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.
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?
This could be a usb timing issue on the usb side tickled by a sensitive
device, a bad assumption on alsa's part, or a bad dongle design. Thoughts?
Thanks again for the help.
David
On Sat, Feb 07, 2009 at 04:46:57PM -0500, Alan Stern wrote:
> On Sat, 7 Feb 2009, David wrote:
>
> > Greetings everyone.
> >
> > I have a peculiar problem with USB MIDI timing that appears beginning with
> > kernel 2.6.24, and still persists in 2.6.28.4. Kernel 2.6.23.17 works fine.
> >
> > The symptom is some note events seem to arrive noticeably late. The problem
> > is most apparent with rapid scales or situations where multiple note events
> > are supposed to be played at once (chords).
> >
> > The MIDI interface dongle I am using is only a full speed device.
> >
> > The problem is _not_ present when connected directly to the root hub (the
> > MIDI dongle binds to the OHCI driver), and it is not present with
> > ehci_hcd unloaded or unbind'ed from the EHCI interface handling the bus
> > (forcing everything to use ohci), even when using external hubs.
> >
> > The problem _is_ present when the MIDI dongle is connected to any
> > external USB 2.0 hub and EHCI is in use. I have reproduced on 2 different
> > hosts with two different EHCI chipsets (NVIDIA and ICH9) and about 4
> > different hubs. No EHCI setup with kernel >=2.6.24 works right. Not
> > knowing anything else, I would suspect the problem has something to do with
> > scheduling at the hub's TT.
>
> For problems like this, git -bisect may be the best approach.
>
> Alan Stern
>
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