2011/3/20 Ivan Sorokin sorokin@rain.ifmo.ru

Hello!

I use slightly modified test/pcm.c in write_and_poll mode.

My program looks like this:

snd_pcm_open with SND_PCM_NONBLOCK snd_pcm_set_params

infinite loop poll for snd_pcm_poll_descriptors snd_pcm_poll_descriptors_revents if POLLOUT flag is set snd_pcm_writei

Everything works, but snd_pcm_writei sometimes returns -EAGAIN. The probability of when snd_pcm_writei returns -EAGAIN depends on buffer size that I pass to it. ExperimentallyI found out that when I call snd_pcm_writei with 940 bytes buffers (maybe something related to period size?) it never returns -EAGAIN.

Why poll returns when there is no place for new data? Is it ok to ignore EAGAIN and just start another poll? Is there any recommended buffer size for snd_pcm_writei?

My test program: https://github.com/sorokin/asoundpp/blob/master/sine_async.cpp (94 LOC)

Most sound cards does not have 0.5 second buffer , only a few sound card (e.g. snd-hda-intel has 4Mb buffer but snd-intel8x0 only has 64Kb buffer

d.set_params(SND_PCM_FORMAT_S16, SND_PCM_ACCESS_RW_INTERLEAVED, 1, RATE, true, 500000);