CCS/TMS320F2812: about SPI

Tool/software: Code Composer Studio

Hi, Some question comes when I use the SPI interface,  when  debug in  lookback mode, the data is send, but it stops in " while(SpiaRegs.SPIFFRX.bit.RXFFST !=1) ;"always, I do not know the reason. my code is as follows:

void InitSpi(void)
{
    EALLOW;
        GpioMuxRegs.GPFMUX.all = 0x000f;
        EDIS;

   // Initialize SPI-A:
    SpiaRegs.SPICCR.bit.SPISWRESET=0; // Reset SPI
    SpiaRegs.SPICCR.all =0x0017;                 // Reset on, rising edge, 8-bit char bits
    SpiaRegs.SPICTL.all =0x0006;                 // Enable master mode, normal phase,
    SpiaRegs.SPISTS.all=0x0000;
    SpiaRegs.SPIBRR =0x007F;                      // LSPCLK/（SPIBRR+1)
    SpiaRegs.SPICCR.all =0x0087;                 // Relinquish SPI from Reset
}

Uint16 SpiReadWrite(Uint16 wdata)
{
    Uint16 rdata;

    SpiaRegs.SPITXBUF=wdata;
    while(SpiaRegs.SPIFFRX.bit.RXFFST !=1) ;
    rdata = SpiaRegs.SPIRXBUF;

     return rdata;
}