一个音频测试程序，录音并播放。代码如下：

#include <unistd.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/ioctl.h>
#include <stdlib.h>
#include <stdio.h>
#include <signal.h>
#include <linux/soundcard.h>
#define LENGTH 3    /* 存储秒数 */
#define RATE 8000   /* 采样频率 */
#define SIZE 8      /* 量化位数 */
#define CHANNELS 1  /* 声道数目 */

/* 用于保存数字音频数据的内存缓冲区 */
unsigned char buf[LENGTH*RATE*SIZE*CHANNELS/8];

int fd = -1;	/* 声音设备的文件描述符 */

static void sig_int(int signum)
{
    printf("\ncatch a SIGINT signal, you may be press Ctrl+C.\n");
    printf("ready to quit\n");

    if (fd > 0)
    {
        close(fd);
        fd = -1;
    }

    exit(0);
}

int main(int argc, char* argv[])
{
    int arg;	/* 用于ioctl调用的参数 */
    int status;   /* 系统调用的返回值 */
    
    signal(SIGINT, sig_int);
    
    /* 打开声音设备 */
    fd = open("/dev/dsp", O_RDWR);
    if (fd < 0)
    {
        perror("open of /dev/dsp failed");
        exit(1);
    }
    
    /* 设置采样时的量化位数 */
    arg = SIZE;
    status = ioctl(fd, SOUND_PCM_WRITE_BITS, &arg);
    if (status == -1)
    {
        perror("SOUND_PCM_WRITE_BITS ioctl failed");
        exit(1);
    }
    if (arg != SIZE)
    {
        perror("unable to set sample size");
        exit(1);
    }
    /* 设置采样时的声道数目 */
    arg = CHANNELS; 
    status = ioctl(fd, SOUND_PCM_WRITE_CHANNELS, &arg);
    if (status == -1)
    {
        perror("SOUND_PCM_WRITE_CHANNELS ioctl failed");
        exit(1);
    }
    if (arg != CHANNELS)
    {
        perror("unable to set number of channels");
        exit(1);
    }
    /* 设置采样时的采样频率 */
    arg = RATE;
    status = ioctl(fd, SOUND_PCM_WRITE_RATE, &arg);
    if (status == -1)
    {
        perror("SOUND_PCM_WRITE_WRITE ioctl failed");
        exit(1);
    }

    /* 循环，直到按下Control-C */
    while (1)
    {
        printf("Say something:\n");
        status = read(fd, buf, sizeof(buf)); /* 录音 */
        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");
        /* 在继续录音前等待回放结束 */
        status = ioctl(fd, SOUND_PCM_SYNC, 0); 
        if (status == -1)
            perror("SOUND_PCM_SYNC ioctl failed");
    }
}

如果不想编写代码，可以在终端输入以下命令进行测试：

cat /dev/dsp > /dev/dsp

PS：设备需要有麦克风和音频接口。实测中发现一直在“沙沙”的声音。待研究。

李迟 2017.5.31 周三