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-rw-r--r--sound/usb/pcm.c29
1 files changed, 26 insertions, 3 deletions
diff --git a/sound/usb/pcm.c b/sound/usb/pcm.c
index 1546577ae458..5ceb8f1d63fb 100644
--- a/sound/usb/pcm.c
+++ b/sound/usb/pcm.c
@@ -1091,7 +1091,16 @@ static void prepare_playback_urb(struct snd_usb_substream *subs,
subs->hwptr_done += bytes;
if (subs->hwptr_done >= runtime->buffer_size * stride)
subs->hwptr_done -= runtime->buffer_size * stride;
+
+ /* update delay with exact number of samples queued */
+ runtime->delay = subs->last_delay;
runtime->delay += frames;
+ subs->last_delay = runtime->delay;
+
+ /* realign last_frame_number */
+ subs->last_frame_number = usb_get_current_frame_number(subs->dev);
+ subs->last_frame_number &= 0xFF; /* keep 8 LSBs */
+
spin_unlock_irqrestore(&subs->lock, flags);
urb->transfer_buffer_length = bytes;
if (period_elapsed)
@@ -1109,12 +1118,26 @@ static void retire_playback_urb(struct snd_usb_substream *subs,
struct snd_pcm_runtime *runtime = subs->pcm_substream->runtime;
int stride = runtime->frame_bits >> 3;
int processed = urb->transfer_buffer_length / stride;
+ int est_delay;
spin_lock_irqsave(&subs->lock, flags);
- if (processed > runtime->delay)
- runtime->delay = 0;
+ est_delay = snd_usb_pcm_delay(subs, runtime->rate);
+ /* update delay with exact number of samples played */
+ if (processed > subs->last_delay)
+ subs->last_delay = 0;
else
- runtime->delay -= processed;
+ subs->last_delay -= processed;
+ runtime->delay = subs->last_delay;
+
+ /*
+ * Report when delay estimate is off by more than 2ms.
+ * The error should be lower than 2ms since the estimate relies
+ * on two reads of a counter updated every ms.
+ */
+ if (abs(est_delay - subs->last_delay) * 1000 > runtime->rate * 2)
+ snd_printk(KERN_DEBUG "delay: estimated %d, actual %d\n",
+ est_delay, subs->last_delay);
+
spin_unlock_irqrestore(&subs->lock, flags);
}