Re: [Alsa-user] buffer size and period size relationship?

[Raymond T. <rt...@go...>]

On Thu, Aug 25, 2011 at 12:15 AM, Clemens Ladisch
<cla...@go...>wrote:

> Raymond Toy wrote:
> > I'm working on an application where I wanted to do double-buffering and
> > tried to set the buffer size to 4096 and the period size to 2048.
>  However,
> > the actual period size used by ALSA is 1365.  In fact, it seems that
> > whatever I choose for the buffer size, the period size used by ALSA is
> 1/3
> > of the buffer size.  Is this a limitation of the audio HW that I'm using?
>
> This is possible.  There isn't any particular combination of buffer/
> period parameters that is guaranteed to be supported with all hardware.
>
> If you want to have two periods, call snd_pcm_hw_params_set_periods
> before try to set the other parameters, but this might fail.
>

I think I tried that and it failed, but I will try again to be sure.


> > cat /proc/asound/cards says:
> >
> >  0 [Intel          ]: HDA-Intel - HDA Intel
> >                       HDA Intel at 0xf8000000 irq 21
>
> HDA is quite flexible, but it's possible that you're using plugins that
> introduce additional restrictions.  What device name are you using in
> your program?  What plugins are shown when you run
> "aplay -D devicename -v something.wav"?
>
>
It says:

 Playing WAVE 'M1F1-int16WE-AFsp.wav' : Signed 16 bit Little Endian, Rate
8000 Hz, Stereo
ALSA <-> PulseAudio PCM I/O Plugin
Its setup is:
  stream       : PLAYBACK
  access       : RW_INTERLEAVED
  format       : S16_LE
  subformat    : STD
  channels     : 2
  rate         : 8000
  exact rate   : 8000 (8000/1)
  msbits       : 16
  buffer_size  : 4000
  period_size  : 1000
  period_time  : 125000
  tstamp_mode  : NONE
  period_step  : 1
  avail_min    : 1000
  period_event : 0
  start_threshold  : 4000
  stop_threshold   : 4000
  silence_threshold: 0
  silence_size : 0
  boundary     : 9007199254740992000

I have read about PulseAudio potentially being a problem, but getting rid of
it is not so easy.  Besides, for the application I'm looking at, I won't
have control over that.

Thanks,

Ray