[pulseaudio-discuss] snd_pcm_avail no reliable

[Arun Raghavan]

On 09-Jun-2015 11:26 am, "Raymond Yau" <superquad.vortex2 at gmail.com> wrote:
>
> >>
> >>
> >>  >
> >>  >   below is what the terminate shows when running pcm_avail.c
> >>  >
> >>  >   uid=0 gid=1007 at nutshell:/ # alsactl_test
> >>  > min_period_size: 8 frames, dir: 0
> >>  > Playback hwparams: FIFO size is 8
> >>  > Hardware PCM card 0 'rsnd-dai.0-dirana3.0' device 0 subdevice 0
> >>  > Its setup is:
> >>  >   stream       : PLAYBACK
> >>  >   access       : RW_INTERLEAVED
> >>  >   format       : S16_LE
> >>  >   subformat    : STD
> >>  >   channels     : 2
> >>  >   rate         : 48000
> >>  >   exact rate   : 48000 (48000/1)
> >>  >   msbits       : 16
> >>  >   buffer_size  : 4096
> >>  >   period_size  : 1024
> >>  >   period_time  : 21333
> >>  >   tstamp_mode  : NONE
> >>  >   period_step  : 1
> >>  >   avail_min    : 1024
> >>  >   period_event : 0
> >>  >   start_threshold  : 1024
> >>  >   stop_threshold   : 4096
> >>  >   silence_threshold: 0
> >>  >   silence_size : 0
> >>  >   boundary     : 1073741824
> >>  >   appl_ptr     : 0
> >>  >   hw_ptr       : 0
> >>  > Playing silence
> >>  > Available: 0, loop iteration: 0
> >>  > Available: 1024, loop iteration: 1469
> >>  > Available: 2048, loop iteration: 5609
> >>  > Available: 3072, loop iteration: 9667
> >>  >
> >>  >  All I got is just the 4 lines.
> >>
> >> If your sound card only increment hw_ptr only at interrupt occur, you
> >> need to increase default_rewind_safeguard from 256 bytes to your
> >> selected period size
> >
> >
> > No. PulseAudio, in timer-scheduling mode, does not use periods at all.
You need to change the driver so that it reports SNDRV_PCM_INFO_BATCH, so
that PulseAudio does not try to use this mode.
> >
> >
> >>
> >> This mean that  your sound card won't work with timer scheduling or
> >> dynamic latency, you can only archieve low latency by decrease period
size
> >> Why do pulseaudio enable timer scheduling when most sound card use IRQ
?
> >
> >
> > Because most broken sound cards driver authors forget to report
SNDRV_PCM_INFO_BATCH?
>
> Why pulseaudio rely on the flag if your program can find out the
granulatity ?

AFAIK, there isn't a way to figure out granularity. Having this would be
nice as we could be more intelligent about our tsched behaviour.

-- Arun
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