On Fri, 30 Sep 2016 14:43:30 +0200,
Subhransu S. Prusty wrote:
>
> From: Pierre-Louis Bossart <pierre-louis.bossart@xxxxxxxxxxxxxxx>
>
> For playback usages, the endpoints are started before the prepare
> step, and valid audio data will be rendered with a delay that
> cannot be recovered.
> Worst-case the initial delay due to buffering of empty URBS can
> be up to 12ms
>
> Tested with audio_time:
>
> Timestamps without delay taken into account:
> test$ ./audio_time -Dhw:1,0 -p
> playback: systime: 120093327 nsec, audio time 125000000 nsec, systime delta -4906673
> playback: systime: 245090755 nsec, audio time 250000000 nsec, systime delta -4909245
> playback: systime: 370034641 nsec, audio time 375000000 nsec, systime delta -4965359
> playback: systime: 495089634 nsec, audio time 500000000 nsec, systime delta -4910366
>
> Timestamps with delay taken into account (12ms delay shown)
> test$ ./audio_time -Dhw:1,0 -p -d
> playback: systime: 120095090 nsec, audio time 108000000 nsec, systime delta 12095090
> playback: systime: 245090932 nsec, audio time 232000000 nsec, systime delta 13090932
> playback: systime: 370091792 nsec, audio time 357000000 nsec, systime delta 13091792
> playback: systime: 495092309 nsec, audio time 482000000 nsec, systime delta 13092309
This is really a fix unlike other patches in the series.
Please split it from others, so that we can apply it easily.
Takashi
>
> Suggested-by: Rakesh Ughreja <rakesh.ughreja@xxxxxxxxx>
> Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@xxxxxxxxxxxxxxx>
> Signed-off-by: Subhransu S. Prusty <subhransu.s.prusty@xxxxxxxxx>
> ---
> sound/usb/card.h | 1 +
> sound/usb/pcm.c | 32 +++++++++++++++++++++++++++++---
> 2 files changed, 30 insertions(+), 3 deletions(-)
>
> diff --git a/sound/usb/card.h b/sound/usb/card.h
> index 71778ca..d128058 100644
> --- a/sound/usb/card.h
> +++ b/sound/usb/card.h
> @@ -148,6 +148,7 @@ struct snd_usb_substream {
>
> int last_frame_number; /* stored frame number */
> int last_delay; /* stored delay */
> + int start_delay; /* initial delay due to empty frames */
>
> struct {
> int marker;
> diff --git a/sound/usb/pcm.c b/sound/usb/pcm.c
> index 5bcc729..2bf7537 100644
> --- a/sound/usb/pcm.c
> +++ b/sound/usb/pcm.c
> @@ -86,6 +86,7 @@ static snd_pcm_uframes_t snd_usb_pcm_pointer(struct snd_pcm_substream *substream
> hwptr_done = subs->hwptr_done;
> substream->runtime->delay = snd_usb_pcm_delay(subs,
> substream->runtime->rate);
> + substream->runtime->delay += subs->start_delay;
> spin_unlock(&subs->lock);
> return hwptr_done / (substream->runtime->frame_bits >> 3);
> }
> @@ -858,9 +859,34 @@ static int snd_usb_pcm_prepare(struct snd_pcm_substream *substream)
>
> /* for playback, submit the URBs now; otherwise, the first hwptr_done
> * updates for all URBs would happen at the same time when starting */
> - if (subs->direction == SNDRV_PCM_STREAM_PLAYBACK)
> + if (subs->direction == SNDRV_PCM_STREAM_PLAYBACK) {
> ret = start_endpoints(subs, true);
>
> + /*
> + * Since we submit empty URBS, the constant initial delay will
> + * not be recovered and will be added to the dynamic delay
> + * measured with the frame counter. Worst-case the
> + * startup delay can be (MAX_URBS-1) * MAX_PACKS = 12ms
> + */
> + if (ret == 0) {
> + struct snd_usb_endpoint *ep = subs->data_endpoint;
> + int total_packs = 0;
> + int i;
> +
> + for (i = 0; i < ep->nurbs - 1; i++) {
> + struct snd_urb_ctx *u = &ep->urb[i];
> +
> + total_packs += u->packets;
> + }
> + subs->start_delay = DIV_ROUND_UP(total_packs *
> + subs->cur_rate, 1000);
> + if (subs->start_delay)
> + dev_dbg(&subs->dev->dev,
> + "Initial delay for EP @%p: %d frames\n",
> + ep, subs->start_delay);
> + }
> + }
> +
> unlock:
> snd_usb_unlock_shutdown(subs->stream->chip);
> return ret;
> @@ -1549,6 +1575,7 @@ static void prepare_playback_urb(struct snd_usb_substream *subs,
> runtime->delay = subs->last_delay;
> runtime->delay += frames;
> subs->last_delay = runtime->delay;
> + runtime->delay += subs->start_delay;
>
> /* realign last_frame_number */
> subs->last_frame_number = usb_get_current_frame_number(subs->dev);
> @@ -1597,8 +1624,7 @@ static void retire_playback_urb(struct snd_usb_substream *subs,
> subs->last_delay = 0;
> else
> subs->last_delay -= processed;
> - runtime->delay = subs->last_delay;
> -
> + runtime->delay = subs->last_delay + subs->start_delay;
> /*
> * Report when delay estimate is off by more than 2ms.
> * The error should be lower than 2ms since the estimate relies
> --
> 1.9.1
>
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