On Mon, 25 May 2009, Hans de Goede wrote: > Hi All, > > Please keep me in the CC, I'm not subscribed to the list. > > Short intro: I'm a FOSS / Linux developer for 10 years now, > the last year or so I've been working on improving webcam > support under Linux, see: > http://fedoraproject.org/wiki/Features/BetterWebcamSupport > > While working on this I noticed that one of the older > Logitech cams I have for testing with, did not work due to > bandwidth problems. It turns out this one only has 1 > (non-zero isoc speed) altsetting, claiming max usb 1.1 bandwidth > for the isoc endpoint. Since I was also playing audio through > a usb-1.1 audio device at the time, the not working was not > a surprise. Stopping the audio fixes this. > > As a workaround to be able to play both audio and test the > cam I plugged the cam into the usb-2.0 hub built into my > dell monitor, but even with the audio not playing it will > not work when connected this way. Doing isochronous transfers to a USB-1.1 device through a USB-2.0 hub is a weak point in the ehci-hcd driver. (In fact, it's a weak point of the USB-2.0 specification!) You're much better off avoiding it, if you can. The best approach would be to plug both the audio and webcam devices directly into your computer, but on different USB buses so there's contention for bandwidth. As a second-best attempt, you could try plugging the webcam into the computer and the audio device into the monitor's hub. > USB controller: nVidia Corporation MCP55 USB > > lsusb -v output attached. > > I'll happily try any patches, run kernels build with extra > debugging info, etc. To help track this down. 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
