[pulseaudio-discuss] [PATCH] alsa: Disable timer-scheduling for PCMs with the BATCH flag

[Raymond Yau]

2013/12/6 Tanu Kaskinen <tanu.kaskinen at linux.intel.com>

> On Sat, 2013-11-30 at 18:07 +0100, Lars-Peter Clausen wrote:
> > PCM Devices which have the BATCH flag set update the PCM pointer only
> with
> > period size granularity. Using timer based scheduling does not have any
> > advantage in this mode. For one devices which have that flag set usually
> update
> > the position pointer in software after getting the period interrupt. So
> > disabling the period interrupt is not possible for this kind of devices.
> > Furthermore writing to or reading from the buffer slice for the current
> period
> > is not possible since the position inside the buffer is not known. On
> the other
> > hand the tsched algorithm seems to get easily confused for this kind of
> > hardware, which results in garbled audio output. This typically means
> that timer
> > based scheduling needs to be manually disabled on systems with such
> devices.
> > Auto disabling tsched in this case allows these systems to run with the
> default
> > configuration.
> >
> > Signed-off-by: Lars-Peter Clausen <lars at metafoo.de>
> > ---
> >  src/modules/alsa/alsa-util.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> >
> > diff --git a/src/modules/alsa/alsa-util.c b/src/modules/alsa/alsa-util.c
> > index 75f5858..4b24e47 100644
> > --- a/src/modules/alsa/alsa-util.c
> > +++ b/src/modules/alsa/alsa-util.c
> > @@ -245,6 +245,10 @@ int pa_alsa_set_hw_params(
> >      if (!pa_alsa_pcm_is_hw(pcm_handle))
> >          _use_tsched = false;
> >
> > +    /* The PCM pointer is only updated with period granularity */
> > +    if (snd_pcm_hw_params_is_batch(hwparams))
> > +        _use_tsched = false;
> > +
> >  #if (SND_LIB_VERSION >= ((1<<16)|(0<<8)|24)) /* API additions in 1.0.24
> */
> >      if (_use_tsched) {
> >
>
> Thanks! I applied the patch.
>
> --
>

Are you patch sufficient ?

In alsa-lib , snd_pcm_sw_params_set_avail_min always return zero

int snd_pcm_sw_params_set_avail_min(snd_pcm_t *pcm, snd_pcm_sw_params_t
*params, snd_pcm_uframes_t val)
{
         assert(pcm && params);
         /* Fix avail_min if it's below period size.  The period_size
          * defines the minimal wake-up timing accuracy, so it doesn't
          * make sense to set below that.
          */
         if (val < pcm->period_size)
                 val = pcm->period_size;
         params->avail_min = val;
         return 0;
}


http://cgit.freedesktop.org/pulseaudio/pulseaudio/commit/src/modules/alsa/alsa-sink.c?id=26a270a934f0f174f7bd7eb89e85301963721deb

/* We need at last one frame in the used part of the buffer */
- avail_min = (snd_pcm_uframes_t) u->hwbuf_unused_frames + 1;
+ avail_min = (snd_pcm_uframes_t) u->hwbuf_unused / u->frame_size + 1;

do pulseaudio need to keep at least one periods instead of more than 1
frames for those driver which update hwptr in periods ?
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