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Commit 4eeaaeae authored by Pierre-Louis Bossart's avatar Pierre-Louis Bossart Committed by Takashi Iwai
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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: default avatarPierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: default avatarTakashi Iwai <tiwai@suse.de>
parent 0e8014d7

include/sound/pcm.h

+2 −0
Original line number Diff line number Diff line
@@ -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);

include/uapi/sound/asound.h

+5 −2
Original line number Diff line number Diff line
@@ -136,7 +136,7 @@ struct snd_hwdep_dsp_image { 
 *                                                                           *

 *****************************************************************************/



#define SNDRV_PCM_VERSION		SNDRV_PROTOCOL_VERSION(2, 0, 10)

#define SNDRV_PCM_VERSION		SNDRV_PROTOCOL_VERSION(2, 0, 11)



typedef unsigned long snd_pcm_uframes_t;

typedef signed long snd_pcm_sframes_t;
@@ -258,6 +258,7 @@ typedef int __bitwise snd_pcm_subformat_t; 
#define SNDRV_PCM_INFO_JOINT_DUPLEX	0x00200000	/* playback and capture stream are somewhat correlated */

#define SNDRV_PCM_INFO_SYNC_START	0x00400000	/* pcm support some kind of sync go */

#define SNDRV_PCM_INFO_NO_PERIOD_WAKEUP	0x00800000	/* period wakeup can be disabled */

#define SNDRV_PCM_INFO_HAS_WALL_CLOCK   0x01000000      /* has audio wall clock for audio/system time sync */

#define SNDRV_PCM_INFO_FIFO_IN_FRAMES	0x80000000	/* internal kernel flag - FIFO size is in frames */



typedef int __bitwise snd_pcm_state_t;
@@ -406,7 +407,8 @@ struct snd_pcm_status { 
	snd_pcm_uframes_t avail_max;	/* max frames available on hw since last status */

	snd_pcm_uframes_t overrange;	/* count of ADC (capture) overrange detections from last status */

	snd_pcm_state_t suspended_state; /* suspended stream state */

	unsigned char reserved[60];	/* must be filled with zero */

	struct timespec audio_tstamp;	/* from sample counter or wall clock */

	unsigned char reserved[60-sizeof(struct timespec)]; /* must be filled with zero */

};



struct snd_pcm_mmap_status {
@@ -415,6 +417,7 @@ struct snd_pcm_mmap_status { 
	snd_pcm_uframes_t hw_ptr;	/* RO: hw ptr (0...boundary-1) */

	struct timespec tstamp;		/* Timestamp */

	snd_pcm_state_t suspended_state; /* RO: suspended stream state */

	struct timespec audio_tstamp;	/* from sample counter or wall clock */

};



struct snd_pcm_mmap_control {

sound/core/pcm_compat.c

+11 −8
Original line number Diff line number Diff line
@@ -190,7 +190,8 @@ struct snd_pcm_status32 { 
	u32 avail_max;

	u32 overrange;

	s32 suspended_state;

	unsigned char reserved[60];

	struct compat_timespec audio_tstamp;

	unsigned char reserved[60-sizeof(struct compat_timespec)];

} __attribute__((packed));
@@ -205,17 +206,16 @@ static int snd_pcm_status_user_compat(struct snd_pcm_substream *substream, 
		return err;



	if (put_user(status.state, &src->state) ||

	    put_user(status.trigger_tstamp.tv_sec, &src->trigger_tstamp.tv_sec) ||

	    put_user(status.trigger_tstamp.tv_nsec, &src->trigger_tstamp.tv_nsec) ||

	    put_user(status.tstamp.tv_sec, &src->tstamp.tv_sec) ||

	    put_user(status.tstamp.tv_nsec, &src->tstamp.tv_nsec) ||

	    compat_put_timespec(&status.trigger_tstamp, &src->trigger_tstamp) ||

	    compat_put_timespec(&status.tstamp, &src->tstamp) ||

	    put_user(status.appl_ptr, &src->appl_ptr) ||

	    put_user(status.hw_ptr, &src->hw_ptr) ||

	    put_user(status.delay, &src->delay) ||

	    put_user(status.avail, &src->avail) ||

	    put_user(status.avail_max, &src->avail_max) ||

	    put_user(status.overrange, &src->overrange) ||

	    put_user(status.suspended_state, &src->suspended_state))

	    put_user(status.suspended_state, &src->suspended_state) ||

	    compat_put_timespec(&status.audio_tstamp, &src->audio_tstamp))

		return -EFAULT;



	return err;
@@ -364,6 +364,7 @@ struct snd_pcm_mmap_status32 { 
	u32 hw_ptr;

	struct compat_timespec tstamp;

	s32 suspended_state;

	struct compat_timespec audio_tstamp;

} __attribute__((packed));



struct snd_pcm_mmap_control32 {
@@ -426,12 +427,14 @@ static int snd_pcm_ioctl_sync_ptr_compat(struct snd_pcm_substream *substream, 
	sstatus.hw_ptr = status->hw_ptr % boundary;

	sstatus.tstamp = status->tstamp;

	sstatus.suspended_state = status->suspended_state;

	sstatus.audio_tstamp = status->audio_tstamp;

	snd_pcm_stream_unlock_irq(substream);

	if (put_user(sstatus.state, &src->s.status.state) ||

	    put_user(sstatus.hw_ptr, &src->s.status.hw_ptr) ||

	    put_user(sstatus.tstamp.tv_sec, &src->s.status.tstamp.tv_sec) ||

	    put_user(sstatus.tstamp.tv_nsec, &src->s.status.tstamp.tv_nsec) ||

	    compat_put_timespec(&sstatus.tstamp, &src->s.status.tstamp) ||

	    put_user(sstatus.suspended_state, &src->s.status.suspended_state) ||

	    compat_put_timespec(&sstatus.audio_tstamp,

		    &src->s.status.audio_tstamp) ||

	    put_user(scontrol.appl_ptr, &src->c.control.appl_ptr) ||

	    put_user(scontrol.avail_min, &src->c.control.avail_min))

		return -EFAULT;

sound/core/pcm_lib.c

+30 −2
Original line number Diff line number Diff line
@@ -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);

}

sound/core/pcm_native.c

+2 −0
Original line number Diff line number Diff line
@@ -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;

		}

	}