ALSA: snd-aloop - improve the sample copy accurracy
Maintain both streams (playback, capture) synchronized. Previous code
didn't take in account the small byte count drifts caused by the irq
position rounding.
Signed-off-by: Jaroslav Kysela <perex@perex.cz>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
diff --git a/sound/drivers/aloop.c b/sound/drivers/aloop.c
index ad079b6..8b5c36f 100644
--- a/sound/drivers/aloop.c
+++ b/sound/drivers/aloop.c
@@ -117,6 +117,7 @@
/* timer stuff */
unsigned int irq_pos; /* fractional IRQ position */
unsigned int period_size_frac;
+ unsigned int last_drift;
unsigned long last_jiffies;
struct timer_list timer;
};
@@ -264,6 +265,7 @@
return err;
dpcm->last_jiffies = jiffies;
dpcm->pcm_rate_shift = 0;
+ dpcm->last_drift = 0;
spin_lock(&cable->lock);
cable->running |= stream;
cable->pause &= ~stream;
@@ -444,34 +446,30 @@
}
}
-#define BYTEPOS_UPDATE_POSONLY 0
-#define BYTEPOS_UPDATE_CLEAR 1
-#define BYTEPOS_UPDATE_COPY 2
-
-static void loopback_bytepos_update(struct loopback_pcm *dpcm,
- unsigned int delta,
- unsigned int cmd)
+static inline unsigned int bytepos_delta(struct loopback_pcm *dpcm,
+ unsigned int jiffies_delta)
{
- unsigned int count;
unsigned long last_pos;
+ unsigned int delta;
last_pos = byte_pos(dpcm, dpcm->irq_pos);
- dpcm->irq_pos += delta * dpcm->pcm_bps;
- count = byte_pos(dpcm, dpcm->irq_pos) - last_pos;
- if (!count)
- return;
- if (cmd == BYTEPOS_UPDATE_CLEAR)
- clear_capture_buf(dpcm, count);
- else if (cmd == BYTEPOS_UPDATE_COPY)
- copy_play_buf(dpcm->cable->streams[SNDRV_PCM_STREAM_PLAYBACK],
- dpcm->cable->streams[SNDRV_PCM_STREAM_CAPTURE],
- count);
- dpcm->buf_pos += count;
- dpcm->buf_pos %= dpcm->pcm_buffer_size;
+ dpcm->irq_pos += jiffies_delta * dpcm->pcm_bps;
+ delta = byte_pos(dpcm, dpcm->irq_pos) - last_pos;
+ if (delta >= dpcm->last_drift)
+ delta -= dpcm->last_drift;
+ dpcm->last_drift = 0;
if (dpcm->irq_pos >= dpcm->period_size_frac) {
dpcm->irq_pos %= dpcm->period_size_frac;
dpcm->period_update_pending = 1;
}
+ return delta;
+}
+
+static inline void bytepos_finish(struct loopback_pcm *dpcm,
+ unsigned int delta)
+{
+ dpcm->buf_pos += delta;
+ dpcm->buf_pos %= dpcm->pcm_buffer_size;
}
static unsigned int loopback_pos_update(struct loopback_cable *cable)
@@ -481,7 +479,7 @@
struct loopback_pcm *dpcm_capt =
cable->streams[SNDRV_PCM_STREAM_CAPTURE];
unsigned long delta_play = 0, delta_capt = 0;
- unsigned int running;
+ unsigned int running, count1, count2;
unsigned long flags;
spin_lock_irqsave(&cable->lock, flags);
@@ -500,12 +498,13 @@
goto unlock;
if (delta_play > delta_capt) {
- loopback_bytepos_update(dpcm_play, delta_play - delta_capt,
- BYTEPOS_UPDATE_POSONLY);
+ count1 = bytepos_delta(dpcm_play, delta_play - delta_capt);
+ bytepos_finish(dpcm_play, count1);
delta_play = delta_capt;
} else if (delta_play < delta_capt) {
- loopback_bytepos_update(dpcm_capt, delta_capt - delta_play,
- BYTEPOS_UPDATE_CLEAR);
+ count1 = bytepos_delta(dpcm_capt, delta_capt - delta_play);
+ clear_capture_buf(dpcm_capt, count1);
+ bytepos_finish(dpcm_capt, count1);
delta_capt = delta_play;
}
@@ -513,8 +512,17 @@
goto unlock;
/* note delta_capt == delta_play at this moment */
- loopback_bytepos_update(dpcm_capt, delta_capt, BYTEPOS_UPDATE_COPY);
- loopback_bytepos_update(dpcm_play, delta_play, BYTEPOS_UPDATE_POSONLY);
+ count1 = bytepos_delta(dpcm_play, delta_play);
+ count2 = bytepos_delta(dpcm_capt, delta_capt);
+ if (count1 < count2) {
+ dpcm_capt->last_drift = count2 - count1;
+ count1 = count2;
+ } else if (count1 > count2) {
+ dpcm_play->last_drift = count1 - count2;
+ }
+ copy_play_buf(dpcm_play, dpcm_capt, count1);
+ bytepos_finish(dpcm_play, count1);
+ bytepos_finish(dpcm_capt, count1);
unlock:
spin_unlock_irqrestore(&cable->lock, flags);
return running;