[alsa-devel] [PATCH v4 04/10] ALSA: usb: update trigger timestamp on first non-zero URB submitted

[Takashi Iwai]

At Fri, 30 Jan 2015 17:55:57 -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.
> 
> Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart at linux.intel.com>
> ---
>  sound/usb/pcm.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/sound/usb/pcm.c b/sound/usb/pcm.c
> index 0d8aba5..7c36fc1 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 (runtime->trigger_tstamp_pending_update == 1) {

Ah I see that trigger_tstamp_pending_update is used here at first.
But then I wonder whether this is specific to USB-audio, if there is
no relevant code in PCM core side?  If so, we don't need to add the
field to snd_pcm_runtime but to snb_usb_usbstream instead.

(BTW, for boolean, avoid use of 0 and 1.)


thanks,

Takashi


> +		/* this is the first actual URB submitted,
> +		 * update trigger timestamp to reflect actual start time
> +		 */
> +		snd_pcm_gettime(runtime, &runtime->trigger_tstamp);
> +		runtime->trigger_tstamp_pending_update = 0;
> +	}
> +
>  	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:
> +		substream->runtime->trigger_tstamp_pending_update = 1;
>  	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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