more concerned about webcams than about ALi hardware. ------------------------------------------------------------------------- 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
