[alsa-devel] SALSA-Lib: Playback overrun on initial PCM start

[Takashi Iwai]

At Fri, 29 Jun 2007 11:24:09 -0400,
J. Scott Merritt wrote:
> 
> On Fri, 29 Jun 2007 11:25:16 +0200
> Takashi Iwai <tiwai at suse.de> wrote:
> 
> > At Thu, 28 Jun 2007 15:01:08 -0400,
> > J. Scott Merritt wrote:
> > > 
> > > Dear List,
> > > 
> > > Using SALSA-Lib 0.0.3, I call:	
> > > 
> > > snd_pcm_open (&playback_handle, argv[1], SND_PCM_STREAM_PLAYBACK, 0);
> > > snd_pcm_hw_params_malloc (&hw_params);
> > > snd_pcm_hw_params_any (playback_handle, hw_params);
> > > snd_pcm_hw_params_set_access (playback_handle, hw_params, SND_PCM_ACCESS_RW_INTERLEAVED);
> > > snd_pcm_hw_params_set_format (playback_handle, hw_params, SND_PCM_FORMAT_S16_LE));
> > > snd_pcm_hw_params_set_rate_near (playback_handle, hw_params, 44100, 0);
> > > snd_pcm_hw_params_set_channels (playback_handle, hw_params, 2);
> > > snd_pcm_hw_params_set_buffer_size_last (playback_handle, hw_params, &bfrsize);
> > > snd_pcm_hw_params_get_buffer_size (hw_params, &bfrsize);
> > > snd_pcm_hw_params (playback_handle, hw_params);
> > > snd_pcm_hw_params_free (hw_params);
> > > 	
> > > snd_pcm_sw_params_malloc (&sw_params);
> > > snd_pcm_sw_params_current (playback_handle, sw_params);
> > > snd_pcm_sw_params_set_avail_min (playback_handle, sw_params, 4096);
> > > snd_pcm_sw_params_set_start_threshold (playback_handle, sw_params, 10000U);
> > > snd_pcm_sw_params_set_xfer_align (playback_handle, sw_params, 1);
> > > snd_pcm_sw_params (playback_handle, sw_params);
> > > 	
> > > state = snd_pcm_state (playback_handle);
> > > frames_to_deliver = snd_pcm_avail_update (playback_handle);
> > > 
> > > while ((frames_to_deliver = snd_pcm_avail_update (playback_handle)) > 4096) {
> > >    snd_pcm_writei (playback_handle, &buf, 4096) }
> > > 
> > > 
> > > As soon as the buffer start threshold is reached, or alternatively
> > > if I manually start PCM stream, the PCM stream reports an overrun
> > > (i.e. "Broken Pipe").  If I then examine the PCM state, it is in the
> > > overrun (XRUN) state.
> > 
> > What are the buffer and period sizes?  Did you try alsa-lib with hw,
> > too, right?
> 
> In sample program above, buffer size is set to "last", which results
> in a buffer size of 32768 (which matches the allocation in the kernel driver).
> The sample programs above does not establish a period size and is unknown.
> 
> I added code to set the period size to 1024 frames and experienced the
> same (overrun) result.   I also forced the buffer size to 8192 and lowered
> the sample rate to 16 kHz and did not see any improvement.
> 
> Yes, the same exact code runs properly on the target hardware with
> alsa-lib 1.0.13.

OK, looks like a bug in salsa-lib, then.
I fixed some remaining bugs and release 0.0.4 now.  Please give it a
try.  (Note that it might take some time until the ftp server is
exported / mirrored.)


thanks,

Takashi