[LAD] interrupt-drive ALSA returning buffers too small

I was going through Paul Davis's excellent tutorial on the ALSA API: http://www.equalarea.com/paul/alsa-audio.html#interruptex I've set alsa to wake me up every N frames. However, when I awake, I find that I often have fewer than N frames available: int err; uint32_t N = 2048, frames_to_deliver; assert( 0 == ((N-1)&N) ); /* power of 2 */ /*...*/ snd_pcm_sw_params_set_avail_min (playback_handle, sw_params, N) /* ... */ while(1) { err = snd_pcm_wait(playback_handle, 1000); assert(err >= 0); /* OK */ frames_to_deliver = snd_pcm_avail_update(playback_handle); assert(frames_to_deliver >= 0); /* OK */ /* this fails about every other cycle: */ assert(frames_to_deliver >= N); } E.g. with N = 2048, I'll typically get a stream that looks like 1996, 2048, 2048, 1990, 2048, 1999, 2048... Any ideas? -gabriel