[alsa-devel] [PATCH v2 2/3] ALSA: core: add hooks for audio timestamps
Takashi Iwai
tiwai at suse.de
Tue Oct 9 11:33:17 CEST 2012
At Mon, 8 Oct 2012 12:11:57 -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 at linux.intel.com>
> ---
> include/sound/asound.h | 7 +++++--
> include/sound/pcm.h | 2 ++
> sound/core/pcm_compat.c | 13 +++++++++++--
> sound/core/pcm_lib.c | 32 ++++++++++++++++++++++++++++++--
> sound/core/pcm_native.c | 2 ++
> 5 files changed, 50 insertions(+), 6 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,
> + 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);
> diff --git a/sound/core/pcm_compat.c b/sound/core/pcm_compat.c
> index 91cdf94..ab4c953 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 timespec audio_tstamp;
It must be struct compat_timespec...
> + unsigned char reserved[60-sizeof(struct timespec)];
> } __attribute__((packed));
>
>
> @@ -215,7 +216,9 @@ static int snd_pcm_status_user_compat(struct snd_pcm_substream *substream,
> 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) ||
> + put_user(status.audio_tstamp.tv_sec, &src->audio_tstamp.tv_sec) ||
> + put_user(status.audio_tstamp.tv_nsec, &src->audio_tstamp.tv_nsec))
... and use compat_put_timespec().
> return -EFAULT;
>
> return err;
> @@ -364,6 +367,7 @@ struct snd_pcm_mmap_status32 {
> u32 hw_ptr;
> struct compat_timespec tstamp;
> s32 suspended_state;
> + struct compat_timespec audio_tstamp;
Ditto.
> } __attribute__((packed));
>
> struct snd_pcm_mmap_control32 {
> @@ -426,12 +430,17 @@ 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) ||
> put_user(sstatus.suspended_state, &src->s.status.suspended_state) ||
> + put_user(sstatus.audio_tstamp.tv_sec,
> + &src->s.status.audio_tstamp.tv_sec) ||
> + put_user(sstatus.audio_tstamp.tv_nsec,
> + &src->s.status.audio_tstamp.tv_nsec) ||
Ditto.
Takashi
> put_user(scontrol.appl_ptr, &src->c.control.appl_ptr) ||
> put_user(scontrol.avail_min, &src->c.control.avail_min))
> return -EFAULT;
> diff --git a/sound/core/pcm_lib.c b/sound/core/pcm_lib.c
> index ec996ca..2bccd16 100644
> --- a/sound/core/pcm_lib.c
> +++ b/sound/core/pcm_lib.c
> @@ -315,6 +315,7 @@ 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;
> @@ -327,9 +328,14 @@ 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,
> BUG_ON(crossed_boundary < 0);
> 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);
> }
>
> diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
> index 53b5ada..c5206f4 100644
> --- a/sound/core/pcm_native.c
> +++ b/sound/core/pcm_native.c
> @@ -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;
> }
> }
> --
> 1.7.9.5
>
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