X-Git-Url: http://git.tuebingen.mpg.de/?p=paraslash.git;a=blobdiff_plain;f=alsa_write.c;h=679962e0e00f276700138bb83517e7fbd7ab8bb7;hp=ae8bed6d339724563e86eb899d9aa96a46f6f8e7;hb=702d72b58b6378c4cdb37cbb709fd1d351571123;hpb=57b7c4c20305a1b64e7a2141a90cfdc96956d1fc

diff --git a/alsa_write.c b/alsa_write.c
index ae8bed6d..679962e0 100644
--- a/alsa_write.c
+++ b/alsa_write.c
@@ -36,10 +36,10 @@ struct private_alsa_write_data {
 	snd_pcm_t *handle;
 	/** Determined and set by alsa_open(). */
 	int bytes_per_frame;
-	/** Don't write anything until this time. */
-	struct timeval next_chunk;
 	/** The approximate maximum buffer duration in us. */
 	unsigned buffer_time;
+	/* Number of frames that fit into the buffer. */
+	unsigned buffer_frames;
 	/**
 	 * The samplerate given by command line option or the decoder
 	 * of the writer node group.
@@ -120,6 +120,8 @@ static int alsa_init(struct private_alsa_write_data *pad,
 	PARA_INFO_LOG("bytes per frame: %d\n", pad->bytes_per_frame);
 	if (snd_pcm_nonblock(pad->handle, 1))
 		PARA_ERROR_LOG("failed to set nonblock mode\n");
+	pad->buffer_frames = 1000 * pad->buffer_time / pad->samplerate;
+	PARA_INFO_LOG("max buffered frames: %d\n", pad->buffer_frames);
 	return 1;
 }
 
@@ -140,7 +142,6 @@ static int alsa_open(struct writer_node *wn)
 	else
 		pad->channels = conf->channels_arg;
 	PARA_INFO_LOG("%d channel(s), %dHz\n", pad->channels, pad->samplerate);
-	tv_add(now, &(struct timeval){0, 100 * 1000}, &pad->next_chunk);
 	return 1;
 }
 
@@ -148,17 +149,34 @@ static int alsa_write_pre_select(struct sched *s, struct writer_node *wn)
 {
 	struct private_alsa_write_data *pad = wn->private_data;
 	struct writer_node_group *wng = wn->wng;
-	struct timeval diff;
+	struct timeval tv;
+	snd_pcm_sframes_t avail, underrun;
 
-	if (!*wng->loaded)
+	if (!pad->handle)
 		return 1;
-	if (tv_diff(now, &pad->next_chunk, &diff) < 0) {
-		if (tv_diff(&s->timeout, &diff, NULL) > 0)
-			s->timeout = diff;
-	} else {
-		s->timeout.tv_sec = 0;
-		s->timeout.tv_usec = 1;
-	}
+	if (*wng->loaded - wn->written < pad->bytes_per_frame)
+		return 1;
+	/*
+	 * Data is available to be written to the alsa handle.  Compute number
+	 * of milliseconds until next buffer underrun would occur.
+	 *
+	 * snd_pcm_avail_update() updates the current available count of
+	 * samples for writing.  It is a light method to obtain current stream
+	 * position, because it does not require the user <-> kernel context
+	 * switch, but the value is less accurate, because ring buffer pointers
+	 * are updated in kernel drivers only when an interrupt occurs.
+	 */
+	avail = snd_pcm_avail_update(pad->handle);
+	if (avail < 0)
+		avail = 0;
+	underrun = (pad->buffer_frames - avail) * pad->buffer_time
+		/ pad->buffer_frames / 1000;
+	if (underrun < 50)
+		underrun = 50;
+	underrun -= 50;
+	ms2tv(underrun, &tv);
+	if (tv_diff(&s->timeout, &tv, NULL) > 0)
+		s->timeout = tv;
 	return 1;
 }
 
@@ -169,7 +187,6 @@ static int alsa_write_post_select(__a_unused struct sched *s,
 	struct writer_node_group *wng = wn->wng;
 	size_t bytes = *wng->loaded - wn->written;
 	unsigned char *data = (unsigned char*)*wng->bufp + wn->written;
-	struct timeval tv;
 	snd_pcm_sframes_t ret, frames, avail;
 
 	if (*wng->input_error < 0 && (!pad->handle || bytes < pad->bytes_per_frame)) {
@@ -178,8 +195,6 @@ static int alsa_write_post_select(__a_unused struct sched *s,
 	}
 	if (!bytes) /* no data available */
 		return 0;
-	if (tv_diff(now, &pad->next_chunk, NULL) < 0)
-		return 0;
 	if (!pad->handle) {
 		int err = alsa_init(pad, wn->conf);
 		if (err < 0)
@@ -190,26 +205,21 @@ static int alsa_write_post_select(__a_unused struct sched *s,
 		return 0;
 	avail = snd_pcm_avail_update(pad->handle);
 	if (avail <= 0)
-		goto delay;
+		return 0;
 	frames = PARA_MIN(frames, avail);
 	ret = snd_pcm_writei(pad->handle, data, frames);
-	if (ret < 0) {
-		PARA_WARNING_LOG("%s\n", snd_strerror(-ret));
-		if (ret == -EPIPE) {
-			snd_pcm_prepare(pad->handle);
-			return 0;
-		}
-		if (ret == -EAGAIN)
-			goto delay;
-		return -E_ALSA_WRITE;
+	if (ret >= 0) {
+		wn->written += ret * pad->bytes_per_frame;
+		return 1;
 	}
-	wn->written += ret * pad->bytes_per_frame;
-	return 1;
-delay:
-	/* wait until 50% buffer space is available */
-	ms2tv(pad->buffer_time / 2000, &tv);
-	tv_add(now, &tv, &pad->next_chunk);
-	return 0;
+	PARA_WARNING_LOG("%s\n", snd_strerror(-ret));
+	if (ret == -EPIPE) {
+		snd_pcm_prepare(pad->handle);
+		return 0;
+	}
+	if (ret == -EAGAIN)
+		return 0;
+	return -E_ALSA_WRITE;
 }
 
 static void alsa_close(struct writer_node *wn)