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| author | Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com> | 2012-10-22 16:42:15 -0500 |
|---|---|---|
| committer | Takashi Iwai <tiwai@suse.de> | 2012-10-23 16:13:48 +0200 |
| commit | 4eeaaeaea1cec60a25979678182720dc91308550 (patch) | |
| tree | ef6895d3ff86454cc6348e2efde2313eceb24471 /include/sound | |
| parent | 0e8014d772a7639f48d234b23dc4ce97335cce7f (diff) | |
| download | lwn-4eeaaeaea1cec60a25979678182720dc91308550.tar.gz lwn-4eeaaeaea1cec60a25979678182720dc91308550.zip | |
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 'include/sound')
| -rw-r--r-- | include/sound/pcm.h | 2 |
1 files changed, 2 insertions, 0 deletions
diff --git a/include/sound/pcm.h b/include/sound/pcm.h index 28fd9f95f9ba..45c1981c9ca2 100644 --- a/include/sound/pcm.h +++ b/include/sound/pcm.h @@ -71,6 +71,8 @@ struct snd_pcm_ops { int (*prepare)(struct snd_pcm_substream *substream); int (*trigger)(struct snd_pcm_substream *substream, int cmd); snd_pcm_uframes_t (*pointer)(struct snd_pcm_substream *substream); + int (*wall_clock)(struct snd_pcm_substream *substream, + struct timespec *audio_ts); int (*copy)(struct snd_pcm_substream *substream, int channel, snd_pcm_uframes_t pos, void __user *buf, snd_pcm_uframes_t count); |