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SubjectRe: 2.6.11, USB: High latency?
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On Wed, 2005-03-30 at 14:57 -0800, David Brownell wrote:
> Quoth rlevell@joe-job.com:
> > I think this is connected to a problem people have been reporting on the
> > Linux audio lists. With some USB chipsets, USB audio interfaces just
> > don't work. There are dropouts even at very high latencies.
>
> Well, I'd not yet expect USB audio to work over EHCI quite yet,
> though one of the patches Greg just posted should help some of
> the issues with full speed iso through USB 2.0 hubs. (At least
> for OUT transfers as to speakers.)
>

This is the exact configuration of one of the users who reported the
problem on LAU. Got a pointer to the patch? And what's the issue with
IN transfers?

> You might consider reporting such issues on the Linux-USB list.
> It's been ages since anyone reported such a bug with the OHCI
> or UHCI drivers ... probably why folk have assumed there are
> no problems there.
>

OK, good to know.

>
> Something to consider specifically with audio. That uses the
> isochronous transfer mode, reserving USB bandwidth. But I've
> certainly seen systems with PCI busses that are severely clogged,
> so that the USB controllers have a hard time accessing main
> memory. Even a perfectly functional USB stack will have a hard
> time with such hardware!

Unlikely because it works under Windows. We're not all that far behind
however; USB audio on that OS did not really work until XP SP1. Also,
if that were a widespread problem we would be seeing problems with PCI
devices too.

Also please fix the threading in your email client.

Lee

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