Dear List,
Using SALSA-Lib 0.0.4, I call:
snd_pcm_open (&playback_handle, argv[1], SND_PCM_STREAM_PLAYBACK, O_NONBLOCK); 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 (playback_handle, hw_params, 16000, 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_set_period_size (playback_handle, hw_params, 1024, 0) 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, 1024) snd_pcm_sw_params_set_start_threshold (playback_handle, sw_params, 4096U) snd_pcm_sw_params (playback_handle, sw_params) snd_pcm_prepare (playback_handle)
int pdcount = snd_pcm_poll_descriptors_count (playback_handle); struct pollfd fds [10]; pdcount = snd_pcm_poll_descriptors (playback_handle, fds, 10);
while ((frames_to_deliver = snd_pcm_avail_update (playback_handle)) > 1024) { snd_pcm_writei (playback_handle, &buf, 1024) }
while (1) { retval = poll (fds, 1, 5000);
frames_to_deliver = snd_pcm_avail_update (playback_handle); fprintf (stderr, "Frames to deliver was: %ld\n", frames_to_deliver);
frames_to_deliver = frames_to_deliver > 4096 ? 4096 : frames_to_deliver; playback_callback (frames_to_deliver); }
The "retval = poll (fds, 1, 5000)" statement does not appear to wait for the playback buffer to be sufficiently emptied. When this same program is run with the standard alsa-lib, the POLL statement will wait until there is room in the buffer to accomodate 1024 additional samples. When run with SALSA-lib, it appears to return immediately and snd_pcm_avail_update indicates that there is only space for about 80 more samples.
The code is being cross-compiled and tested on an ARM processor (PXA270) which is running linux kernel 2.6.21. This same code sequence -does- operate properly (in the same ARM test environment) when compiled against AlsaLib 1.0.13.
Another apparent (and perhaps relevent) difference between AlsaLib and SALSA-Lib is that if I open the PCM stream with O_NONBLOCK and then call snd_pcm_poll_descriptors, AlsaLib gives me a FD = 4, whereas SALSA-Lib reports an FD = 3;
Thanks, Scott.