/*                                                   
 * sound.c   
 * 先錄制幾秒種音頻數據，將其存放在內存緩沖區中，然后再進行回放，其所有的功能都是通過讀寫/dev/dsp設備文件來完成                                        
 */                                                  
#include <unistd.h>                                  
#include <fcntl.h>                                   
#include <sys/types.h>                               
#include <sys/ioctl.h>                               
#include <stdlib.h>                                  
#include <stdio.h>                                   
#include <linux/soundcard.h>                         
#define LENGTH 3    /* 存儲秒數 */                   
#define RATE 8000   /* 采樣頻率 */                   
#define SIZE 8      /* 量化位數 */                   
#define CHANNELS 1  /* 聲道數目 */                   
/* 用于保存數字音頻數據的內存緩沖區 */               
unsigned char buf[LENGTH*RATE*SIZE*CHANNELS/8];      
int main()                                           
{                                                    
  int fd;	/* 聲音設備的文件描述符 */                 
  int arg;	/* 用于ioctl調用的參數 */                
  int status;   /* 系統調用的返回值 */               
  /* 打開聲音設備 */                                 
  fd = open("/dev/dsp", O_RDWR);                     
  if (fd < 0) {                                      
    perror("open of /dev/dsp failed");               
    exit(1);                                         
  }                                                  
  /* 設置采樣時的量化位數 */                         
  arg = SIZE;                                        
  status = ioctl(fd, SOUND_PCM_WRITE_BITS, &arg);    
  if (status == -1)                                  
    perror("SOUND_PCM_WRITE_BITS ioctl failed");     
  if (arg != SIZE)                                   
    perror("unable to set sample size");             
  /* 設置采樣時的聲道數目 */                         
  arg = CHANNELS;                                    
  status = ioctl(fd, SOUND_PCM_WRITE_CHANNELS, &arg);
  if (status == -1)                                  
    perror("SOUND_PCM_WRITE_CHANNELS ioctl failed"); 
  if (arg != CHANNELS)                               
    perror("unable to set number of channels");      
  /* 設置采樣時的采樣頻率 */                         
  arg = RATE;                                        
  status = ioctl(fd, SOUND_PCM_WRITE_RATE, &arg);    
  if (status == -1)                                  
    perror("SOUND_PCM_WRITE_WRITE ioctl failed");    
  /* 循環，直到按下Control-C */                      
  while (1) {                                        
    printf("Say something:\n");                      
    status = read(fd, buf, sizeof(buf)); /* 錄音 */  
    if (status != sizeof(buf))                       
      perror("read wrong number of bytes");          
    printf("You said:\n");                           
    status = write(fd, buf, sizeof(buf)); /* 回放 */ 
    if (status != sizeof(buf))                       
      perror("wrote wrong number of bytes");         
    /* 在繼續錄音前等待回放結束 */                   
    status = ioctl(fd, SOUND_PCM_SYNC, 0);           
    if (status == -1)                                
      perror("SOUND_PCM_SYNC ioctl failed");         
  }                                                  
}