[alsa-devel] PCM delay compensation

[Takashi Iwai]

Hi,

the patch below (to the latest sound git tree) adds the extra delay
count for USB-audio driver.  This change will appear as the return
value of snd_pcm_delay().

Could you check whether it's appropriate behavior you've wanted?


thanks,

Takashi

diff --git a/include/sound/pcm.h b/include/sound/pcm.h
index 40c5a6f..dcbdc60 100644
--- a/include/sound/pcm.h
+++ b/include/sound/pcm.h
@@ -269,6 +269,7 @@ struct snd_pcm_runtime {
 	snd_pcm_uframes_t avail_max;
 	snd_pcm_uframes_t hw_ptr_base;	/* Position at buffer restart */
 	snd_pcm_uframes_t hw_ptr_interrupt; /* Position at interrupt time*/
+	snd_pcm_sframes_t delay;	/* extra delay; typically FIFO size */
 
 	/* -- HW params -- */
 	snd_pcm_access_t access;	/* access mode */
diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
index e61e125..df7c3fa 100644
--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -597,14 +597,15 @@ int snd_pcm_status(struct snd_pcm_substream *substream,
 	if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK) {
 		status->avail = snd_pcm_playback_avail(runtime);
 		if (runtime->status->state == SNDRV_PCM_STATE_RUNNING ||
-		    runtime->status->state == SNDRV_PCM_STATE_DRAINING)
+		    runtime->status->state == SNDRV_PCM_STATE_DRAINING) {
 			status->delay = runtime->buffer_size - status->avail;
-		else
+			status->delay += runtime->delay;
+		} else
 			status->delay = 0;
 	} else {
 		status->avail = snd_pcm_capture_avail(runtime);
 		if (runtime->status->state == SNDRV_PCM_STATE_RUNNING)
-			status->delay = status->avail;
+			status->delay = status->avail + runtime->delay;
 		else
 			status->delay = 0;
 	}
@@ -2423,6 +2424,7 @@ static int snd_pcm_delay(struct snd_pcm_substream *substream,
 			n = snd_pcm_playback_hw_avail(runtime);
 		else
 			n = snd_pcm_capture_avail(runtime);
+		n += runtime->delay;
 		break;
 	case SNDRV_PCM_STATE_XRUN:
 		err = -EPIPE;
diff --git a/sound/usb/usbaudio.c b/sound/usb/usbaudio.c
index 6e70ba4..7d5a103 100644
--- a/sound/usb/usbaudio.c
+++ b/sound/usb/usbaudio.c
@@ -629,6 +629,7 @@ static int prepare_playback_urb(struct snd_usb_substream *subs,
 	subs->hwptr_done += offs;
 	if (subs->hwptr_done >= runtime->buffer_size)
 		subs->hwptr_done -= runtime->buffer_size;
+	runtime->delay += offs;
 	spin_unlock_irqrestore(&subs->lock, flags);
 	urb->transfer_buffer_length = offs * stride;
 	if (period_elapsed)
@@ -638,12 +639,20 @@ static int prepare_playback_urb(struct snd_usb_substream *subs,
 
 /*
  * process after playback data complete
- * - nothing to do
+ * - decrease the delay count again
  */
 static int retire_playback_urb(struct snd_usb_substream *subs,
 			       struct snd_pcm_runtime *runtime,
 			       struct urb *urb)
 {
+	unsigned long flags;
+	int stride = runtime->frame_bits >> 3;
+	int processed = urb->transfer_buffer_length / stride;
+
+	spin_lock_irqsave(&subs->lock, flags);
+	if (processed > runtime->delay)
+		runtime->delay -= processed;
+	spin_unlock_irqrestore(&subs->lock, flags);
 	return 0;
 }
 
@@ -1542,6 +1551,7 @@ static int snd_usb_pcm_prepare(struct snd_pcm_substream *substream)
 	subs->hwptr_done = 0;
 	subs->transfer_done = 0;
 	subs->phase = 0;
+	runtime->delay = 0;
 
 	/* clear urbs (to be sure) */
 	deactivate_urbs(subs, 0, 1);