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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>
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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include/uapi/sound/asound.h
+5 -2
View File
@@ -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 {