At Fri, 12 Oct 2012 12:05:36 -0500, Pierre-Louis Bossart wrote:
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
include/sound/asound.h | 7 +++++-- include/sound/pcm.h | 2 ++ sound/core/pcm_compat.c | 19 +++++++++++-------- sound/core/pcm_lib.c | 32 ++++++++++++++++++++++++++++++-- sound/core/pcm_native.c | 2 ++ 5 files changed, 50 insertions(+), 12 deletions(-)
diff --git a/include/sound/asound.h b/include/sound/asound.h index 0876a1e..2d1ba63 100644 --- a/include/sound/asound.h +++ b/include/sound/asound.h @@ -152,7 +152,7 @@ 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; @@ -274,6 +274,7 @@ 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; @@ -422,7 +423,8 @@ 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 { @@ -431,6 +433,7 @@ 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 { diff --git a/include/sound/pcm.h b/include/sound/pcm.h index ba13e0b..e2f1d48 100644 --- a/include/sound/pcm.h +++ b/include/sound/pcm.h @@ -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,
int (*copy)(struct snd_pcm_substream *substream, int channel, snd_pcm_uframes_t pos, void __user *buf, snd_pcm_uframes_t count);struct timespec *audio_ts);
diff --git a/sound/core/pcm_compat.c b/sound/core/pcm_compat.c index 91cdf94..3648ae3 100644 --- a/sound/core/pcm_compat.c +++ b/sound/core/pcm_compat.c @@ -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 timespec)];
This must be sizeof(struct compat_timespec).
Takashi