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在alsa驱动源码pcm部分,有一个对pcm操作的函数指针列表,其中的内容如下:
struct file_operations snd_pcm_f_ops[2] = {
{
.owner = THIS_MODULE,
.write = snd_pcm_write,
.writev = snd_pcm_writev,
.open = snd_pcm_playback_open,
.release = snd_pcm_release,
.poll = snd_pcm_playback_poll,
.unlocked_ioctl = snd_pcm_playback_ioctl,
.compat_ioctl = snd_pcm_ioctl_compat,
.mmap = snd_pcm_mmap,
.fasync = snd_pcm_fasync,
},
{
.owner = THIS_MODULE,
.read = snd_pcm_read,
.readv = snd_pcm_readv,
.open = snd_pcm_capture_open,
.release = snd_pcm_release,
.poll = snd_pcm_capture_poll,
.unlocked_ioctl = snd_pcm_capture_ioctl,
.compat_ioctl = snd_pcm_ioctl_compat,
.mmap = snd_pcm_mmap,
.fasync = snd_pcm_fasync,
}
};
其中的放音部分,是否是先用snd_pcm_playback_open打开音频设备,再用snd_pcm_write向声卡中写数据就可以放音了呢?(在标准的alsa中对于应用层的编程是通过alsa-lib封装上述部分以实现的)
现在我不用alsa-lib就直接采用上述方法能行吗?
如果回答是肯定的,在我测试的过程中snd_pcm_playback_open是成功了的返回为0,substream->runtime->status->state的状态是打开的(SNDRV_PCM_STATE_OPEN).但是在snd_pcm_write中却出现了问题,如下:
if (runtime->status->state == SNDRV_PCM_STATE_OPEN) {
result = -EBADFD;
goto end;
}
运行这段代码后就退出了程序,不能向设备里面写入音频流.请问各位牛人这是怎么回事?能指教下小弟吗?
[ 本帖最后由 zzhhzr 于 2008-10-6 14:57 编辑 ] |
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