一个关于音频播放的fpga驱动代码。流程是从sd卡中读取音频文件，然后缓存到DDR中，再通过一定的时序关系让音频WM8731芯片播放-An audio playback on fpga driver code. The process is to read audio files from sd card and then cached to DDR, and then through a certain timing relationships allow playback of audio