ALSA: core: add hooks for audio timestamps
ALSA did not provide any direct means to infer the audio time for A/V
sync and system/audio time correlations (eg. PulseAudio).
Applications had to track the number of samples read/written and
add/subtract the number of samples queued in the ring buffer. This
accounting led to small errors, typically several samples, due to the
two-step process. Computing the audio time in the kernel is more
direct, as all the information is available in the same routines.
Also add new .audio_wallclock routine to enable fine-grain synchronization
between monotonic system time and audio hardware time.
Using the wallclock, if supported in hardware, allows for a
much better sub-microsecond precision and a common drift tracking for
all devices sharing the same wall clock (master clock).
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
index 5e12e5b..7c80001 100644
--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -594,6 +594,8 @@
snd_pcm_update_hw_ptr(substream);
if (runtime->tstamp_mode == SNDRV_PCM_TSTAMP_ENABLE) {
status->tstamp = runtime->status->tstamp;
+ status->audio_tstamp =
+ runtime->status->audio_tstamp;
goto _tstamp_end;
}
}
