[alsa-devel] [PATCH] improved snd-aloop quality when using certain samplerates and kernel HZ

[Ahmet İnan]

after using a HZ:=300 kernel for some time now and needing snd-aloop again i
found out, that i either had to correct the hardcoded number, or fix the
problem permanently, which couses stuttering and other problems.

i also removed the SYNC on start code, not just because its more or less
useless and brings problems, but ive got a nice idea how to fix this
overrun/underrun problem in a much nicer way.

so stay tuned for the next patch, until its implemented.

this patch here is more or less experimental, id like to hear some feedback.

http://www.mathematik.uni-freiburg.de/IAM/homepages/ainan/alsa-driver-1.0.15-aloop-ainan-patch0.diff

Signed-off-by: Ahmet İnan <ainan <at> mathematik.uni-freiburg.de>

please also include my email address when responding - i have no intention
to enable recieving emails from the list.

ahmet

--
admin der abteilung für angewandte mathematik, tel. 0761-203-5626
-------------- next part --------------
--- aloop-kernel-orig.c	2008-02-19 03:27:10.203115360 +0100
+++ aloop-kernel.c	2008-02-19 03:23:56.874121702 +0100
@@ -32,9 +32,6 @@
 
 /* comment in to trash your kernel logfiles */
 /* #define SND_CARD_LOOPBACK_VERBOSE */
-/* comment in for synchronization on start trigger
- * works well on alsa apps but bad on oss emulation */
-/* #define SND_CARD_LOOPBACK_START_SYNC */
 
 MODULE_AUTHOR("Jaroslav Kysela <perex at perex.cz>");
 MODULE_DESCRIPTION("A loopback soundcard");
@@ -85,16 +82,13 @@
 	snd_card_loopback_t *loopback;
 	spinlock_t lock;
 	struct timer_list timer;
-	int stream;
-	unsigned int pcm_1000_size;
-	unsigned int pcm_1000_count;
-	unsigned int pcm_size;
-	unsigned int pcm_count;
+	unsigned int pcm_size_hz;
+	unsigned int pcm_count_hz;
 	unsigned int pcm_bps;		/* bytes per second */
-	unsigned int pcm_1000_jiffie;	/* 1000 * bytes per one jiffie */
-	unsigned int pcm_1000_irq_pos;	/* IRQ position */
-	unsigned int pcm_1000_buf_pos;	/* position in buffer */
-	unsigned int pcm_period_pos;	/* period aligned pos in buffer */
+	unsigned int pcm_hz;		/* HZ */
+	unsigned int pcm_irq_pos_hz;	/* IRQ position * HZ */
+	unsigned int pcm_buf_pos_hz;	/* position in buffer * HZ */
+	unsigned int pcm_period_pos_hz;	/* period aligned pos in buffer * HZ */
 	struct snd_pcm_substream *substream;
 	struct snd_card_loopback_cable *cable;
 } snd_card_loopback_pcm_t;
@@ -123,18 +117,7 @@
 {
 	struct snd_pcm_runtime *runtime = substream->runtime;
 	snd_card_loopback_pcm_t *dpcm = runtime->private_data;
-#ifdef SND_CARD_LOOPBACK_START_SYNC
-	snd_card_loopback_pcm_t *capture_dpcm;
-#endif
 	if (cmd == SNDRV_PCM_TRIGGER_START) {
-#ifdef SND_CARD_LOOPBACK_START_SYNC
-		if (dpcm->cable->capture_running) {
-			capture_dpcm = dpcm->cable->capture->runtime->private_data;
-			dpcm->pcm_1000_irq_pos = capture_dpcm->pcm_1000_irq_pos;
-			dpcm->pcm_1000_buf_pos = capture_dpcm->pcm_1000_buf_pos;
-			dpcm->pcm_period_pos = capture_dpcm->pcm_period_pos;
-		}
-#endif
 		dpcm->cable->playback_running = 1;
 		snd_card_loopback_timer_start(substream);
 	} else if (cmd == SNDRV_PCM_TRIGGER_STOP) {
@@ -154,18 +137,7 @@
 {
 	struct snd_pcm_runtime *runtime = substream->runtime;
 	snd_card_loopback_pcm_t *dpcm = runtime->private_data;
-#ifdef SND_CARD_LOOPBACK_START_SYNC
-	snd_card_loopback_pcm_t *playback_dpcm;
-#endif
 	if (cmd == SNDRV_PCM_TRIGGER_START) {
-#ifdef SND_CARD_LOOPBACK_START_SYNC
-		if (dpcm->cable->playback_running) {
-			playback_dpcm = dpcm->cable->playback->runtime->private_data;
-			dpcm->pcm_1000_irq_pos = playback_dpcm->pcm_1000_irq_pos;
-			dpcm->pcm_1000_buf_pos = playback_dpcm->pcm_1000_buf_pos;
-			dpcm->pcm_period_pos = playback_dpcm->pcm_period_pos;
-		}
-#endif
 		dpcm->cable->capture_running = 1;
 		snd_card_loopback_timer_start(substream);
 	} else if (cmd == SNDRV_PCM_TRIGGER_STOP) {
@@ -190,14 +162,12 @@
 	if (bps <= 0)
 		return -EINVAL;
 	dpcm->pcm_bps = bps;
-	dpcm->pcm_1000_jiffie = (1000 * bps) / HZ;
-	dpcm->pcm_size = frames_to_bytes(runtime, runtime->buffer_size);
-	dpcm->pcm_count = frames_to_bytes(runtime, runtime->period_size);
-	dpcm->pcm_1000_size = 1000 * frames_to_bytes(runtime, runtime->buffer_size);
-	dpcm->pcm_1000_count = 1000 * frames_to_bytes(runtime, runtime->period_size);
-	dpcm->pcm_1000_irq_pos = 0;
-	dpcm->pcm_1000_buf_pos = 0;
-	dpcm->pcm_period_pos = 0;
+	dpcm->pcm_hz = HZ;
+	dpcm->pcm_size_hz = frames_to_bytes(runtime, runtime->buffer_size) * dpcm->pcm_hz;
+	dpcm->pcm_count_hz = frames_to_bytes(runtime, runtime->period_size) * dpcm->pcm_hz;
+	dpcm->pcm_irq_pos_hz = 0;
+	dpcm->pcm_buf_pos_hz = 0;
+	dpcm->pcm_period_pos_hz = 0;
 
 	cable->hw.formats = (1ULL << runtime->format);
 	cable->hw.rate_min = runtime->rate;
@@ -246,13 +216,13 @@
 	add_timer(&dpcm->timer);
 	spin_lock_irq(&dpcm->lock);
 
-	dpcm->pcm_1000_irq_pos += dpcm->pcm_1000_jiffie;
-	dpcm->pcm_1000_buf_pos += dpcm->pcm_1000_jiffie;
-	dpcm->pcm_1000_buf_pos %= dpcm->pcm_1000_size;
-	if (dpcm->pcm_1000_irq_pos >= dpcm->pcm_1000_count) {
-		dpcm->pcm_1000_irq_pos %= dpcm->pcm_1000_count;
-		dpcm->pcm_period_pos += dpcm->pcm_count;
-		dpcm->pcm_period_pos %= dpcm->pcm_size;
+	dpcm->pcm_irq_pos_hz += dpcm->pcm_bps;
+	dpcm->pcm_buf_pos_hz += dpcm->pcm_bps;
+	dpcm->pcm_buf_pos_hz %= dpcm->pcm_size_hz;
+	if (dpcm->pcm_irq_pos_hz >= dpcm->pcm_count_hz) {
+		dpcm->pcm_irq_pos_hz %= dpcm->pcm_count_hz;
+		dpcm->pcm_period_pos_hz += dpcm->pcm_count_hz;
+		dpcm->pcm_period_pos_hz %= dpcm->pcm_size_hz;
 		spin_unlock_irq(&dpcm->lock);	
 		snd_pcm_period_elapsed(dpcm->substream);
 	} else {
@@ -264,7 +234,7 @@
 {
 	struct snd_pcm_runtime *runtime = substream->runtime;
 	snd_card_loopback_pcm_t *dpcm = runtime->private_data;
-	return bytes_to_frames(runtime, dpcm->pcm_period_pos);
+	return bytes_to_frames(runtime, dpcm->pcm_period_pos_hz / dpcm->pcm_hz);
 }
 
 static struct snd_pcm_hardware snd_card_loopback_info =
@@ -381,7 +351,6 @@
 	dpcm->timer.data = (unsigned long)dpcm;
 	dpcm->timer.function = snd_card_loopback_timer_function;
 	dpcm->cable = &loopback->cables[substream->number][half];
-	dpcm->stream = substream->stream;
 	runtime->private_data = dpcm;
 	runtime->private_free = snd_card_loopback_runtime_free;
 	runtime->hw = snd_card_loopback_info;