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

[Tanu Kaskinen]

On Mon, 2013-12-09 at 13:23 +0800, Raymond Yau wrote:
> 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 ?

I don't know.

-- 
Tanu