McbspB to SPI mode: The receiver is always 0xFF in clock stop mode without delay

Part Number: TMS320F28335
Other Parts Discussed in Thread: C2000WARE

Hi:

    The demo code I used is "F:\C2000_SDK\C2000Ware_1_00_03_00\device_support\f2833x\examples\mcbsp_loopback_dma". I change the mcbsp_spi mode from DLB to clock stop mode. The CLK of SPI is 400KHz.

    I want to use MCBSPB as SPI mode to communicate with SD card. Here below is my configuration.

void InitMcbspbGpio(void)
{
    EALLOW;

    // Configure McBSP-A pins using GPIO regs
    // This specifies which of the possible GPIO pins will be McBSP functional
    // pins.
    // Comment out other unwanted lines.
    GpioCtrlRegs.GPAMUX1.bit.GPIO12 = 3;	    // GPIO12 is MDXB pin MOSI
    GpioCtrlRegs.GPAMUX1.bit.GPIO13 = 3;	    // GPIO13 is MDRB pin MISO
    GpioCtrlRegs.GPAMUX1.bit.GPIO14 = 3;	    // GPIO14 is MCLKXB pin CLK
    GpioCtrlRegs.GPAMUX1.bit.GPIO15 = 3;	    // GPIO15 is MFSXB pin

    // Enable internal pull-up for the selected pins
    // Pull-ups can be enabled or disabled by the user.
    // This will enable the pullups for the specified pins.
    // Comment out other unwanted lines.
    GpioCtrlRegs.GPAPUD.bit.GPIO12 = 0;	        //Enable pull-up on GPIO12 (MDXB)
    GpioCtrlRegs.GPAPUD.bit.GPIO13 = 0;	        //Enable pull-up on GPIO13 (MDRB)
    GpioCtrlRegs.GPAPUD.bit.GPIO14 = 0;	        //Enable pull-up on GPIO14 (MCLKXB)
    GpioCtrlRegs.GPAPUD.bit.GPIO15 = 0;	        //Enable pull-up on GPIO15 (MFSXB)

    // Set qualification for selected input pins to asynch only
    // This will select asynch (no qualification) for the selected pins.
    // Comment out other unwanted lines.
    GpioCtrlRegs.GPAQSEL1.bit.GPIO13 = 3; // Asynch input GPIO13 (MDRB)
    GpioCtrlRegs.GPAQSEL1.bit.GPIO14 = 3; // Asynch input GPIO14 (MCLKXB)
    GpioCtrlRegs.GPAQSEL1.bit.GPIO15 = 3; // Asynch input GPIO15 (MFSXB)

    EDIS;
}

void McbspB_init(void)
{

    EALLOW;
    SysCtrlRegs.PCLKCR0.bit.MCBSPAENCLK = 1;      // enable low speed clock to McBSP-A
    SysCtrlRegs.PCLKCR0.bit.MCBSPBENCLK = 1;      // enable low speed clock to McBSP-B
    EDIS;

    // Reset FS generator, sample rate generator & transmitter
    McbspbRegs.SPCR2.all=0x0000;
    McbspbRegs.SPCR1.all=0x0000;                 // Reset Receiver, Right justify word
    McbspbRegs.PCR.all = 0xF08;                  // CLKXM = CLKRM = FSXM = FSRM = 1, FSXP = 1

    // clocking scheme:
    //McbspbRegs.MFFINT.all=0x0;                 // Disable all interrupts
    McbspbRegs.SPCR1.bit.CLKSTP = 2;             // clock stop mode, without clock delay
    McbspbRegs.PCR.bit.CLKXP = 1;                // transmit data are sampled on the rising edge of clock signal
    McbspbRegs.PCR.bit.CLKRP = 0;                // receive data are sampled on the falling edge of clock signal

    McbspbRegs.RCR2.bit.RDATDLY = 1;             // 1 for master mode, 0 for slave mode (?)
    McbspbRegs.XCR2.bit.XDATDLY = 1;             // 1 for master mode, 0 for slave mode (?)

    McbspbRegs.RCR1.bit.RWDLEN1 = 0;             // 8-bit word
    McbspbRegs.XCR1.bit.XWDLEN1 = 0;             // 8-bit word


    McbspbRegs.SRGR2.all = 0x2000;               // CLKSM = 1, FPER = 1 CLKG period
     //               LSPCLK
     // CLKG_freq = ----------
     //             CLKGDV + 1
    //McbspbRegs.SRGR1.all = 0x000F;             // frame width = 1 CLKG period, CLKGDV = 15 (2.34 MHz)
    McbspbRegs.SRGR1.all = 95;               // frame width = 1 CLKG period, CLKGDV = 5 (6.25 MHz)
    //
    // Enable Sample rate generator
    //
    McbspbRegs.SPCR2.bit.GRST=1;    // Enable the sample rate generator
    delay_loop();                   // Wait at least 2 SRG clock cycles
    McbspbRegs.SPCR2.bit.XRST=1;    // Release TX from Reset
    McbspbRegs.SPCR1.bit.RRST=1;    // Release RX from Reset
    McbspbRegs.SPCR2.bit.FRST=1;    // Frame Sync Generator reset
}

I need use 400Khz CLK to send cmd to init SD card. However, no matter what I send in "DXR1", the receive reg"DRR1" will always be 0xFF. 

Is there anything wrong with my MCBSP configuration?

By the way, I can not do loop back test becasue the hardwire circuit is fixed. Also, I have disabled tx and rx interrupt, is that matter?