On Thu, 21 Feb 2002, Kai Vehmanen wrote:
> On Tue, 19 Feb 2002, Jaroslav Kysela wrote:
>
> >> I'm still a bit puzzled why I didn't get xruns in the test case quoted
> >> below, but until I can reproduce the problem, there's not much to discuss
> > You posted this sw params on alsa-devel a few days ago:
> [....]
> > sw_params:
> > stop_threshold: 4294967295
> [...]
> > As you can see, the stop_threshold is set to UMAX_INT. In case when
> > stop_threshold is above ring buffer size, then it means for drivers: I
> > don't care about xruns, don't report them. The stop threshold must be
> > equal to ring buffer size to get xruns when no more frames are in ring
> > buffer.
>
> Hmm, makes sense. This raises a few new questions:
>
> 1) Is 'avail > stop_threshold' the only condition when a stream
> can move from RUNNING to XRUN state? The only places I located
> in the current source tree, where this state change happens, were
> in alsa-kernel/core/pcm_lib.c, functions
> snd_pcm_update_hw_ptr_interrupt() and snd_pcm_update_hw_ptr().
>
> 2) If (1) is true, why does runnig jack produces xruns every
> now and then...? The stop_threshold is UMAX_INT for
> both directions and it should never occur that over
> buffer_size samples is writable to, or readable from
> the pcm device.
>
> And to save your time ;), here's one possible explanation to (2):
>
> Looking at jackd code, one possibility is that the we are only getting an
> EPIPE from snd_pcm_avail_update(), but the stream is still in RUNNING
> state. At least in alsa-lib/src/pcm/pcm_hw.c:snd_pcm_hw_avail_update()
> we have a test for:
>
> --cut--
> if (avail > pcm->buffer_size)
> return -EPIPE;
> --cut--
>
> This would trigger jackd's xrun handling code, but leave state to RUNNING.
> Am I on the right track here?
Yes, this condition is faulty. It should be 'avail >= pcm->stop_threshold'.
Fixed in CVS and thanks for verbose error detection.
Jaroslav
-----
Jaroslav Kysela <[EMAIL PROTECTED]>
Linux Kernel Sound Maintainer
ALSA Project http://www.alsa-project.org
SuSE Linux http://www.suse.com
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