Subject: Re: 2.6.11, USB: High latency?
From: Lee Revell <rlrevell@joe-job.com>
To: David Brownell <david-b@pacbell.net>
Cc: kus Kusche Klaus <kus@keba.com>, stern@rowland.harvard.edu,
       linux-usb-users@lists.sourceforge.net, linux-kernel@vger.kernel.org
In-Reply-To: <200503301457.35464.david-b@pacbell.net>
References: <200503301457.35464.david-b@pacbell.net>
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Date: Wed, 30 Mar 2005 19:51:05 -0500
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[cc list restored]

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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