On some systems the ALSA output buffer is pretty big, and if the audio samples are not being passed into the buffer quickly enough, it becomes starved for data, resulting in an error called underrun. Previously, when it happenned, GAPK used to stop processing with the following message (where X is a random number): [+] PQ: Adding ALSA output (dev='default', blk_len=320) [!] pq_execute(): abort, item returned -1 [+] Processed X frames According to the ALSA documentation, the pcm_handle changes its state when the problem happens, and should be recovered using the snd_pcm_prepare() call. This change actually does that. --- src/pq_alsa.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/src/pq_alsa.c b/src/pq_alsa.c index 9cee426..a3435dd 100644 --- a/src/pq_alsa.c +++ b/src/pq_alsa.c @@ -57,7 +57,15 @@ pq_cb_alsa_output(void *_state, uint8_t *out, const uint8_t *in, unsigned int in struct pq_state_alsa *state = _state; unsigned int num_samples = in_len/2; int rv; + rv = snd_pcm_writei(state->pcm_handle, in, num_samples); + if (rv == -EPIPE) { + /* Recover from buffer underrun */ + snd_pcm_prepare(state->pcm_handle); + /* Send a new sample again */ + rv = snd_pcm_writei(state->pcm_handle, in, num_samples); + } + return rv == num_samples ? 0 : -1; } -- 2.14.1 From: Vadim Yanitskiy &lt;axilirator(a)gmail.com&gt; Date: Sat, 2 Sep 2017 18:02:45 +0700 Subject: [PATCH 2/2] pq_alsa.c: print error message if device init fails To: openbsc(a)lists.osmocom.org Cc: 246tnt(a)gmail.com, laforge(a)gnumonks.org, axilirator(a)gmail.com --- src/pq_alsa.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-) diff --git a/src/pq_alsa.c b/src/pq_alsa.c index a3435dd..cad76ca 100644 --- a/src/pq_alsa.c +++ b/src/pq_alsa.c @@ -85,13 +85,16 @@ pq_queue_alsa_op(struct pq *pq, const char *alsa_dev, unsigned int blk_len, int int rc = -1; state = calloc(1, sizeof(struct pq_state_alsa)); - if (!state) - return -ENOMEM; + if (!state) { + rc = -ENOMEM; + goto out_print; + } rc = snd_pcm_open(&state->pcm_handle, alsa_dev, in_out_n ? SND_PCM_STREAM_CAPTURE : SND_PCM_STREAM_PLAYBACK, 0); if (rc < 0) - return rc; + goto out_print; + state->blk_len = blk_len; rc = snd_pcm_hw_params_malloc(&hw_params); @@ -143,6 +146,9 @@ out_free_par: out_close: snd_pcm_close(state->pcm_handle); free(state); +out_print: + fprintf(stderr, "[!] Couldn't init ALSA device '%s': %s\n", + alsa_dev, snd_strerror(rc)); return rc; } -- 2.14.1