audio的replay模式不能播放长度小于内存块大小的数据吗？

发布于 2020-09-10 11:43:19 浏览：1079 订阅该版

使用`_audio_dev_write`启动音频数据replay。从代码看，在这个函数中是要把发送的数据按照replay内存池中内存块的大小进行分割，如果数据量能够满足内存块大小，就作为一帧数据放入replay->queue中，而剩余不足一个内存块大小的数据或者要发送的数据总量小于一个内存块大小时，就不会把数据放入replay->queue，而是留在replay->write_data中。

```c
/* components/drivers/audio/audio.c */

static rt_size_t _audio_dev_write(struct rt_device *dev, rt_off_t pos, const void *buffer, rt_size_t size)
{
    ...
    
    /* push a new frame to replay data queue */
    ptr = (rt_uint8_t *)buffer;
    block_size = RT_AUDIO_REPLAY_MP_BLOCK_SIZE;

rt_mutex_take(&audio->replay->lock, RT_WAITING_FOREVER);
    while (index < size)
    {
        /* request buffer from replay memory pool */
        if (audio->replay->write_index % block_size == 0)
        {
            audio->replay->write_data = rt_mp_alloc(audio->replay->mp, RT_WAITING_FOREVER);
            memset(audio->replay->write_data, 0, block_size);
        }

/* copy data to replay memory pool */
        remain_bytes = MIN((block_size - audio->replay->write_index), (size - index));
        memcpy(&audio->replay->write_data[audio->replay->write_index], &ptr[index], remain_bytes);

index += remain_bytes;
        audio->replay->write_index += remain_bytes;
        audio->replay->write_index %= block_size;

if (audio->replay->write_index == 0)
        {
            rt_data_queue_push(&audio->replay->queue,
                               audio->replay->write_data,
                               block_size,
                               RT_WAITING_FOREVER);
        }
    }
    ...
}
```

而实际启动数据发送的过程是这样的：底层驱动先用DMA发一段全0的数据，然后在DMA完成中断中调用`_audio_send_replay_frame`发送数据，在`_audio_send_replay_frame`函数中，如果replay->queue为空，就只会发送全0数据。也就是说不足一个内存块大小的数据并没有被发送。  
```
/* components/drivers/audio/audio.c */

static rt_err_t _audio_send_replay_frame(struct rt_audio_device *audio)
{
    ...

buf_info = &audio->replay->buf_info;
    /* save current pos */
    position = audio->replay->pos;
    dst_size = buf_info->block_size;

/* check repaly queue is empty */
    if (rt_data_queue_peak(&audio->replay->queue, (const void **)&data, &src_size) != RT_EOK)
    {
        /* ack stop event */
        if (audio->replay->event & REPLAY_EVT_STOP)
            rt_completion_done(&audio->replay->cmp);

/* send zero frames */
        memset(&buf_info->buffer[audio->replay->pos], 0, dst_size);

audio->replay->pos += dst_size;
        audio->replay->pos %= buf_info->total_size;
    }
    else
    {
        ...
    }

if (audio->ops->transmit != RT_NULL)
    {
        if (audio->ops->transmit(audio, &buf_info->buffer[position], RT_NULL, dst_size) != dst_size)
            result = -RT_ERROR;
    }

return result;
}
```

**请帮忙看一下上面的理解是哪里有问题？**