CCS/TMS320F28377S: 28377 McBSP work as SPI master the transmit problem

Tool/software: Code Composer Studio

I want to use the McBSP,and config it as SPI,and now,the SPI can work in correct timing sequence,but I cannot transmit what I want to.

This is I want:one frame has 6 words,each words has 8-bit.

I do not know how to transmit my data(for example:0x123456789ABC). And the wave should like figure 1(I missed  one word in the fig ).

But now, what I can see in the logic analyzer is like :

this is my transmit part code:

    char x[6]={0x12,0x34,0x56,0x78,0x9a,0xbc};
    for(i=0;i<6;i++)
    {    
    while( McbspbRegs.SPCR2.bit.XRDY == 1 )
    {McbspbRegs.DXR1.all=x[i];}
    DELAY_US(15);
    }

if I do not use the DELAY_US function,the wave shape is:

it is 7 words,but all words are same.

if I write transmit once,it will send 6 words but but all words are same.

I dont know how to transmit and config the register or is there wrong with my config?

My code like this:

    McbspbRegs.SPCR2.all=0x0000;         // Reset FS generator, sample rate generator & transmitter
    McbspbRegs.SPCR1.all=0x0000;         // Reset Receiver, Right justify word, Digital loopback dis.
    McbspbRegs.PCR.all=0x0F08;           //(CLKXM=CLKRM=FSXM=FSRM= 1, FSXP = 1)
    McbspbRegs.SPCR1.bit.DLB = 0;
    McbspbRegs.SPCR1.bit.CLKSTP = 3;     // Together with CLKXP/CLKRP determines clocking scheme
    McbspbRegs.PCR.bit.CLKXP = 0;        // CPOL = 0, CPHA = 0 rising edge no delay
    McbspbRegs.PCR.bit.CLKRP = 0;
    McbspbRegs.RCR2.bit.RDATDLY=0;      
    McbspbRegs.XCR2.bit.XDATDLY=0;      
    McbspbRegs.RCR2.bit.RFIG=1;      
    McbspbRegs.XCR2.bit.XFIG=1;      

    McbspbRegs.RCR1.bit.RWDLEN1=0;       // 8-bit word
    McbspbRegs.XCR1.bit.XWDLEN1=0;       // 8-bit word
    McbspbRegs.RCR1.bit.RFRLEN1=6;       // 6 word
    McbspbRegs.XCR1.bit.XFRLEN1=6;       // 6 word

    McbspbRegs.SRGR2.all=0x2000;         // CLKSM=1, FPER = 1 CLKG periods
    McbspbRegs.SRGR1.all= 0x0063;        // Frame Width = 1 CLKG period, CLKGDV=

    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

  Is there anyone can give me some advice or some example code I can refer to?? thank you!!