diff options
| 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 /sound/core/pcm_lib.c | |
| parent | 0e8014d772a7639f48d234b23dc4ce97335cce7f (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_lib.c')
| -rw-r--r-- | sound/core/pcm_lib.c | 32 |
1 files changed, 30 insertions, 2 deletions
diff --git a/sound/core/pcm_lib.c b/sound/core/pcm_lib.c index 3dc029e106a2..c4840ff75d00 100644 --- a/sound/core/pcm_lib.c +++ b/sound/core/pcm_lib.c @@ -316,6 +316,7 @@ static int snd_pcm_update_hw_ptr0(struct snd_pcm_substream *substream, unsigned long jdelta; unsigned long curr_jiffies; struct timespec curr_tstamp; + struct timespec audio_tstamp; int crossed_boundary = 0; old_hw_ptr = runtime->status->hw_ptr; @@ -328,9 +329,14 @@ static int snd_pcm_update_hw_ptr0(struct snd_pcm_substream *substream, */ pos = substream->ops->pointer(substream); curr_jiffies = jiffies; - if (runtime->tstamp_mode == SNDRV_PCM_TSTAMP_ENABLE) + if (runtime->tstamp_mode == SNDRV_PCM_TSTAMP_ENABLE) { snd_pcm_gettime(runtime, (struct timespec *)&curr_tstamp); + if ((runtime->hw.info & SNDRV_PCM_INFO_HAS_WALL_CLOCK) && + (substream->ops->wall_clock)) + substream->ops->wall_clock(substream, &audio_tstamp); + } + if (pos == SNDRV_PCM_POS_XRUN) { xrun(substream); return -EPIPE; @@ -520,9 +526,31 @@ static int snd_pcm_update_hw_ptr0(struct snd_pcm_substream *substream, snd_BUG_ON(crossed_boundary != 1); runtime->hw_ptr_wrap += runtime->boundary; } - if (runtime->tstamp_mode == SNDRV_PCM_TSTAMP_ENABLE) + if (runtime->tstamp_mode == SNDRV_PCM_TSTAMP_ENABLE) { runtime->status->tstamp = curr_tstamp; + if (!(runtime->hw.info & SNDRV_PCM_INFO_HAS_WALL_CLOCK)) { + /* + * no wall clock available, provide audio timestamp + * derived from pointer position+delay + */ + u64 audio_frames, audio_nsecs; + + if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK) + audio_frames = runtime->hw_ptr_wrap + + runtime->status->hw_ptr + - runtime->delay; + else + audio_frames = runtime->hw_ptr_wrap + + runtime->status->hw_ptr + + runtime->delay; + audio_nsecs = div_u64(audio_frames * 1000000000LL, + runtime->rate); + audio_tstamp = ns_to_timespec(audio_nsecs); + } + runtime->status->audio_tstamp = audio_tstamp; + } + return snd_pcm_update_state(substream, runtime); } |