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-rw-r--r--sound/usb/card.h2
-rw-r--r--sound/usb/pcm.c28
-rw-r--r--sound/usb/pcm.h3
-rw-r--r--sound/usb/urb.c30
4 files changed, 60 insertions, 3 deletions
diff --git a/sound/usb/card.h b/sound/usb/card.h
index ae4251d..a39edcc 100644
--- a/sound/usb/card.h
+++ b/sound/usb/card.h
@@ -94,6 +94,8 @@ struct snd_usb_substream {
spinlock_t lock;
struct snd_urb_ops ops; /* callbacks (must be filled at init) */
+ int last_frame_number; /* stored frame number */
+ int last_delay; /* stored delay */
};
struct snd_usb_stream {
diff --git a/sound/usb/pcm.c b/sound/usb/pcm.c
index b8dcbf4..0b699ca 100644
--- a/sound/usb/pcm.c
+++ b/sound/usb/pcm.c
@@ -34,6 +34,30 @@
#include "clock.h"
#include "power.h"
+/* return the estimated delay based on USB frame counters */
+snd_pcm_uframes_t snd_usb_pcm_delay(struct snd_usb_substream *subs,
+ unsigned int rate)
+{
+ int current_frame_number;
+ int frame_diff;
+ int est_delay;
+
+ current_frame_number = usb_get_current_frame_number(subs->dev);
+ /*
+ * HCD implementations use different widths, use lower 8 bits.
+ * The delay will be managed up to 256ms, which is more than
+ * enough
+ */
+ frame_diff = (current_frame_number - subs->last_frame_number) & 0xff;
+
+ /* Approximation based on number of samples per USB frame (ms),
+ some truncation for 44.1 but the estimate is good enough */
+ est_delay = subs->last_delay - (frame_diff * rate / 1000);
+ if (est_delay < 0)
+ est_delay = 0;
+ return est_delay;
+}
+
/*
* return the current pcm pointer. just based on the hwptr_done value.
*/
@@ -45,6 +69,8 @@ static snd_pcm_uframes_t snd_usb_pcm_pointer(struct snd_pcm_substream *substream
subs = (struct snd_usb_substream *)substream->runtime->private_data;
spin_lock(&subs->lock);
hwptr_done = subs->hwptr_done;
+ substream->runtime->delay = snd_usb_pcm_delay(subs,
+ substream->runtime->rate);
spin_unlock(&subs->lock);
return hwptr_done / (substream->runtime->frame_bits >> 3);
}
@@ -417,6 +443,8 @@ static int snd_usb_pcm_prepare(struct snd_pcm_substream *substream)
subs->hwptr_done = 0;
subs->transfer_done = 0;
subs->phase = 0;
+ subs->last_delay = 0;
+ subs->last_frame_number = 0;
runtime->delay = 0;
return snd_usb_substream_prepare(subs, runtime);
diff --git a/sound/usb/pcm.h b/sound/usb/pcm.h
index ed3e283..df7a003 100644
--- a/sound/usb/pcm.h
+++ b/sound/usb/pcm.h
@@ -1,6 +1,9 @@
#ifndef __USBAUDIO_PCM_H
#define __USBAUDIO_PCM_H
+snd_pcm_uframes_t snd_usb_pcm_delay(struct snd_usb_substream *subs,
+ unsigned int rate);
+
void snd_usb_set_pcm_ops(struct snd_pcm *pcm, int stream);
int snd_usb_init_pitch(struct snd_usb_audio *chip, int iface,
diff --git a/sound/usb/urb.c b/sound/usb/urb.c
index e184349..b4dcccc 100644
--- a/sound/usb/urb.c
+++ b/sound/usb/urb.c
@@ -718,7 +718,16 @@ static int 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)
@@ -737,12 +746,27 @@ static int retire_playback_urb(struct snd_usb_substream *subs,
unsigned long flags;
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);
return 0;
}
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