[alsa-devel] [PATCH v5 04/10] ALSA: usb: update trigger timestamp on first non-zero URB submitted

[Takashi Iwai]

At Fri,  6 Feb 2015 15:55:53 -0600,
Pierre-Louis Bossart wrote:
> 
> The first URBs are submitted during the prepare stage. When .trigger is
> called, the ALSA core saves a trigger tstamp that doesn't correspond to
> the actual time when the samples are submitted. The trigger_tstamp is
> now updated when the first data are submitted to avoid any time offsets.
> 
> A usb-specific trigger_tstamp_pending_update flag is used for now,
> at some point the flag would need to move to the ALSA core, USB
> is not the only interface where silent block transfers are programmed
> as part of the prepare stage, with actual data enabled when .trigger
> is called.
> 
> Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart at linux.intel.com>

Applied, thanks.


Takashi


> ---
>  sound/usb/card.h | 2 ++
>  sound/usb/pcm.c  | 9 +++++++++
>  2 files changed, 11 insertions(+)
> 
> diff --git a/sound/usb/card.h b/sound/usb/card.h
> index 97acb90..ef580b4 100644
> --- a/sound/usb/card.h
> +++ b/sound/usb/card.h
> @@ -153,6 +153,8 @@ struct snd_usb_substream {
>  		int channel;
>  		int byte_idx;
>  	} dsd_dop;
> +
> +	bool trigger_tstamp_pending_update; /* trigger timestamp being updated from initial estimate */
>  };
>  
>  struct snd_usb_stream {
> diff --git a/sound/usb/pcm.c b/sound/usb/pcm.c
> index 0d8aba5..b4ef410 100644
> --- a/sound/usb/pcm.c
> +++ b/sound/usb/pcm.c
> @@ -1464,6 +1464,14 @@ static void prepare_playback_urb(struct snd_usb_substream *subs,
>  	subs->last_frame_number = usb_get_current_frame_number(subs->dev);
>  	subs->last_frame_number &= 0xFF; /* keep 8 LSBs */
>  
> +	if (subs->trigger_tstamp_pending_update) {
> +		/* this is the first actual URB submitted,
> +		 * update trigger timestamp to reflect actual start time
> +		 */
> +		snd_pcm_gettime(runtime, &runtime->trigger_tstamp);
> +		subs->trigger_tstamp_pending_update = false;
> +	}
> +
>  	spin_unlock_irqrestore(&subs->lock, flags);
>  	urb->transfer_buffer_length = bytes;
>  	if (period_elapsed)
> @@ -1550,6 +1558,7 @@ static int snd_usb_substream_playback_trigger(struct snd_pcm_substream *substrea
>  
>  	switch (cmd) {
>  	case SNDRV_PCM_TRIGGER_START:
> +		subs->trigger_tstamp_pending_update = true;
>  	case SNDRV_PCM_TRIGGER_PAUSE_RELEASE:
>  		subs->data_endpoint->prepare_data_urb = prepare_playback_urb;
>  		subs->data_endpoint->retire_data_urb = retire_playback_urb;
> -- 
> 1.9.1
> 
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