On Sat, 7 Feb 2009, David wrote: > Thanks for the pointers Alan. I'm not a developer and never tinkered with > git before -- pretty slick. > > I've isolated it to a patch made on the alsa side under commit: > > commit a6a712aeb17ff30206ae1bc827d50497d884602a > Author: Clemens Ladisch <clemens@xxxxxxxxxx> > Date: Tue Aug 21 08:56:08 2007 +0200 > > [ALSA] usb-audio: allow output interrupt transfers for MIDI > > Allow output interrupt transfers for some MIDI devices that require > them. > > Signed-off-by: Clemens Ladisch <clemens@xxxxxxxxxx> > Signed-off-by: Jaroslav Kysela <perex@xxxxxxx> > > > The patch effectively changed how alsa interfaces with my midi dongle, going > from using the bulk endpoint to the interrupt one for output. bulk seems to > work, interrupt, not so much when on ehci. That doesn't seem to agree with the description of the patch. Since your device worked okay using only bulk, no one can claim that it _requires_ output interrupt transfers. Hence the patch should not have affected the way the device operates. > I'll go ping the alsa folks that surely know more about the midi interfacing > side of this. But, I have this question for the USB folks: > > Why would interrupt transfers behave differently when using ehci and a hub's > TT vice being native to the ohci hcd? I have no idea. In theory the two ought to be equivalent. (However it should be mentioned that scheduling non-high-speed period transfers is by far the most complicated part of EHCI, and it's quite possible that ehci-hcd still has some bugs in that area.) A USB bus analyzer might be able to detect the differences. The only thing I can think of is that the latency for setting up new transfers might vary. This wouldn't matter if the endpoint's queue is kept full, but maybe the driver allows it to become empty from time to time. 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
