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authorPierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>2012-10-22 16:42:15 -0500
committerTakashi Iwai <tiwai@suse.de>2012-10-23 16:13:48 +0200
commit4eeaaeaea1cec60a25979678182720dc91308550 (patch)
treeef6895d3ff86454cc6348e2efde2313eceb24471 /sound/core/pcm_native.c
parent0e8014d772a7639f48d234b23dc4ce97335cce7f (diff)
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>
Diffstat (limited to 'sound/core/pcm_native.c')
-rw-r--r--sound/core/pcm_native.c2
1 files changed, 2 insertions, 0 deletions
diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
index 5e12e5bacbb..7c800012fff 100644
--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -594,6 +594,8 @@ int snd_pcm_status(struct snd_pcm_substream *substream,
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;
}
}