Re: [alsa-devel] Fw: BUG: Kernel panic when disconnecting Edirol USB2 audio interface

[Lee Revell <rlrevell@joe-job.com>]

On Mon, 2005-06-27 at 20:31 -0700, david-b@pacbell.net wrote:
> > From: Lee Revell <rlrevell@joe-job.com>
> > Date: Mon, 27 Jun 2005 22:30:11 -0400
> >
> > On Mon, 2005-06-27 at 19:03 -0700, david-b@pacbell.net wrote:
> > > > With kernel 2.6.12 + "[PATCH] ehci-hcd - fix page pointer allocation in 
> > > > itd_patch()"), using jackd in realtime mode at 44.1kHz with 64 
> > > > frames/period and 4 periods/buffer, I get a stream of xruns of about 
> > > > 0.020 ms, several per second.
> > > 
> > > In USB, one frame == 1 msec.  Most EHCI silicon using the 2.6.12 code
> > > will get unhappy with 256 msec per ISO URB, so I hope you're using
> > > "frame" without a necessary adjective ... ;)
> > > 
> >
> > "frame" = audio frame (4 bytes with S16LE).
> > "USB frame" = 1 msec
> 
> No.  "frame" == ambiguous.  This message is on a USB list, where the
> no-adjective version means "USB frame".  It's also cross-posted to
> a list where the no-adjective version means something very different.
> 
> The only solution that removes ambiguity for _everyone_ is to ensure
> that such words never appear without an adjective.
> 

OK, makes sense.

So what the poster was saying was that if he uses 64 audio frames per
period, which at 44.1KHz requires the audio interface to deliver a chink
of data every ~1.4ms, he gets periodic xruns, IOW the audio interface is
not able to do that.  If he uses 128, he gets no xruns, so he's getting
a chunk of data every 2.8ms, but it's corrupted, hence the crackling.

Lee



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