Add Alsa polling examples (simple + complex usecase)
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laurensmiers
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d31864be6e
1 changed files with 326 additions and 2 deletions
328
alsa_info.md
328
alsa_info.md
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@ -658,10 +658,79 @@ Oh you naive fool....
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#### Polling
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```c
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#include <stdio.h>
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#include <alsa/asoundlib.h>
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#define AUDIO_SAMPLERATE 16000
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#define AUDIO_NR_OF_SAMPLES 128u
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#define AUDIO_BYTES_PER_SAMPLE 2u
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#define AUDIO_OUTPUT_NR_CHANNELS 2u
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#define SAMPLE_BUFFER_SIZE (AUDIO_NR_OF_SAMPLES * AUDIO_OUTPUT_NR_CHANNELS * AUDIO_BYTES_PER_SAMPLE)
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#define PERIOD_SIZE_US 8000u
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int main(int argc, char **argv)
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{
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//TODO
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int error = 0;
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struct pollfd *ufds = NULL;
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snd_pcm_t *pcm_handle = NULL;
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int poll_fd_count = 0;
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char my_samples[SAMPLE_BUFFER_SIZE] = { 0 };
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int revents = 0;
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snd_pcm_open(&pcm_handle, "default:CARD=MyAwesomeAudioCard", SND_PCM_STREAM_PLAYBACK, 0);
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// default setup stuff here....
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// Set start value
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if (err < snd_pcm_sw_params_set_avail_min(handle, swparams, period_size)) {
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printf("Unable to set avail min for playback: %s\n", snd_strerror(err));
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return err;
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}
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// Enable poll event
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err = snd_pcm_sw_params_set_period_event(handle, swparams, 1);
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if (err < 0) {
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printf("Unable to set period event: %s\n", snd_strerror(err));
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return err;
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}
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// Set SW params
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if ((err = snd_pcm_sw_params(handle, swparams)) < 0) {
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printf("ERROR: Can't set software parameters. %s\n", snd_strerror(err));
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return err;
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}
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// Get number of file descriptors (can be more than 1, depends on driver)
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poll_fd_count = snd_pcm_poll_descriptors_count(pcm_handle);
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// Get the actual file descriptors
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ufds = malloc(sizeof(*ufds) * poll_fd_count);
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snd_pcm_poll_descriptors(pcm_handle, ufds, poll_fd_count);
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// start device
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snd_pcm_start(pcm_handle);
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while (1) {
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poll(ufds, poll_fd_count, -1);
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snd_pcm_poll_descriptors_revents(pcm_handle, ufds, poll_fd_count, &revents);
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if (revents & POLLERR) {
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// All hope is lost...
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} else if (revents & POLLOUT) {
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error = snd_pcm_writei(pcm_handle, my_samples, AUDIO_NR_OF_SAMPLES);
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if (error < 0) {
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// xrun recovery
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}
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}
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// Throttle our thread...
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usleep(PERIOD_SIZE_US / 2)
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}
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return 0;
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}
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```
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@ -707,10 +776,265 @@ Extrapolate the blocking usecase
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#### Polling
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```c
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#include <stdio.h>
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#include <stdlib.h>
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#include <unistd.h>
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#include <time.h>
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#include <pthread.h>
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#include <alsa/asoundlib.h>
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#include <alloca.h>
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#define AUDIO_NR_OF_SAMPLES 128u
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#define AUDIO_BYTES_PER_SAMPLE 2u
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#define AUDIO_NR_OF_CHANNELS 2u
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#define SAMPLE_BUFFER_SIZE (AUDIO_NR_OF_SAMPLES * AUDIO_NR_OF_CHANNELS * AUDIO_BYTES_PER_SAMPLE)
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static char *device_names[] = {
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"sysdefault:CARD=AudioBoard00",
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"sysdefault:CARD=AudioBoard01",
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"sysdefault:CARD=AudioBoard02",
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"sysdefault:CARD=AudioBoard03",
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"sysdefault:CARD=AudioBoard04",
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"sysdefault:CARD=AudioBoard05",
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"sysdefault:CARD=AudioBoard06",
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"sysdefault:CARD=AudioBoard07",
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};
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#define NR_OF_DEVICES (sizeof(device_names)/sizeof(*device_names))
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static void *read_thread_func(void *cookie)
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{
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int error = 0;
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struct pollfd *ufds = NULL;
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snd_pcm_t *pcm_handles[NR_OF_DEVICES];
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int poll_fd_count[NR_OF_DEVICES] = { 0 };
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int total_poll_fd_count = 0;
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int poll_fd_count_offset[NR_OF_DEVICES] = { 0 };
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for (int i = 0; i< NR_OF_DEVICES; ++i) {
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if (snd_pcm_open(&pcm_handles[i], device_names[i], SND_PCM_STREAM_CAPTURE, 0) < 0) {
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printf("Failed to open device '%s'\n", device_names[i]);
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goto _free_resources;
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}
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// setup hw/sw params of alsa device...
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poll_fd_count[i] = snd_pcm_poll_descriptors_count(pcm_handles[i]);
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if (poll_fd_count[i] <= 0) {
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printf("Invalid poll descriptors count for device '%s'\n", device_names[i]);
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goto _free_resources;
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}
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total_poll_fd_count += poll_fd_count[i];
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}
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ufds = malloc(sizeof(*ufds) * total_poll_fd_count);
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if (ufds == NULL) {
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printf("Not enough memory\n");
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goto _free_resources;
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}
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memset(ufds, 0, sizeof(*ufds) * total_poll_fd_count);
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for (int i = 1; i < NR_OF_DEVICES; ++i) {
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for (int j = 0; j < i; j++) {
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poll_fd_count_offset[i] += poll_fd_count[j];
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}
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}
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/* Get poll file descriptors */
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for (int i = 0; i< NR_OF_DEVICES; ++i) {
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if ((error = snd_pcm_poll_descriptors(pcm_handles[i], ufds + poll_fd_count_offset[i], poll_fd_count[i])) < 0) {
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printf("Unable to obtain poll descriptors for playback: %s\n", snd_strerror(error));
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goto _free_resources;
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}
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}
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/* Start readers */
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for (int i = 0; i < NR_OF_DEVICES; i++) {
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if (snd_pcm_start(pcm_handles[i]) < 0) {
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printf("Failed to start pcm '%s'", device_names[i]);
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goto _free_resources;
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}
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}
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char black_hole[SAMPLE_BUFFER_SIZE] = {0};
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while (1) {
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unsigned short revents = 0;
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poll(ufds, total_poll_fd_count, -1);
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for (int i = 0; i < NR_OF_DEVICES; i++) {
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revents = 0;
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snd_pcm_poll_descriptors_revents(pcm_handles[i], ufds + poll_fd_count_offset[i], poll_fd_count[i], &revents);
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if (revents & POLLERR) {
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printf("ERROR:Failed to poll device %s\n", device_names[i]);
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break;
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} else if (revents & POLLIN) {
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error = snd_pcm_readi(pcm_handles[i], black_hole, AUDIO_NR_OF_SAMPLES);
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if (error < 0) {
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// xrun recovery
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}
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}
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}
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}
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printf("Reader done...\n");
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for (int i = 0; i < NR_OF_DEVICES; ++i) {
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snd_pcm_drop(pcm_handles[i]);
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snd_pcm_close(pcm_handles[i]);
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}
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_free_resources:
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// clean up your shit
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}
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static void *write_thread_func(void *cookie)
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{
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int error = 0;
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struct pollfd *ufds = NULL;
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snd_pcm_t *pcm_handles[NR_OF_DEVICES];
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int poll_fd_count[NR_OF_DEVICES] = { 0 };
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int total_poll_fd_count = 0;
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int poll_fd_count_offset[NR_OF_DEVICES] = { 0 };
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for (int i = 0; i< NR_OF_DEVICES; ++i) {
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if (snd_pcm_open(&pcm_handles[i], device_names[i], SND_PCM_STREAM_PLAYBACK, 0) < 0) {
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printf("Failed to open device '%s'\n", device_names[i]);
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goto _free_resources;
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}
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// setup hw/sw params
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poll_fd_count[i] = snd_pcm_poll_descriptors_count(pcm_handles[i]);
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if (poll_fd_count[i] <= 0) {
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printf("Invalid poll descriptors count for device '%s'\n", device_names[i]);
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goto _free_resources;
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}
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total_poll_fd_count += poll_fd_count[i];
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}
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ufds = malloc(sizeof(*ufds) * total_poll_fd_count);
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if (ufds == NULL) {
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printf("Not enough memory\n");
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goto _free_resources;
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}
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memset(ufds, 0, sizeof(*ufds) * total_poll_fd_count);
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for (int i = 1; i < NR_OF_DEVICES; ++i) {
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for (int j = 0; j < i; j++) {
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poll_fd_count_offset[i] += poll_fd_count[j];
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}
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}
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/* Get poll file descriptors */
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for (int i = 0; i< NR_OF_DEVICES; ++i) {
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if ((error = snd_pcm_poll_descriptors(pcm_handles[i], ufds + poll_fd_count_offset[i], poll_fd_count[i])) < 0) {
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printf("Unable to obtain poll descriptors for playback: %s\n", snd_strerror(error));
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goto _free_resources;
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}
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}
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/* Prefill */
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for (int i = 0; i < NR_OF_DEVICES; i++) {
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char mybuff[SAMPLE_BUFFER_SIZE * 2] = {0 };
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if (snd_pcm_writei(pcm_handles[i], mybuff, AUDIO_NR_OF_SAMPLES * 2) < 0 ) {
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printf("could not prefill\n");
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goto _free_resources;
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}
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}
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while (true) {
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unsigned short revents = 0;
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poll(ufds, total_poll_fd_count, -1);
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for (int i = 0; i < NR_OF_DEVICES; i++) {
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revents = 0;
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snd_pcm_poll_descriptors_revents(pcm_handles[i], ufds + poll_fd_count_offset[i], poll_fd_count[i], &revents);
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if (revents & POLLERR) {
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printf("ERROR:Failed to poll device '%s'\n", device_names[i]);
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if (snd_pcm_state(pcm_handles[i]) == SND_PCM_STATE_XRUN ||
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snd_pcm_state(pcm_handles[i]) == SND_PCM_STATE_SUSPENDED) {
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error = snd_pcm_state(pcm_handles[i]) == SND_PCM_STATE_XRUN ? -EPIPE : -ESTRPIPE;
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if (xrun_recovery(pcm_handles[i], error) < 0) {
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printf("Write error: %s\n", snd_strerror(error));
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exit(EXIT_FAILURE);
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}
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} else {
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LOG_ERROR("Wait for poll failed '%s'\n", device_names[i]);
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break;
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}
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/* _is_writer_done = true; */
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continue;
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} else if (revents & POLLOUT) {
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char *ptr = cbuffer_get_read_pointer(_loopback_buffers[i]);
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if (!ptr) {
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continue;
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}
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error = snd_pcm_writei(pcm_handles[i], ptr, AUDIO_NR_OF_SAMPLES);
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if (error < 0) {
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if (xrun_recovery(pcm_handles[i], error) < 0) {
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printf("Write error: %s\n", snd_strerror(error));
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exit(EXIT_FAILURE);
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}
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break;
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} else {
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/* printf("%d: Written %d samples in device %s\n", ++count, error, device_names[i]); */
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}
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cbuffer_signal_element_read(_loopback_buffers[i]);
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}
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}
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}
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printf("writer done...\n");
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for (int i = 0; i < NR_OF_DEVICES; ++i) {
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snd_pcm_drain(pcm_handles[i]);
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snd_pcm_close(pcm_handles[i]);
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}
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printf("free resources writer...\n");
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_free_resources:
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// clean up your shit
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return NULL;
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}
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int main(int argc, char **argv)
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{
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//TODO
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pthread_t write_thread;
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pthread_t read_thread;
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int error = 0;
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printf("Start playback/record with following devices:\n");
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for (int i = 0; i < NR_OF_DEVICES; ++i) {
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printf("%s\n", device_names[i]);
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}
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if (pthread_create(&read_thread, NULL, read_thread_func, NULL) < 0) {
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printf("Failed to create reader thread");
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goto _free_resources;
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}
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if (pthread_create(&write_thread, NULL, write_thread_func, NULL) < 0) {
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printf("Failed to create reader thread");
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goto _free_resources;
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}
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pthread_join(write_thread, NULL);
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pthread_join(read_thread, NULL);
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return 0;
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}
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```
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