[alsa-devel] [PATCH RFC 2/9] ALSA: core: allow for trigger_tstamp snapshot in .trigger

[Takashi Iwai]

At Mon,  8 Dec 2014 16:23:39 -0600,
Pierre-Louis Bossart wrote:
> 
> Don't use generic snapshot of trigger_tstamp if low-level driver or
> hardware can get a more precise value for better audio/system time
> synchronization.
> 
> Also add definitions for delayed updates if actual trigger tstamp
> can be only be provided after a delay due to hardware constraints.
> 
> Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart at linux.intel.com>
> ---
>  include/sound/pcm.h     | 2 ++
>  sound/core/pcm_native.c | 6 +++++-
>  2 files changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/include/sound/pcm.h b/include/sound/pcm.h
> index 1e7f74a..83c669f 100644
> --- a/include/sound/pcm.h
> +++ b/include/sound/pcm.h
> @@ -281,6 +281,8 @@ struct snd_pcm_runtime {
>  	/* -- Status -- */
>  	struct snd_pcm_substream *trigger_master;
>  	struct timespec trigger_tstamp;	/* trigger timestamp */
> +	int trigger_tstamp_latched;     /* trigger timestamp latched in low-level driver/hardware */

Better to use bool nowadays.

> +	int trigger_tstamp_pending_update; /* trigger timestamp being updated from initial estimate */

This isn't used at all in this patch.  I found it being used in the
later usb-audio patch.  If it's the only place, can't it be rather put
locally to usb-audio object instead of the common pcm runtime?

>  	int overrange;
>  	snd_pcm_uframes_t avail_max;
>  	snd_pcm_uframes_t hw_ptr_base;	/* Position at buffer restart */
> diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
> index 5dc83fb..37a7137 100644
> --- a/sound/core/pcm_native.c
> +++ b/sound/core/pcm_native.c
> @@ -806,10 +806,14 @@ static int snd_pcm_channel_info_user(struct snd_pcm_substream *substream,
>  static void snd_pcm_trigger_tstamp(struct snd_pcm_substream *substream)
>  {
>  	struct snd_pcm_runtime *runtime = substream->runtime;
> +
>  	if (runtime->trigger_master == NULL)
>  		return;
>  	if (runtime->trigger_master == substream) {
> -		snd_pcm_gettime(runtime, &runtime->trigger_tstamp);
> +		if (runtime->trigger_tstamp_latched == 0)
> +			snd_pcm_gettime(runtime, &runtime->trigger_tstamp);
> +		else
> +			runtime->trigger_tstamp_latched = 0;

IMO, it's better to clear the flat at the beginning of PCM trigger
commonly.  Looking at the later patch, you clear in each driver's
callback.  This should be moved into the common place.


thanks,

Takashi