Comment 151 for bug 1201528

[alsa-sink-ALC889 Analog] alsa-sink.c: Underrun!

this seem not alsa driver, it occur whe client did not supply audio and server has nothing to write

in theory, the server have to call snd_pcm_foreward to recover

http://cgit.freedesktop.org/pulseaudio/pulseaudio/log/src/modules/alsa/alsa-sink.c?qt=grep&q=underrun