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        #include <stdio.h>
        #include <stdlib.h>
        #include <errno.h>
        #include <poll.h>
        #include <alsa/asoundlib.h>

/* you allocate these in heap */
int             restarting;
int             fragments = 2;
int             channels = 1;
int             buffer_size = 512;
int             sample_rate = 48000;
int             frame_size = 1024;
int             bits = 16;

char           *snd_device_in  = "plughw:0,0";
char           *snd_device_out = "plughw:0,0";
snd_pcm_t      *playback_handle;
snd_pcm_t      *capture_handle;

int err;

int configure_alsa_audio(snd_pcm_t *device, int channels)
{
    snd_pcm_hw_params_t *hw_params;
    int                 err;
    int                 tmp;

    snd_pcm_uframes_t   frames;

    /* allocate memory for hardware parameter structure */ 
    if ((err = snd_pcm_hw_params_malloc(&hw_params)) < 0) {
        fprintf (stderr, "cannot allocate parameter structure (%s)\n",
                 snd_strerror(err));
        return 1;
    }
    /* fill structure from current audio parameters */
    if ((err = snd_pcm_hw_params_any(device, hw_params)) < 0) {
        fprintf (stderr, "cannot initialize parameter structure (%s)\n",
                 snd_strerror(err));
        return 1;
    }

    /* set access type, sample rate, sample format, channels */
    if ((err = snd_pcm_hw_params_set_access(device, hw_params, SND_PCM_ACCESS_RW_INTERLEAVED)) < 0) {
        fprintf (stderr, "cannot set access type: %s\n",
                 snd_strerror(err));
        return 1;
    }
    // bits = 16
    if ((err = snd_pcm_hw_params_set_format(device, hw_params, SND_PCM_FORMAT_S16_LE)) < 0) {
        fprintf (stderr, "cannot set sample format: %s\n",
                 snd_strerror(err));
        return 1;
    }
    tmp = sample_rate;    
    if ((err = snd_pcm_hw_params_set_rate_near(device, hw_params, &tmp, 0)) < 0) {
        fprintf (stderr, "cannot set sample rate: %s\n",
                 snd_strerror(err));
        return 1;
    }
    if (tmp != sample_rate) {
        fprintf(stderr, "Could not set requested sample rate, asked for %d got %d\n", sample_rate, tmp);
        sample_rate = tmp;
    }
    if ((err = snd_pcm_hw_params_set_channels(device, hw_params, channels)) < 0) {
        fprintf (stderr, "cannot set channel count: %s\n",
                 snd_strerror(err));
        return 1;
    }

    if ((err = snd_pcm_hw_params_set_periods_near(device, hw_params, &fragments, 0)) < 0) {
        fprintf(stderr, "Error setting # fragments to %d: %s\n", fragments,
                snd_strerror(err));
        return 1;
    }

    frame_size = channels * (bits / 8);
    frames = buffer_size / frame_size * fragments;
    if ((err = snd_pcm_hw_params_set_buffer_size_near(device, hw_params, &frames)) < 0) {
        fprintf(stderr, "Error setting buffer_size %d frames: %s\n", frames,
                snd_strerror(err));
        return 1;
    }
    if (buffer_size != frames * frame_size / fragments) {
        fprintf(stderr, "Could not set requested buffer size, asked for %d got %d\n", buffer_size, frames * frame_size / fragments);
        buffer_size = frames * frame_size / fragments;
    }
    if ((err = snd_pcm_hw_params(device, hw_params)) < 0) {
        fprintf(stderr, "Error setting HW params: %s\n",
                snd_strerror(err));
        return 1;
    }
    return 0;
}
              
main (void)
{
        
int i,frames, inframes, outframes, frame_size;

if ((err = snd_pcm_open(&playback_handle, snd_device_out, SND_PCM_STREAM_PLAYBACK, 0)) < 0) {
    fprintf(stderr, "cannot open output audio device %s: %s\n", snd_device_in, snd_strerror(err));
    exit(1);
}

if ((err = snd_pcm_open(&capture_handle, snd_device_in, SND_PCM_STREAM_CAPTURE, 0)) < 0) {
    fprintf(stderr, "cannot open input audio device %s: %s\n", snd_device_out, snd_strerror(err));
    exit(1);
}

configure_alsa_audio(snd_device_in,  channels);
configure_alsa_audio(snd_device_out, channels);

restarting = 1;

while (1) {
    frame_size = channels * (bits / 8);
    frames = buffer_size / frame_size;

    if (restarting) {
        restarting = 0;
        /* drop any output we might got and stop */
        snd_pcm_drop(capture_handle);
        snd_pcm_drop(playback_handle);
        /* prepare for use */
        snd_pcm_prepare(capture_handle);
        snd_pcm_prepare(playback_handle);

    /* fill the whole output buffer */
    for (i = 0; i < fragments; i += 1)
    snd_pcm_writei(playback_handle, rdbuf, frames);
    }

    while ((inframes = snd_pcm_readi(capture_handle, rdbuf, frames)) < 0) {
        if (inframes == -EAGAIN)
            continue;
    // by the way, writing to terminal emulator is costly if you use
    // bad emulators like gnome-terminal, so don't do this.
        fprintf(stderr, "Input buffer overrun\n");
        restarting = 1;
        snd_pcm_prepare(capture_handle);
    }
    if (inframes != frames)
        fprintf(stderr, "Short read from capture device: %d, expecting %d\n", inframes, frames);

    /* now processes the frames */
    do_something(rdbuf, inframes);

    while ((outframes = snd_pcm_writei(playback_handle, rdbuf, inframes)) < 0) {
        if (outframes == -EAGAIN)
            continue;
        fprintf(stderr, "Output buffer underrun\n");
        restarting = 1;
        snd_pcm_prepare(playback_handle);
    }
    if (outframes != inframes)
        fprintf(stderr, "Short write to playback device: %d, expecting %d\n", outframes, frames);


        
                snd_pcm_close(snd_device_out);
                snd_pcm_close(snd_device_in);
                exit (0);
}