-/*
- * This file is part of DisOrder.
- * Copyright (C) 2008 Richard Kettlewell
- *
- * This program is free software: you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation, either version 3 of the License, or
- * (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program. If not, see <http://www.gnu.org/licenses/>.
- */
-/** @file alsabg.c
- * @brief Background-thread interface to ALSA
- *
- * This wraps ALSA with an interface which calls back to the client from a
- * thread. It's not intended for completely general use, just what DisOrder
- * needs.
- *
- * Only builds on Linux systems.
- */
-
-#include "common.h"
-
-#if HAVE_ALSA_ASOUNDLIB_H
-#include <alsa/asoundlib.h>
-#include <pthread.h>
-
-#include "alsabg.h"
-#include "log.h"
-
-/** @brief Output handle */
-static snd_pcm_t *pcm;
-
-/** @brief Called to get audio data */
-static alsa_bg_supply *supplyfn;
-
-static pthread_t alsa_bg_collect_tid, alsa_bg_play_tid;
-
-/** @brief Set to shut down the background threads */
-static int alsa_bg_shutdown = 0;
-
-/** @brief Number of channels (samples per frame) */
-#define CHANNELS 2
-
-/** @brief Number of bytes per samples */
-#define BYTES_PER_SAMPLE 2
-
-/** @brief Number of bytes per frame */
-#define BYTES_PER_FRAME (CHANNELS * BYTES_PER_SAMPLE)
-
-/** @brief Buffer size in bytes */
-#define BUFFER_BYTES 65536
-
-/** @brief Buffer size in frames */
-#define BUFFER_FRAMES (BUFFER_BYTES / BYTES_PER_FRAME)
-
-/** @brief Buffer size in samples */
-#define BUFFER_SAMPLES (BUFFER_BYTES / BYTES_PER_SAMPLE)
-
-/** @brief Audio buffer */
-static uint8_t alsa_bg_buffer[BUFFER_BYTES];
-
-/** @brief First playable byte in audio buffer */
-static unsigned alsa_bg_start;
-
-/** @brief Number of playable bytes in audio buffer */
-static unsigned alsa_bg_count;
-
-/** @brief Current enable status */
-static int alsa_bg_enabled;
-
-/** @brief Lock protecting audio buffer pointers */
-static pthread_mutex_t alsa_bg_lock = PTHREAD_MUTEX_INITIALIZER;
-
-/** @brief Signaled when buffer contents changes */
-static pthread_cond_t alsa_bg_cond = PTHREAD_COND_INITIALIZER;
-
-/** @brief Call a pthread_ function and fatal() on exit */
-#define ep(x) do { \
- int prc; \
- \
- if((prc = (x))) \
- fatal(prc, "%s", #x); \
-} while(0)
-
-/** @brief Data collection thread
- *
- * This thread collects audio data to play and stores it in the ring
- * buffer.
- */
-static void *alsa_bg_collect(void attribute((unused)) *arg) {
- unsigned avail_start, avail_count;
- int count;
-
- ep(pthread_mutex_lock(&alsa_bg_lock));
- for(;;) {
- /* If we're shutting down, quit straight away */
- if(alsa_bg_shutdown)
- break;
- /* While we're disabled or the buffer is full, just wait */
- if(!alsa_bg_enabled || alsa_bg_count == BUFFER_BYTES) {
- ep(pthread_cond_wait(&alsa_bg_cond, &alsa_bg_lock));
- continue;
- }
- /* Figure out where and how big the gap we can write into is */
- avail_start = alsa_bg_start + alsa_bg_count;
- if(avail_start < BUFFER_BYTES)
- avail_count = BUFFER_BYTES - avail_start;
- else {
- avail_start %= BUFFER_BYTES;
- avail_count = alsa_bg_start - avail_start;
- }
- assert(avail_start < BUFFER_BYTES);
- assert(avail_count <= BUFFER_BYTES);
- assert(avail_count + alsa_bg_count <= BUFFER_BYTES);
- ep(pthread_mutex_unlock(&alsa_bg_lock));
- count = supplyfn(alsa_bg_buffer + avail_start,
- avail_count / BYTES_PER_SAMPLE);
- ep(pthread_mutex_lock(&alsa_bg_lock));
- alsa_bg_count += count * BYTES_PER_SAMPLE;
- assert(alsa_bg_start < BUFFER_BYTES);
- assert(alsa_bg_count <= BUFFER_BYTES);
- ep(pthread_cond_signal(&alsa_bg_cond));
- }
- ep(pthread_mutex_unlock(&alsa_bg_lock));
- return 0;
-}
-
-/** @brief Playback thread
- *
- * This thread reads audio data out of the ring buffer and plays it back
- */
-static void *alsa_bg_play(void attribute((unused)) *arg) {
- int prepared = 1, err;
- int start, nbytes, nframes, rframes;
-
- ep(pthread_mutex_lock(&alsa_bg_lock));
- for(;;) {
- /* If we're shutting down, quit straight away */
- if(alsa_bg_shutdown)
- break;
- /* Wait for some data to be available. (If we are marked disabled
- * we keep on playing what we've got.) */
- if(alsa_bg_count == 0) {
- if(prepared) {
- if((err = snd_pcm_drain(pcm)))
- fatal(0, "snd_pcm_drain: %d", err);
- prepared = 0;
- }
- ep(pthread_cond_wait(&alsa_bg_cond, &alsa_bg_lock));
- continue;
- }
- /* Calculate how much we can play */
- start = alsa_bg_start;
- if(start + alsa_bg_count <= BUFFER_BYTES)
- nbytes = alsa_bg_count;
- else
- nbytes = BUFFER_BYTES - start;
- /* Limit how much of the buffer we play. The effect is that we return from
- * _writei earlier, and therefore free up more buffer space to read fresh
- * data into. /2 works fine, /4 is just conservative. /1 (i.e. abolishing
- * the heuristic) produces noticably noisy output. */
- if(nbytes > BUFFER_BYTES / 4)
- nbytes = BUFFER_BYTES / 4;
- assert((unsigned)nbytes <= alsa_bg_count);
- nframes = nbytes / BYTES_PER_FRAME;
- ep(pthread_mutex_unlock(&alsa_bg_lock));
- /* Make sure the PCM is prepared */
- if(!prepared) {
- if((err = snd_pcm_prepare(pcm)))
- fatal(0, "snd_pcm_prepare: %d", err);
- prepared = 1;
- }
- /* Play what we can */
- rframes = snd_pcm_writei(pcm, alsa_bg_buffer + start, nframes);
- ep(pthread_mutex_lock(&alsa_bg_lock));
- if(rframes < 0) {
- switch(rframes) {
- case -EPIPE:
- error(0, "underrun detected");
- if((err = snd_pcm_prepare(pcm)))
- fatal(0, "snd_pcm_prepare: %d", err);
- break;
- default:
- fatal(0, "snd_pcm_writei: %d", rframes);
- }
- } else {
- const int rbytes = rframes * BYTES_PER_FRAME;
- /*fprintf(stderr, "%5d -> %5d\n", nbytes, rbytes);*/
- /* Update the buffer pointers */
- alsa_bg_count -= rbytes;
- alsa_bg_start += rbytes;
- if(alsa_bg_start >= BUFFER_BYTES)
- alsa_bg_start -= BUFFER_BYTES;
- assert(alsa_bg_start < BUFFER_BYTES);
- assert(alsa_bg_count <= BUFFER_BYTES);
- /* Let the collector know we've opened up some space */
- ep(pthread_cond_signal(&alsa_bg_cond));
- }
- }
- ep(pthread_mutex_unlock(&alsa_bg_lock));
- return 0;
-}
-
-/** @brief Enable ALSA play */
-void alsa_bg_enable(void) {
- ep(pthread_mutex_lock(&alsa_bg_lock));
- alsa_bg_enabled = 1;
- ep(pthread_cond_broadcast(&alsa_bg_cond));
- ep(pthread_mutex_unlock(&alsa_bg_lock));
-}
-
-/** @brief Disable ALSA play */
-void alsa_bg_disable(void) {
- ep(pthread_mutex_lock(&alsa_bg_lock));
- alsa_bg_enabled = 0;
- ep(pthread_cond_broadcast(&alsa_bg_cond));
- ep(pthread_mutex_unlock(&alsa_bg_lock));
-}
-
-/** @brief Initialize background ALSA playback
- * @param device Target device or NULL to use default
- * @param supply Function to call to get audio data to play
- *
- * Playback is not initially enabled; see alsa_bg_enable(). When playback is
- * enabled, @p supply will be called in a background thread to request audio
- * data. It should return in a timely manner, but playback happens from a
- * further thread and delays in @p supply will not delay transfer of data to
- * the sound device (provided it doesn't actually run out).
- */
-void alsa_bg_init(const char *device,
- alsa_bg_supply *supply) {
- snd_pcm_hw_params_t *hwparams;
- /* Only support one format for now */
- const int sample_format = SND_PCM_FORMAT_S16_BE;
- unsigned rate = 44100;
- int err;
-
- if((err = snd_pcm_open(&pcm,
- device ? device : "default",
- SND_PCM_STREAM_PLAYBACK,
- 0)))
- fatal(0, "error from snd_pcm_open: %d", err);
- /* Set up 'hardware' parameters */
- snd_pcm_hw_params_alloca(&hwparams);
- if((err = snd_pcm_hw_params_any(pcm, hwparams)) < 0)
- fatal(0, "error from snd_pcm_hw_params_any: %d", err);
- if((err = snd_pcm_hw_params_set_access(pcm, hwparams,
- SND_PCM_ACCESS_RW_INTERLEAVED)) < 0)
- fatal(0, "error from snd_pcm_hw_params_set_access: %d", err);
- if((err = snd_pcm_hw_params_set_format(pcm, hwparams,
- sample_format)) < 0)
-
- fatal(0, "error from snd_pcm_hw_params_set_format (%d): %d",
- sample_format, err);
- if((err = snd_pcm_hw_params_set_rate_near(pcm, hwparams, &rate, 0)) < 0)
- fatal(0, "error from snd_pcm_hw_params_set_rate (%d): %d",
- rate, err);
- if((err = snd_pcm_hw_params_set_channels(pcm, hwparams,
- CHANNELS)) < 0)
- fatal(0, "error from snd_pcm_hw_params_set_channels (%d): %d",
- CHANNELS, err);
- if((err = snd_pcm_hw_params(pcm, hwparams)) < 0)
- fatal(0, "error calling snd_pcm_hw_params: %d", err);
-
- /* Record the audio supply function */
- supplyfn = supply;
-
- /* Create the audio output thread */
- alsa_bg_shutdown = 0;
- alsa_bg_enabled = 0;
- ep(pthread_create(&alsa_bg_collect_tid, 0, alsa_bg_collect, 0));
- ep(pthread_create(&alsa_bg_play_tid, 0, alsa_bg_play, 0));
-}
-
-/** @brief Deinitialize background ALSA playback
- *
- * The opposite of alsa_bg_init().
- */
-void alsa_bg_close(void) {
- void *r;
-
- /* Notify background threads that we're shutting down */
- ep(pthread_mutex_lock(&alsa_bg_lock));
- alsa_bg_enabled = 0;
- alsa_bg_shutdown = 1;
- ep(pthread_cond_signal(&alsa_bg_cond));
- ep(pthread_mutex_unlock(&alsa_bg_lock));
- /* Join background threads when they're done */
- ep(pthread_join(alsa_bg_collect_tid, &r));
- ep(pthread_join(alsa_bg_play_tid, &r));
- /* Close audio device */
- snd_pcm_close(pcm);
- pcm = 0;
-}
-
-#endif
-
-/*
-Local Variables:
-c-basic-offset:2
-comment-column:40
-fill-column:79
-indent-tabs-mode:nil
-End:
-*/
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