Once thing I have noticed, is that with the alc650, we used to have VRA (alsa 0.9.8), but the 1.0.2 intel8x0 driver ignores the VRA and fixes itself at 48000.
So, before I never needed the sample rate converters, but as it now fixes the rate at 48000, I need the sample rate converters, and they don't actually work.
I have found out what the problem is with the resamplers not working.
I was using: -
err = snd_pcm_sw_params_set_start_threshold(handle, swparams, buffer_size); <- note buffer_size.
So, the state will stay in SND_PCM_STATE_PREPARED state until the buffer is full.
Inside snd_pcm_write_areas() [in alsa-lib] we have a snd_pcm_wait statement before we write frames into the buffer.
if (((snd_pcm_uframes_t)avail < pcm->avail_min && size > (snd_pcm_uframes_t)avail) || (size >= pcm->xfer_align && (snd_pcm_uframes_t)avail < pcm->xfer_align)) {
then it calls snd_pcm_wait()
So, this will call snd_pcm_wait() until avail >= pcm->avail_min. This will only become true if we are in SND_PCM_STATE_RUNNING state.
below the snd_pcm_wait(), we do try to execute snd_pcm_start() to get us into SND_PCM_STATE_RUNNING, but this only gets executed if: -
if (state == SND_PCM_STATE_PREPARED && hw_avail >= (snd_pcm_sframes_t) pcm->start_threshold) {
So, we will only reach a running state if the buffer is FULL, but the buffer will NEVER become full, because of the previous snd_pcm_wait();
CATCH22!!!
I think a fix to this would be to limit as follows: - start_threshold <= (buffer_size - avail_min)
I have fixed the issue for now, just by setting the "start_threshold" to something other than buffer_size. But I think some work needs to be done with alsa-lib to prevent this deadlock situation ever happening in alsa-lib.
From the application writers point of view, if the buffer is X bytes long, and one used snd_pcm_writei() to write X+10 bytes, the buffer should become full. Currently, that is not always the case, and alsa-lib instead locks in snd_pcm_wait().
I attach a patch that fixes alsa-lib.
All it does it call snd_pcm_start() just before snd_pcm_wait() and due to the if statement just above it, will only happen when the buffer is going to be filled, therefore ensuring that even if "start_threshold" is set too high, snd_pcm_start() will always be called if the buffer is full, or about to become full.
Cheers James
--- src/pcm/pcm.c.old 2004-02-02 23:07:14.355587424 +0000 +++ src/pcm/pcm.c 2004-02-02 23:07:19.871748840 +0000 @@ -6033,6 +6033,11 @@ } else if (((snd_pcm_uframes_t)avail < pcm->avail_min && size > (snd_pcm_uframes_t)avail) || (size >= pcm->xfer_align && (snd_pcm_uframes_t)avail < pcm->xfer_align)) { + if (state == SND_PCM_STATE_PREPARED ) { + err = snd_pcm_start(pcm); + if (err < 0) + goto _end; + } if (pcm->mode & SND_PCM_NONBLOCK) { err = -EAGAIN; goto _end;