X-Git-Url: http://git.tuebingen.mpg.de/?p=paraslash.git;a=blobdiff_plain;f=alsa_write.c;h=3759306ec2215f0732bba5fcc76d18d011db41e1;hp=a3912c1165e6054b0be0bd622b17175fdad4fd8a;hb=bfdd36f2879b8dee1f6d3330bc49fbb5644d3caf;hpb=5cb5db1fbf8f9b96c3b5a1e0cc7de9e710757540

diff --git a/alsa_write.c b/alsa_write.c
index a3912c11..3759306e 100644
--- a/alsa_write.c
+++ b/alsa_write.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2005-2013 Andre Noll <maan@systemlinux.org>
+ * Copyright (C) 2005-2014 Andre Noll <maan@systemlinux.org>
  *
  * Licensed under the GPL v2. For licencing details see COPYING.
  */
@@ -34,17 +34,24 @@ struct private_alsa_write_data {
 	snd_pcm_t *handle;
 	/** Determined and set by alsa_init(). */
 	int bytes_per_frame;
-	/**
-	 * The sample rate given by command line option or the decoder
-	 * of the writer node group.
+	/*
+	 * If the sample rate is not given at the command line and no wav
+	 * header was detected, the btr exec mechanism is employed to query the
+	 * ancestor buffer tree nodes for this information. In a typical setup
+	 * the decoder passes the sample rate back to the alsa writer.
+	 *
+	 *  \sa \ref btr_exec_up().
 	 */
 	unsigned sample_rate;
-	snd_pcm_format_t sample_format;
-	/**
-	 * The number of channels, given by command line option or the
-	 * decoder of the writer node group.
+	/*
+	 * The sample format (8/16 bit, signed/unsigned, little/big endian) is
+	 * determined in the same way as the \a sample_rate.
 	 */
+	snd_pcm_format_t sample_format;
+	/* The number of channels, again determined like \a sample_rate. */
 	unsigned channels;
+	/* time until buffer underrun occurs, in milliseconds */
+	unsigned buffer_time;
 	struct timeval drain_barrier;
 	/* File descriptor for select(). */
 	int poll_fd;
@@ -72,9 +79,9 @@ static int alsa_init(struct private_alsa_write_data *pad,
 	snd_pcm_uframes_t start_threshold, stop_threshold;
 	snd_pcm_uframes_t buffer_size, period_size;
 	snd_output_t *output_log;
-	unsigned buffer_time;
 	int ret;
 	const char *msg;
+	unsigned period_time;
 
 	PARA_INFO_LOG("opening %s\n", conf->device_arg);
 	msg = "unable to open pcm";
@@ -107,18 +114,21 @@ static int alsa_init(struct private_alsa_write_data *pad,
 		&pad->sample_rate, NULL);
 	if (ret < 0)
 		goto fail;
-	msg = "unable to get buffer time";
-	ret = snd_pcm_hw_params_get_buffer_time_max(hwparams, &buffer_time,
-		NULL);
-	if (ret < 0 || buffer_time == 0)
-		goto fail;
-	/* buffer at most 500 milliseconds */
-	buffer_time = PARA_MIN(buffer_time, 500U * 1000U);
+	/* alsa wants microseconds */
+	pad->buffer_time = conf->buffer_time_arg * 1000;
 	msg = "could not set buffer time";
 	ret = snd_pcm_hw_params_set_buffer_time_near(pad->handle, hwparams,
-		&buffer_time, NULL);
+		&pad->buffer_time, NULL);
+	if (ret < 0)
+		goto fail;
+	pad->buffer_time /= 1000; /* we prefer milliseconds */
+	period_time = pad->buffer_time * 250; /* buffer time / 4 */
+	msg = "could not set period time";
+	ret = snd_pcm_hw_params_set_period_time_near(pad->handle, hwparams,
+		&period_time, 0);
 	if (ret < 0)
 		goto fail;
+
 	msg = "unable to install hw params";
 	ret = snd_pcm_hw_params(pad->handle, hwparams);
 	if (ret < 0)
@@ -166,15 +176,16 @@ static int alsa_init(struct private_alsa_write_data *pad,
 	if (ret == 0) {
 		char *buf, *p;
 		size_t sz;
-		PARA_INFO_LOG("dumping alsa configuration\n");
+		PARA_DEBUG_LOG("dumping alsa configuration\n");
 		snd_pcm_dump(pad->handle, output_log);
+		snd_pcm_hw_params_dump(hwparams, output_log);
 		sz = snd_output_buffer_string(output_log, &buf);
 		for (p = buf; p < buf + sz;) {
 			char *q = memchr(p, '\n', buf + sz - p);
 			if (!q)
 				break;
 			*q = '\0';
-			PARA_INFO_LOG("%s\n", p);
+			PARA_DEBUG_LOG("%s\n", p);
 			p = q + 1;
 		}
 		snd_output_close(output_log);
@@ -207,11 +218,12 @@ static void alsa_write_pre_select(struct sched *s, struct task *t)
 		sched_request_barrier_or_min_delay(&pad->drain_barrier, s);
 		return;
 	}
+	/* wait at most 50% of the buffer time */
+	sched_request_timeout_ms(pad->buffer_time / 2, s);
 	ret = snd_pcm_poll_descriptors(pad->handle, &pfd, 1);
 	if (ret < 0) {
 		PARA_ERROR_LOG("could not get alsa poll fd: %s\n",
 			snd_strerror(-ret));
-		t->error = -E_ALSA;
 		return;
 	}
 	pad->poll_fd = pfd.fd;
@@ -296,21 +308,13 @@ again:
 		wn->min_iqs = pad->bytes_per_frame;
 		goto again;
 	}
-	if (pad->poll_fd < 0 || !FD_ISSET(pad->poll_fd, &s->rfds))
-		return 0;
 	frames = bytes / pad->bytes_per_frame;
 	frames = snd_pcm_writei(pad->handle, data, frames);
 	if (frames == 0 || frames == -EAGAIN) {
-		/*
-		 * The alsa poll fd was ready for IO but we failed to write to
-		 * the alsa handle. This means another event is pending. We
-		 * don't care about that but we have to dispatch the event in
-		 * order to avoid a busy loop. So we simply read from the poll
-		 * fd.
-		 */
 		char buf[100];
-		if (read(pad->poll_fd, buf, 100))
-			do_nothing;
+		if (pad->poll_fd >= 0 && FD_ISSET(pad->poll_fd, &s->rfds))
+			if (read(pad->poll_fd, buf, 100))
+				do_nothing;
 		return 0;
 	}
 	if (frames > 0) {