+
+#if API_ALSA
+/** @brief PCM handle */
+static snd_pcm_t *pcm;
+
+/** @brief True when @ref pcm is up and running */
+static int alsa_prepared = 1;
+
+/** @brief Initialize @ref pcm */
+static void setup_alsa(void) {
+ snd_pcm_hw_params_t *hwparams;
+ snd_pcm_sw_params_t *swparams;
+ /* Only support one format for now */
+ const int sample_format = SND_PCM_FORMAT_S16_BE;
+ unsigned rate = 44100;
+ const int channels = 2;
+ const int samplesize = channels * sizeof(uint16_t);
+ snd_pcm_uframes_t pcm_bufsize = MAXSAMPLES * samplesize * 3;
+ /* If we can write more than this many samples we'll get a wakeup */
+ const int avail_min = 256;
+ int err;
+
+ /* Open ALSA */
+ if((err = snd_pcm_open(&pcm,
+ device ? device : "default",
+ SND_PCM_STREAM_PLAYBACK,
+ SND_PCM_NONBLOCK)))
+ 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_set_buffer_size_near(pcm, hwparams,
+ &pcm_bufsize)) < 0)
+ fatal(0, "error from snd_pcm_hw_params_set_buffer_size (%d): %d",
+ MAXSAMPLES * samplesize * 3, err);
+ if((err = snd_pcm_hw_params(pcm, hwparams)) < 0)
+ fatal(0, "error calling snd_pcm_hw_params: %d", err);
+ /* Set up 'software' parameters */
+ snd_pcm_sw_params_alloca(&swparams);
+ if((err = snd_pcm_sw_params_current(pcm, swparams)) < 0)
+ fatal(0, "error calling snd_pcm_sw_params_current: %d", err);
+ if((err = snd_pcm_sw_params_set_avail_min(pcm, swparams, avail_min)) < 0)
+ fatal(0, "error calling snd_pcm_sw_params_set_avail_min %d: %d",
+ avail_min, err);
+ if((err = snd_pcm_sw_params(pcm, swparams)) < 0)
+ fatal(0, "error calling snd_pcm_sw_params: %d", err);
+}
+
+/** @brief Wait until ALSA wants some audio */
+static void wait_alsa(void) {
+ struct pollfd fds[64];
+ int nfds, err;
+ unsigned short events;
+
+ for(;;) {
+ do {
+ if((nfds = snd_pcm_poll_descriptors(pcm,
+ fds, sizeof fds / sizeof *fds)) < 0)
+ fatal(0, "error calling snd_pcm_poll_descriptors: %d", nfds);
+ } while(poll(fds, nfds, -1) < 0 && errno == EINTR);
+ if((err = snd_pcm_poll_descriptors_revents(pcm, fds, nfds, &events)))
+ fatal(0, "error calling snd_pcm_poll_descriptors_revents: %d", err);
+ if(events & POLLOUT)
+ return;
+ }
+}
+
+/** @brief Play some sound via ALSA
+ * @param s Pointer to sample data
+ * @param n Number of samples
+ * @return 0 on success, -1 on non-fatal error
+ */
+static int alsa_writei(const void *s, size_t n) {
+ /* Do the write */
+ const snd_pcm_sframes_t frames_written = snd_pcm_writei(pcm, s, n / 2);
+ if(frames_written < 0) {
+ /* Something went wrong */
+ switch(frames_written) {
+ case -EAGAIN:
+ return 0;
+ case -EPIPE:
+ error(0, "error calling snd_pcm_writei: %ld",
+ (long)frames_written);
+ return -1;
+ default:
+ fatal(0, "error calling snd_pcm_writei: %ld",
+ (long)frames_written);
+ }
+ } else {
+ /* Success */
+ next_timestamp += frames_written * 2;
+ return 0;
+ }
+}
+
+/** @brief Play the relevant part of a packet
+ * @param p Packet to play
+ * @return 0 on success, -1 on non-fatal error
+ */
+static int alsa_play(const struct packet *p) {
+ return alsa_writei(p->samples_raw + next_timestamp - p->timestamp,
+ (p->timestamp + p->nsamples) - next_timestamp);
+}
+
+/** @brief Play some silence
+ * @param p Next packet or NULL
+ * @return 0 on success, -1 on non-fatal error
+ */
+static int alsa_infill(const struct packet *p) {
+ static const uint16_t zeros[INFILL_SAMPLES];
+ size_t samples_available = INFILL_SAMPLES;
+
+ if(p && samples_available > p->timestamp - next_timestamp)
+ samples_available = p->timestamp - next_timestamp;
+ return alsa_writei(zeros, samples_available);
+}
+
+/** @brief Reset ALSA state after we lost synchronization */
+static void alsa_reset(int hard_reset) {
+ int err;
+
+ if((err = snd_pcm_nonblock(pcm, 0)))
+ fatal(0, "error calling snd_pcm_nonblock: %d", err);
+ if(hard_reset) {
+ if((err = snd_pcm_drop(pcm)))
+ fatal(0, "error calling snd_pcm_drop: %d", err);
+ } else
+ if((err = snd_pcm_drain(pcm)))
+ fatal(0, "error calling snd_pcm_drain: %d", err);
+ if((err = snd_pcm_nonblock(pcm, 1)))
+ fatal(0, "error calling snd_pcm_nonblock: %d", err);
+ alsa_prepared = 0;
+}
+#endif
+