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#include <stdio.h>
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#include <stdlib.h>
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#include <errno.h>
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#include <poll.h>
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#include <alsa/asoundlib.h>
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/* you allocate these in heap */
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int restarting;
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int fragments = 2;
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int channels = 1;
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int buffer_size = 512;
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int sample_rate = 48000;
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int frame_size = 1024;
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int bits = 16;
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char *snd_device_in = "plughw:0,0";
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char *snd_device_out = "plughw:0,0";
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snd_pcm_t *playback_handle;
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snd_pcm_t *capture_handle;
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int err;
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int configure_alsa_audio(snd_pcm_t *device, int channels)
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{
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snd_pcm_hw_params_t *hw_params;
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int err;
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int tmp;
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snd_pcm_uframes_t frames;
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/* allocate memory for hardware parameter structure */
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if ((err = snd_pcm_hw_params_malloc(&hw_params)) < 0) {
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fprintf (stderr, "cannot allocate parameter structure (%s)\n",
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snd_strerror(err));
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return 1;
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}
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/* fill structure from current audio parameters */
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if ((err = snd_pcm_hw_params_any(device, hw_params)) < 0) {
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fprintf (stderr, "cannot initialize parameter structure (%s)\n",
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snd_strerror(err));
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return 1;
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}
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/* set access type, sample rate, sample format, channels */
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if ((err = snd_pcm_hw_params_set_access(device, hw_params, SND_PCM_ACCESS_RW_INTERLEAVED)) < 0) {
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fprintf (stderr, "cannot set access type: %s\n",
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snd_strerror(err));
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return 1;
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}
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// bits = 16
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if ((err = snd_pcm_hw_params_set_format(device, hw_params, SND_PCM_FORMAT_S16_LE)) < 0) {
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fprintf (stderr, "cannot set sample format: %s\n",
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snd_strerror(err));
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return 1;
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}
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tmp = sample_rate;
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if ((err = snd_pcm_hw_params_set_rate_near(device, hw_params, &tmp, 0)) < 0) {
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fprintf (stderr, "cannot set sample rate: %s\n",
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snd_strerror(err));
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return 1;
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}
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if (tmp != sample_rate) {
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fprintf(stderr, "Could not set requested sample rate, asked for %d got %d\n", sample_rate, tmp);
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sample_rate = tmp;
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}
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if ((err = snd_pcm_hw_params_set_channels(device, hw_params, channels)) < 0) {
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fprintf (stderr, "cannot set channel count: %s\n",
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snd_strerror(err));
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return 1;
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}
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if ((err = snd_pcm_hw_params_set_periods_near(device, hw_params, &fragments, 0)) < 0) {
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fprintf(stderr, "Error setting # fragments to %d: %s\n", fragments,
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snd_strerror(err));
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return 1;
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}
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frame_size = channels * (bits / 8);
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frames = buffer_size / frame_size * fragments;
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if ((err = snd_pcm_hw_params_set_buffer_size_near(device, hw_params, &frames)) < 0) {
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fprintf(stderr, "Error setting buffer_size %d frames: %s\n", frames,
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snd_strerror(err));
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return 1;
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}
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if (buffer_size != frames * frame_size / fragments) {
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fprintf(stderr, "Could not set requested buffer size, asked for %d got %d\n", buffer_size, frames * frame_size / fragments);
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buffer_size = frames * frame_size / fragments;
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}
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if ((err = snd_pcm_hw_params(device, hw_params)) < 0) {
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fprintf(stderr, "Error setting HW params: %s\n",
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snd_strerror(err));
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return 1;
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}
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return 0;
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}
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main (void)
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{
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int i,frames, inframes, outframes, frame_size;
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if ((err = snd_pcm_open(&playback_handle, snd_device_out, SND_PCM_STREAM_PLAYBACK, 0)) < 0) {
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fprintf(stderr, "cannot open output audio device %s: %s\n", snd_device_in, snd_strerror(err));
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exit(1);
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}
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if ((err = snd_pcm_open(&capture_handle, snd_device_in, SND_PCM_STREAM_CAPTURE, 0)) < 0) {
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fprintf(stderr, "cannot open input audio device %s: %s\n", snd_device_out, snd_strerror(err));
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exit(1);
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}
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configure_alsa_audio(snd_device_in, channels);
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configure_alsa_audio(snd_device_out, channels);
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restarting = 1;
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while (1) {
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frame_size = channels * (bits / 8);
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frames = buffer_size / frame_size;
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if (restarting) {
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restarting = 0;
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/* drop any output we might got and stop */
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snd_pcm_drop(capture_handle);
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snd_pcm_drop(playback_handle);
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/* prepare for use */
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snd_pcm_prepare(capture_handle);
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snd_pcm_prepare(playback_handle);
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/* fill the whole output buffer */
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for (i = 0; i < fragments; i += 1)
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snd_pcm_writei(playback_handle, rdbuf, frames);
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}
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while ((inframes = snd_pcm_readi(capture_handle, rdbuf, frames)) < 0) {
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if (inframes == -EAGAIN)
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continue;
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// by the way, writing to terminal emulator is costly if you use
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// bad emulators like gnome-terminal, so don't do this.
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fprintf(stderr, "Input buffer overrun\n");
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restarting = 1;
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snd_pcm_prepare(capture_handle);
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}
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if (inframes != frames)
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fprintf(stderr, "Short read from capture device: %d, expecting %d\n", inframes, frames);
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/* now processes the frames */
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do_something(rdbuf, inframes);
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while ((outframes = snd_pcm_writei(playback_handle, rdbuf, inframes)) < 0) {
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if (outframes == -EAGAIN)
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continue;
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fprintf(stderr, "Output buffer underrun\n");
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restarting = 1;
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snd_pcm_prepare(playback_handle);
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}
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if (outframes != inframes)
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fprintf(stderr, "Short write to playback device: %d, expecting %d\n", outframes, frames);
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snd_pcm_close(snd_device_out);
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snd_pcm_close(snd_device_in);
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exit (0);
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}
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