ALSA: core: add hooks for audio timestamps

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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>

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This commit is contained in:

Pierre-Louis Bossart 2012-10-22 16:42:15 -05:00 • committed by Takashi Iwai

parent 0e8014d772

commit 4eeaaeaea1

5 changed files with 50 additions and 12 deletions

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2

include/sound/pcm.h

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7

include/uapi/sound/asound.h

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19

sound/core/pcm_compat.c

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32

sound/core/pcm_lib.c

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2

sound/core/pcm_native.c

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