Упражнение 7. Аудио контролер

Цел на упражнението

Запознаване със средствата за работа със звук.

Alsa Advanced Linux Sound Architecture Състои се от набор от драйвери, API функции и инструменти.

libasound2-dev

#include <stdio.h>
#include <stdlib.h>
#include <alsa/asoundlib.h>
	      
int main (int argc, char *argv[])
{
  /* Handle for the PCM device */ 
  snd_pcm_t *pcm_handle;          

  /* Playback stream */
  snd_pcm_stream_t stream = SND_PCM_STREAM_PLAYBACK;

  /* This structure contains information about    */
  /* the hardware and can be used to specify the  */      
  /* configuration to be used for the PCM stream. */ 
  snd_pcm_hw_params_t *hwparams;


   /* Name of the PCM device, like plughw:0,0          */
    /* The first number is the number of the soundcard, */
    /* the second number is the number of the device.   */
    char *pcm_name;
  
  /* Init pcm_name. Of course, later you */
    /* will make this configurable ;-)     */
   pcm_name = strdup("default");
  
    /* Allocate the snd_pcm_hw_params_t structure on the stack. */
    snd_pcm_hw_params_alloca(&hwparams);
  
    /* Open PCM. The last parameter of this function is the mode. */
    /* If this is set to 0, the standard mode is used. Possible   */
    /* other values are SND_PCM_NONBLOCK and SND_PCM_ASYNC.       */ 
    /* If SND_PCM_NONBLOCK is used, read / write access to the    */
    /* PCM device will return immediately. If SND_PCM_ASYNC is    */
    /* specified, SIGIO will be emitted whenever a period has     */
    /* been completely processed by the soundcard.                */
    if (snd_pcm_open(&pcm_handle, pcm_name, stream, 0) < 0) {
      fprintf(stderr, "Error opening PCM device %s\n", pcm_name);
      return(-1);
    }
    
    
    /* Init hwparams with full configuration space */
    if (snd_pcm_hw_params_any(pcm_handle, hwparams) < 0) {
      fprintf(stderr, "Can not configure this PCM device.\n");
      return(-1);
    }
    
    
    
    
    
    unsigned int rate = 44100; /* Sample rate */
    unsigned int exact_rate;   /* Sample rate returned by */
                      /* snd_pcm_hw_params_set_rate_near */ 
    int dir;          /* exact_rate == rate --> dir = 0 */
                      /* exact_rate < rate  --> dir = -1 */
                      /* exact_rate > rate  --> dir = 1 */
    int periods = 2;       /* Number of periods */
    snd_pcm_uframes_t periodsize = 512; /* Periodsize (bytes) */
    
     /* Set sample format */
    if (snd_pcm_hw_params_set_format(pcm_handle, hwparams, SND_PCM_FORMAT_S16_LE) < 0) {
      fprintf(stderr, "Error setting format.\n");
      return(-1);
    }
    
    /* Set sample rate. If the exact rate is not supported */
    /* by the hardware, use nearest possible rate.         */ 
    exact_rate = rate;
    
    if (snd_pcm_hw_params_set_rate_near(pcm_handle, hwparams, &exact_rate, 0) < 0) {
      fprintf(stderr, "Error setting rate.\n");
      return(-1);
    }
    
    if (rate != exact_rate) {
      fprintf(stderr, "The rate %d Hz is not supported by your hardware.\n ==> Using %d Hz instead.\n", rate, exact_rate);
    }
    
     /* Set number of channels */
    if (snd_pcm_hw_params_set_channels(pcm_handle, hwparams, 2) < 0) {
      fprintf(stderr, "Error setting channels.\n");
      return(-1);
    }

    /* Set number of periods. Periods used to be called fragments. 
    if (snd_pcm_hw_params_set_periods(pcm_handle, hwparams, periods, 0) < 0) {
      fprintf(stderr, "Error setting periods.\n");
      return(-1);
    }*/ 
    
    
    /* Set buffer size (in frames). The resulting latency is given by */
    /* latency = periodsize * periods / (rate * bytes_per_frame)     */
    if (snd_pcm_hw_params_set_buffer_size(pcm_handle, hwparams, (periodsize * periods)>>2) < 0) {
      fprintf(stderr, "Error setting buffersize.\n");
      return(-1);
    }
    
     /* Apply HW parameter settings to */
    /* PCM device and prepare device  */
    if (snd_pcm_hw_params(pcm_handle, hwparams) < 0) {
      fprintf(stderr, "Error setting HW params.\n");
      return(-1);
    }
    
    
    /* Write num_frames frames from buffer data to    */ 
    /* the PCM device pointed to by pcm_handle.       */
    /* Returns the number of frames actually written. */
    //  snd_pcm_sframes_t snd_pcm_writei(pcm_handle, data, num_frames);
    
    unsigned char *data;
    int pcmreturn, l1, l2;
    short s1, s2, s3, s4;
    int frames;
  //  int num_frames= 100;

    data = (unsigned char *)malloc(periodsize);
    frames = periodsize >> 3;
    for(l1 = 0; l1 < 10000; l1++) {
      
      for(l2 = 0; l2 < frames; l2++) {
        
        s1 = (l2 % 64)  * 100 - 5000;  
        s2 = (l2 % 128) * 100 - 5000;
        s3 = (l2 % 192) * 100 - 5000;  
        s4 = (l2 % 256) * 100 - 5000;    
        
        data[8*l2] = (unsigned char)s1;
        data[8*l2+1] = s1 >> 8;
        data[8*l2+2] = (unsigned char)s2;
        data[8*l2+3] = s2 >> 8;
        
        data[8*l2+4] = (unsigned char)s4;
        data[8*l2+5] = s3 >> 8;
        data[8*l2+6] = (unsigned char)s3;
        data[8*l2+7] = s4 >> 8;
      
      }
      while ((pcmreturn = snd_pcm_writei(pcm_handle, data, frames)) < 0) {
        snd_pcm_prepare(pcm_handle);
        fprintf(stderr, "<<<<<<<<<<<<<<< Buffer Underrun >>>>>>>>>>>>>>>\n");
      }
    }
    /*
    
     unsigned char *data;
    int pcmreturn, l1, l2;
    short s1, s2;
    int frames;

    data = (unsigned char *)malloc(periodsize);
    frames = periodsize >> 2;
    for(l1 = 0; l1 < 10000; l1++) {
      for(l2 = 0; l2 < frames; l2++) {
        s1 = (l2 % 128) * 100 - 5000;  
        s2 = (l2 % 256) * 100 - 5000;  
        data[4*l2] = (unsigned char)s1;
        data[4*l2+1] = s1 >> 8;
        data[4*l2+2] = (unsigned char)s2;
        data[4*l2+3] = s2 >> 8;
      }
      while ((pcmreturn = snd_pcm_writei(pcm_handle, data, frames)) < 0) {
        snd_pcm_prepare(pcm_handle);
        fprintf(stderr, "<<<<<<<<<<<<<<< Buffer Underrun >>>>>>>>>>>>>>>\n");
      }
    }*/
  return 0;
}

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