[alsa-devel] [PATCH] pcm: support for audio wallclock

[Takashi Iwai]

At Wed, 13 Jun 2012 15:27:47 -0500,
Pierre-Louis Bossart wrote:
> 
> add new snd_pcm_status_get_htstamp_wallclk() routine to
> query the audio timestamps read from the wallclock.
> 
> Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart at linux.intel.com>
> ---
>  include/pcm.h          |    1 +
>  include/sound/asound.h |    7 ++++++-
>  src/pcm/pcm.c          |   16 ++++++++++++++++
>  3 files changed, 23 insertions(+), 1 deletions(-)
> 
> diff --git a/include/pcm.h b/include/pcm.h
> index 4997557..325c0ea 100644
> --- a/include/pcm.h
> +++ b/include/pcm.h
> @@ -858,6 +858,7 @@ void snd_pcm_status_get_trigger_tstamp(const snd_pcm_status_t *obj, snd_timestam
>  void snd_pcm_status_get_trigger_htstamp(const snd_pcm_status_t *obj, snd_htimestamp_t *ptr);
>  void snd_pcm_status_get_tstamp(const snd_pcm_status_t *obj, snd_timestamp_t *ptr);
>  void snd_pcm_status_get_htstamp(const snd_pcm_status_t *obj, snd_htimestamp_t *ptr);
> +void snd_pcm_status_get_htstamp_wallclk(const snd_pcm_status_t *obj, snd_htimestamp_t *ptr);
>  snd_pcm_sframes_t snd_pcm_status_get_delay(const snd_pcm_status_t *obj);
>  snd_pcm_uframes_t snd_pcm_status_get_avail(const snd_pcm_status_t *obj);
>  snd_pcm_uframes_t snd_pcm_status_get_avail_max(const snd_pcm_status_t *obj);
> diff --git a/include/sound/asound.h b/include/sound/asound.h
> index 07c03fa..c186fd6 100644
> --- a/include/sound/asound.h
> +++ b/include/sound/asound.h
> @@ -285,6 +285,7 @@ enum sndrv_pcm_subformat {
>  #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 */
>  
>  enum sndrv_pcm_state {
>  	SNDRV_PCM_STATE_OPEN = 0,	/* stream is open */
> @@ -426,7 +427,10 @@ struct sndrv_pcm_status {
>  	sndrv_pcm_uframes_t avail_max;	/* max frames available on hw since last status */
>  	sndrv_pcm_uframes_t overrange;	/* count of ADC (capture) overrange detections from last status */
>  	int suspended_state;		/* suspended stream state */
> -	unsigned char reserved[60];	/* must be filled with zero */
> +	union {
> +		unsigned char reserved[60];	/* must be filled with zero */
> +		struct timespec audio_tstamp;	/* audio wall clock timestamp */
> +	} ext;
>  };
>  
>  struct sndrv_pcm_mmap_status {
> @@ -434,6 +438,7 @@ struct sndrv_pcm_mmap_status {
>  	int pad1;			/* Needed for 64 bit alignment */
>  	sndrv_pcm_uframes_t hw_ptr;	/* RO: hw ptr (0...boundary-1) */
>  	struct timespec tstamp;		/* Timestamp */
> +	struct timespec audio_tstamp;	/* audio wall clock timestamp */
>  	int suspended_state;		/* RO: suspended stream state */
>  };
>  
> diff --git a/src/pcm/pcm.c b/src/pcm/pcm.c
> index 18b43b3..2221865 100644
> --- a/src/pcm/pcm.c
> +++ b/src/pcm/pcm.c
> @@ -6213,6 +6213,22 @@ void snd_pcm_status_get_htstamp(const snd_pcm_status_t *obj, snd_htimestamp_t *p
>  use_default_symbol_version(__snd_pcm_status_get_htstamp, snd_pcm_status_get_htstamp, ALSA_0.9.0rc8);

You need to provide a function to indicate whether htstamp_wallclk is
available or not.  Since the function returning tstamp_wallclk is a
void function and it itself can't return the error, user can't know
whether it's a bogus value or not.

And that function should check whether the running PCM protocol
version is high enough to support the new ABI.

>  /** 
> + * \brief Get "now" hi-res audio wallclock timestamp from a PCM status container
> + * \param obj pointer to #snd_pcm_status_t
> + * \param ptr Pointer to returned timestamp
> + */
> +#ifndef DOXYGEN
> +void INTERNAL(snd_pcm_status_get_htstamp_wallclk)(const snd_pcm_status_t *obj, snd_htimestamp_t *ptr)
> +#else
> +void snd_pcm_status_get_htstamp_wallclk(const snd_pcm_status_t *obj, snd_htimestamp_t *ptr)
> +#endif

I think you can avoid this hack for the new functions.

> +{
> +	assert(obj && ptr);
> +	*ptr = obj->ext.audio_tstamp;
> +}
> +use_default_symbol_version(__snd_pcm_status_get_htstamp_wallclk, snd_pcm_status_get_htstamp_wallclk, ALSA_0.9.0rc8);  /* FIXME, no idea why this is needed */

Ditto.  It was needed just for those functions that have been added to
0.9.0rc8 release.


Takashi