snd_pcm_playback_data(9) centos man page | unix.com

SND_PCM_PLAYBACK_DAT(9) 					   Sound Devices					   SND_PCM_PLAYBACK_DAT(9)

NAME
       snd_pcm_playback_data - check whether any data exists on the playback buffer

SYNOPSIS
       int snd_pcm_playback_data(struct snd_pcm_substream * substream);

ARGUMENTS
       substream
	   the pcm substream instance

DESCRIPTION
       Checks whether any data exists on the playback buffer.

RETURN
       Non-zero if any data exists, or zero if not. If stop_threshold is bigger or equal to boundary, then this function returns always non-zero.

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Kernel Hackers Manual 3.10					     June 2014						   SND_PCM_PLAYBACK_DAT(9)