请教一个IIS接口播放音频的问题

只看该作者 · 2007-5-8 11:36

    以下是我写的一段通过IIS接口播放音频的程序

void BoFangYinPing(U32 Addr)
{
    U16 *buf;
    U16 *buf_tmp;
    U32 size;
    U8 i;

    buf = (U16 *)Addr;
    buf_tmp = buf + 22;
    size = (*(buf + 21) << 16) | *(buf + 20);

    pllcon_save =  rPLLCON;

    rPLLCON = (0x69 << 12) | (0x17 << 4) | 0;  //如果不屏蔽不可播放
    Delay(10);

    rIISCON=0x02;
    //IIS interface enable: no
    //IIS prescaler enable: yes
    //receive channel idle command: IISLRCK is generated
    //transmit channel idle command: IISLRCK is generated
    //receive DMA service request enable:no
    //transmit DMA service request enable:no

    //Master,Tx,L-ch=low,iis,16bit ch.,codeclk=256fs,lrck=32fs    rIISMOD=0x89;
    //Serial bit clock frequency slect:32fs
    //Master clock(CODECLK) frequency select:256fs
    //Serial data bit per channel:16 bit
    //Serial interface format: IIS compatible format
    //Active level of left/right channel:Low for left channel ( high for right channel)
    //Transmit/rec.eive mode select:transfer mode
    //Master/slave mode:master mode

    //Prescaler_A/B enable, value=3
    rIISPSR=0x33;
    //prescaler value B:3
    //Prescaler value A:3

    //Tx/Rx normal,Tx FIFO enable--> start piling....
    rIISFCON=0x200;
    //receive fifo enable:no
    //transmit fifo enable:yes
    //receive fifo access mode:normal access mode
    //transmite access mode select:normal access mode

    /****** IIS Tx Start ******/
    rIISCON |=0x1;
    while(Uart_Getch() != ESC_KEY)
   {
        if(IIS_FIFOREADY)
        {
              for(i=0;i<8;i++)
              {
             *rIISFIF = *buf_tmp++;
              }
              if( ((U32)buf_tmp-(U32)(buf+22)) > size )
              {
        buf_tmp = (U16 *)(buf+22);
        WrUTXH0('#');
           }
        }
    }
/****** IIS Tx Stop ******/

       rIISCON=0x0;    //IIS stop

    rPLLCON = pllcon_save;
    Delay(10);

}
一开始总是不能播放音频，经过检查，我发现问题出在Uart_Printf()函数。这个函数原先是这样定义的
char Uart_Getch(void)
{
      while(!(rUTRSTAT0 & 0x1)); //Receive data ready
      return RdURXH0();
}
如果改为
char Uart_Getch(void)
{
     if(rUTRSTAT0 & 0x1)  //Receive data ready
     return RdURXH0();
}
就可以播放音频了。

两种写法，逻辑上是一样的啊，为什么会有这么大的区别呢？
请高手指教，不胜感谢！