Re: OSS sound emulation broken between 2.6.0-test2 and test3

[Jaroslav Kysela]

On Sat, 27 Dec 2003, Martin J. Bligh wrote:

> >> > Something appears to have broken OSS sound emulation between 
> >> > test2 and test3. Best I can tell (despite the appearance of the BK logs), 
> >> > that included ALSA updates 0.9.5 and 0.9.6. Hopefully someone who
> >> > understands the sound architecture better than I can fix this?
> >> > 
> >> 
> >> I wont say I understand it, but a quick look seems the major change is
> >> the addition of the 'whole-frag' and 'no-silence' opts.  You might try
> >> the following to revert what 'no-silence' change at least does:
> >> 
> >> --
> >>  # echo 'xmms 0 0 no-silence' > /proc/asound/card0/pcm0p/oss
> >>  # echo 'xmms 0 0 whole-frag' > /proc/asound/card0/pcm0p/oss
> >> --
> > 
> > Thanks, that fixes it for me. I too have been seeing terrible problems
> > with XMMS since the early 2.6 pre- kernels.
> > 
> > Because it only happens in XMMS I thought it was one of those
> > application bugs brought out by scheduler changes. I now use Zinf BTW
> > -It's better for large music collections (although not as stable or
> > flash).
> > 
> > I guess someone ought to revert the standard behaviour.
> 
> OK, the following patch from Andrew fixes it up 80% or so, but I still 
> don't think it's as good as test2 was - turning on whole-frag seems to
> fix the rest of it. It's much more difficult to tell now though, so I'd 
> like other people's opinions on it. If you want to switch between the
> two, the above switches it on, and:
> 
> # echo 'clear' > /proc/asound/card0/pcm0p/oss
> 
> switches whole-frag back off. I'm using a 192kbps MP3 to test it, repeating
> the first 30s of the same song again and again (I'm gonna hate that song 
> soon ;-)). Different bitrates might give better differentation of the problem.
> 
> Please, please experiment with this, and let us know.
> 
> M.
> 
> --- compile/sound/core/oss/pcm_oss.c.old	Mon Nov 17 18:29:43 2003
> +++ compile/sound/core/oss/pcm_oss.c	Sat Dec 27 10:32:30 2003
> @@ -814,7 +814,7 @@
>  			xfer += tmp;
>  			if (substream->oss.setup == NULL || !substream->oss.setup->wholefrag ||
>  			    runtime->oss.buffer_used == runtime->oss.period_bytes) {
> -				tmp = snd_pcm_oss_write2(substream, runtime->oss.buffer, runtime->oss.buffer_used, 1);
> +				tmp = snd_pcm_oss_write2(substream, runtime->oss.buffer, runtime->oss.period_bytes, 1);
>  				if (tmp <= 0)
>  					return xfer > 0 ? (snd_pcm_sframes_t)xfer : tmp;
>  				runtime->oss.bytes += tmp;

It's not a good fix. The problem might be that the rate convert plugin is 
activated. When small chunks are passed to this plugin, the quality drops.
You can check it with this command (and compare native and OSS rates):

  cat /proc/asound/card0/pcm0p/sub0/*

Also, we fixed some OSS emulation errors in our latest code which is 
available here:

  bk pull http://linux-sound.bkbits.net/linux-sound

or

  ftp://ftp.alsa-project.org/pub/kernel-patches/alsa-bk-2003-12-05.patch.gz

I will prepare new patch for recent kernel soon.

						Jaroslav

-----
Jaroslav Kysela <perex@xxxxxxx>
Linux Kernel Sound Maintainer
ALSA Project, SuSE Labs
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