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_lib.c b/sound/core/pcm_lib.c
index 3dc029e..c4840ff 100644
--- a/sound/core/pcm_lib.c
+++ b/sound/core/pcm_lib.c
@@ -316,6 +316,7 @@
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 @@
*/
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 @@
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);
}