From: Andre Noll <maan@systemlinux.org>
Date: Sun, 3 May 2009 16:11:22 +0000 (+0200)
Subject: Alsa fixes and cleanups.
X-Git-Tag: v0.3.4~5
X-Git-Url: http://git.tue.mpg.de/?a=commitdiff_plain;h=9b5d9adba31e6d42b9dde81fcd3b6f8a0b16bcfc;p=paraslash.git

Alsa fixes and cleanups.

This patch

- replaces the unused E_SND_PCM_INFO error by E_PHYSICAL_WIDTH,

- checks the return value of snd_pcm_format_physical_width() and returns
  -E_PHYSICAL_WIDTH if this causes bytes_per_frame being non-positive,

- introduces an upper bound for the start threshold. Without that
  change, playback could be delayed by several seconds on some alsa
  configurations (problem pointed out by Johannes Wörner, thanks).

- does not return early on input errors which could cause the last
  part of the audio stream being skipped.

- avoids calling snd_pcm_writei() with a frame count of zero which
  could happen with the old code in case there's more than zero but
  less than a full frame of audio data available.

- cleans up the documentation of struct private_alsa_write_data
---

diff --git a/alsa_write.c b/alsa_write.c
index e070399d..0bb3de38 100644
--- a/alsa_write.c
+++ b/alsa_write.c
@@ -29,19 +29,19 @@
 /** always use 16 bit little endian */
 #define FORMAT SND_PCM_FORMAT_S16_LE
 
-/** data specific to the alsa writer */
+/** Data specific to the alsa writer. */
 struct private_alsa_write_data {
-	/** the alsa handle */
+	/** The alsa handle */
 	snd_pcm_t *handle;
-	/** determined and set by alsa_open() */
-	size_t bytes_per_frame;
-	/** don't write anything until this time */
+	/** Determined and set by alsa_open(). */
+	int bytes_per_frame;
+	/** Don't write anything until this time. */
 	struct timeval next_chunk;
-	/** the return value of snd_pcm_hw_params_get_buffer_time_max() */
+	/** The approximate maximum buffer duration in us. */
 	unsigned buffer_time;
 	/**
-	 * the samplerate given by command line option or the decoder
-	 * of the writer node group
+	 * The samplerate given by command line option or the decoder
+	 * of the writer node group.
 	 */
 	unsigned samplerate;
 	/**
@@ -101,7 +101,8 @@ static int alsa_init(struct private_alsa_write_data *pad,
 	if (buffer_size < 1)
 		start_threshold = 1;
 	else
-		start_threshold = buffer_size;
+		start_threshold = PARA_MIN(buffer_size,
+			(snd_pcm_uframes_t)pad->samplerate);
 	if (snd_pcm_sw_params_set_start_threshold(pad->handle, swparams,
 			start_threshold) < 0)
 		return -E_START_THRESHOLD;
@@ -113,6 +114,8 @@ static int alsa_init(struct private_alsa_write_data *pad,
 		PARA_WARNING_LOG("unable to install sw params\n");
 	pad->bytes_per_frame = snd_pcm_format_physical_width(FORMAT)
 		* pad->channels / 8;
+	if (pad->bytes_per_frame <= 0)
+		return -E_PHYSICAL_WIDTH;
 	PARA_INFO_LOG("bytes per frame: %zu\n", pad->bytes_per_frame);
 	if (snd_pcm_nonblock(pad->handle, 1))
 		PARA_ERROR_LOG("failed to set nonblock mode\n");
@@ -168,6 +171,10 @@ static int alsa_write_post_select(__a_unused struct sched *s,
 	struct timeval tv;
 	snd_pcm_sframes_t ret;
 
+	if (*wng->input_error < 0 && (!pad->handle || bytes < pad->bytes_per_frame)) {
+		wn->written = *wng->loaded;
+		return *wng->input_error;
+	}
 	if (!bytes) /* no data available */
 		goto out;
 	if (tv_diff(now, &pad->next_chunk, NULL) < 0)
@@ -178,6 +185,8 @@ static int alsa_write_post_select(__a_unused struct sched *s,
 			return err;
 	}
 	frames = bytes / pad->bytes_per_frame;
+	if (!frames) /* less than a single frame available */
+		goto out;
 	ret = snd_pcm_writei(pad->handle, data, frames);
 	if (ret == -EPIPE) {
 		PARA_WARNING_LOG("EPIPE\n");
@@ -195,15 +204,11 @@ static int alsa_write_post_select(__a_unused struct sched *s,
 		wn->written += ret * pad->bytes_per_frame;
 	if (ret == frames) /* we wrote everything, try again immediately */
 		pad->next_chunk	= *now;
-	else {
-		ms2tv(pad->buffer_time / pad->bytes_per_frame / 1000, &tv);
+	else { /* wait until 50% buffer space is available */
+		ms2tv(pad->buffer_time / 2000, &tv);
 		tv_add(now, &tv, &pad->next_chunk);
 	}
 out:
-	if (*wng->input_error < 0) {
-		wn->written = *wng->loaded;
-		return *wng->input_error;
-	}
 	return 1;
 }
 
diff --git a/error.h b/error.h
index 17f3703f..60415223 100644
--- a/error.h
+++ b/error.h
@@ -396,7 +396,7 @@ extern const char **para_errlist[];
 	PARA_ERROR(BAD_PERIOD, "can not use period equal to buffer size"), \
 	PARA_ERROR(ALSA_WRITE, "alsa write error"), \
 	PARA_ERROR(PCM_OPEN, "unable to open pcm"), \
-	PARA_ERROR(SND_PCM_INFO, "pcm info error"), \
+	PARA_ERROR(PHYSICAL_WIDTH, "unable to determine bytes per frame"), \
 	PARA_ERROR(GET_BUFFER_TIME, "snd_pcm_hw_params_get_buffer_time_max() failed"), \
 	PARA_ERROR(SET_BUFFER_TIME, "snd_pcm_hw_params_set_buffer_time_near() failed"), \
 	PARA_ERROR(SET_RATE, "snd_pcm_hw_params_set_rate_near failed"), \