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

[Takashi Iwai]

At Fri, 29 Jun 2007 12:26:45 -0400,
J. Scott Merritt wrote:
> 
> On Fri, 29 Jun 2007 18:07:20 +0200
> Takashi Iwai <tiwai at suse.de> wrote:
> 
> > 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.)
> 
> Much better :)
> 
> I no longer get the PlayBack overrun on PCM start.  However, it appears
> that "poll" or the snd_pcm_sw_params_set_avail_min (=4096) is not being
> properly honored.  With the normal alsa-lib, when the "poll" returns
> snd_pcm_avail_update reports that space is available for 4096 frames.
> However, in my initial testing, when running with SALSA lib, only about
> 100 frames or so are available when the poll returns.
> 
> I will examine this more closely.

Found out another bug.  Try the patch below.

Thanks for reporting!


Takashi

diff -r ad2c81608e10 src/pcm.c
--- a/src/pcm.c	Fri Jun 29 17:59:52 2007 +0200
+++ b/src/pcm.c	Fri Jun 29 19:12:04 2007 +0200
@@ -857,6 +857,7 @@ static int snd_pcm_hw_mmap_status(snd_pc
 		pcm->mmap_status = NULL;
 		goto no_mmap;
 	}
+	pcm->mmap_control->avail_min = 1;
 	return 0;
 
  no_mmap:
@@ -865,6 +866,7 @@ static int snd_pcm_hw_mmap_status(snd_pc
 		return -ENOMEM;
 	pcm->mmap_status = &pcm->sync_ptr->s.status;
 	pcm->mmap_control = &pcm->sync_ptr->c.control;
+	pcm->mmap_control->avail_min = 1;
 	_snd_pcm_sync_ptr(pcm, 0);
 	return 0;
 }
diff -r ad2c81608e10 src/pcm_params.c
--- a/src/pcm_params.c	Fri Jun 29 17:59:52 2007 +0200
+++ b/src/pcm_params.c	Fri Jun 29 19:12:04 2007 +0200
@@ -1052,6 +1052,7 @@ int snd_pcm_sw_params(snd_pcm_t *pcm, sn
 	if (ioctl(pcm->fd, SNDRV_PCM_IOCTL_SW_PARAMS, params) < 0)
 		return -errno;
 	pcm->sw_params = *params;
+	pcm->mmap_control->avail_min = params->avail_min;
 	return 0;
 }