On Tue, Jul 27, 2010 at 12:23 AM, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > On Mon, 26 Jul 2010, Sam Gentle wrote: >> On Mon, Jul 26, 2010 at 2:14 AM, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: >> > On Sun, 25 Jul 2010, Sam Gentle wrote: >> >> When I attempt to record from it, I get "ALSA start: broken pipe" and >> >> this error in my dmesg: "cannot submit datapipe for urb 0, error -28: >> >> not enough bandwidth" >> > >> > Can you provide a usbmon trace? >> >> While I was doing this I made a discovery - arecord actually works (I >> was doing testing using xwax). It looks like the problem might have >> something to do with opening the device in duplex mode, but that's all >> I've got. > > The traces show that, as you discovered, the problem occurs only when > the device is used for both input and output at the same time. Even > more than that, it occurs only when the output is started first (which > is what happened with the xwax and jackd-duplex tests). When the input > is started first (as in the arecord-aplay test), it works okay. Aha! I tried a few more contrived aplay/arecord tests and it's exactly as you say. > Ultimately this comes down to weaknesses in ehci-hcd's scheduling of > periodic transfers through Transaction Translators. That whole part of > the driver needs to be rewritten. > > For now, your best bet may be to force the built-in hub to connect at > full speed instead of high speed. You can do this by writing the hub's > port number to the "companion" file in the EHCI controller's sysfs > directory. For example, in your "connect" log the hub was attached to > port 6 on bus 1, so you could do: > > echo 6 >/sys/bus/usb/devices/usb1/../companion Hm. There are no files named companion anywhere in my /sys/bus/usb tree. A post here from a year and a half ago suggests I might need to disable CONFIG_USB_EHCI_ROOT_HUB_TT - is that it? Sam -- 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
