TMS570LS1224: MIBSPI is wierd

Hi, if my code is this

    uint16 TX_DATA[8] = { 0x71  };
    mibspiInit();
    while(1){
        mibspiSetData(mibspiREG1,0,TX_DATA);
        mibspiTransfer(mibspiREG1,0);
    }

I use oscilloscope, it works. But if I change code to

    uint16 TX_DATA[8] = { 0x71  };
    mibspiInit();
    mibspiSetData(mibspiREG1,0,TX_DATA);
    mibspiTransfer(mibspiREG1,0);

I cannot detect any data, any clock pulse on oscilloscope. I have no idea. Is there have some polling method transmit code for mibspi, not the HalCogen one since that's interrupt version. Thanks