ALSA用户空间编程

/**alsa play test*ALSA用户空间编译，ALSA驱动的声卡在用户空间，不宜直接使用*文件接口中，而应使用alsa-lib*打开---->设置参数--->读写音频数据 ALSA全部使用alsa-lib中的API*交叉编译*export LD_LIBRARY_PATH=$PWD:$LD_LIBRARY_PATH*arm-linux-gcc -o alsa_play alsa_play_test.c -L. -lasound*需要交叉编译后的libasound.so库的支持**/#include <stdio.h>#include <stdlib.h>#include "alsa/asoundlib.h"int main(int argc, char *argv[]){int i;int ret;int buf[128];unsigned int val;    int dir=0;char *buffer;int size;snd_pcm_uframes_t frames;    snd_pcm_uframes_t periodsize;snd_pcm_t *playback_handle;//PCM设备句柄pcm.hsnd_pcm_hw_params_t *hw_params;//硬件信息和PCM流配置if (argc != 2) {printf("error: alsa_play_test [music name]\n");exit(1);}printf("play song %s by wolf\n", argv[1]);FILE *fp = fopen(argv[1], "rb");    if(fp == NULL)    return 0;    fseek(fp, 100, SEEK_SET);//1. 打开PCM，最后一个参数为0意味着标准配置ret = snd_pcm_open(&playback_handle, "default", SND_PCM_STREAM_PLAYBACK, 0);if (ret < 0) {perror("snd_pcm_open");exit(1);}//2. 分配snd_pcm_hw_params_t结构体ret = snd_pcm_hw_params_malloc(&hw_params);if (ret < 0) {perror("snd_pcm_hw_params_malloc");exit(1);}//3. 初始化hw_paramsret = snd_pcm_hw_params_any(playback_handle, hw_params);if (ret < 0) {perror("snd_pcm_hw_params_any");exit(1);}//4. 初始化访问权限ret = snd_pcm_hw_params_set_access(playback_handle, hw_params, SND_PCM_ACCESS_RW_INTERLEAVED);if (ret < 0) {perror("snd_pcm_hw_params_set_access");exit(1);}//5. 初始化采样格式SND_PCM_FORMAT_U8,8位ret = snd_pcm_hw_params_set_format(playback_handle, hw_params, SND_PCM_FORMAT_U8);if (ret < 0) {perror("snd_pcm_hw_params_set_format");exit(1);}//6. 设置采样率，如果硬件不支持我们设置的采样率，将使用最接近的//val = 44100,有些录音采样频率固定为8KHzval = 8000;ret = snd_pcm_hw_params_set_rate_near(playback_handle, hw_params, &val, &dir);if (ret < 0) {perror("snd_pcm_hw_params_set_rate_near");exit(1);}//7. 设置通道数量ret = snd_pcm_hw_params_set_channels(playback_handle, hw_params, 2);if (ret < 0) {perror("snd_pcm_hw_params_set_channels");exit(1);}/* Set period size to 32 frames. */    frames = 32;    periodsize = frames * 2;    ret = snd_pcm_hw_params_set_buffer_size_near(playback_handle, hw_params, &periodsize);    if (ret < 0)     {         printf("Unable to set buffer size %li : %s\n", frames * 2, snd_strerror(ret));             }          periodsize /= 2;    ret = snd_pcm_hw_params_set_period_size_near(playback_handle, hw_params, &periodsize, 0);    if (ret < 0)     {        printf("Unable to set period size %li : %s\n", periodsize,  snd_strerror(ret));    }  //8. 设置hw_paramsret = snd_pcm_hw_params(playback_handle, hw_params);if (ret < 0) {perror("snd_pcm_hw_params");exit(1);} /* Use a buffer large enough to hold one period */    snd_pcm_hw_params_get_period_size(hw_params, &frames, &dir);                                    size = frames * 2; /* 2 bytes/sample, 2 channels */    buffer = (char *) malloc(size);    fprintf(stderr,            "size = %d\n",            size);        while (1)     {        ret = fread(buffer, 1, size, fp);        if(ret == 0)         {              fprintf(stderr, "end of file on input\n");              break;        }         else if (ret != size)         {        }//9. 写音频数据到PCM设备        while(ret = snd_pcm_writei(playback_handle, buffer, frames)<0)        {            usleep(2000);            if (ret == -EPIPE)            {                  /* EPIPE means underrun */                  fprintf(stderr, "underrun occurred\n");  //完成硬件参数设置，使设备准备好                  snd_pcm_prepare(playback_handle);            }             else if (ret < 0)             {                  fprintf(stderr,                      "error from writei: %s\n",                      snd_strerror(ret));            }          }            }//10. 关闭PCM设备句柄snd_pcm_close(playback_handle);return 0;}