On Fri, 30 Sep 2016 14:43:30 +0200, Subhransu S. Prusty wrote:
From: Pierre-Louis Bossart pierre-louis.bossart@linux.intel.com
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@intel.com Signed-off-by: Pierre-Louis Bossart pierre-louis.bossart@linux.intel.com Signed-off-by: Subhransu S. Prusty subhransu.s.prusty@intel.com
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