CCS/CC2640R2F: CC2640R2F SPI Slave receive first data wrong

Tool/software: Code Composer Studio

CCS import projcec:

C:\ti\simplelink_cc2640r2_sdk_2_30_00_28\examples\rtos\CC2640R2_LAUNCHXL\drivers\spislave

SPI master main code:(not cc2640r2f)

spi_init();//CPOL=0, CPHA=1

cs_low();//CS connect to CC2640R2_LAUNCHXL_SPI_MASTER_READY of CC2640R2F

delay_ms(100);

spi_send_recv(master_tx, master_rx, 30);//master_tx[30]={0,1,2,3,...,28,29}

delay_ms(100);

cs_high();

SPI Slave main code:

//CC2640R2_LAUNCHXL.h
#define CC2640R2_LAUNCHXL_SPI0_MISO             IOID_6          /* RF1.20 */
#define CC2640R2_LAUNCHXL_SPI0_MOSI             IOID_3          /* RF1.18 */
#define CC2640R2_LAUNCHXL_SPI0_CLK              IOID_2          /* RF1.16 */
#define CC2640R2_LAUNCHXL_SPI0_CSN              PIN_UNASSIGNED

typedef enum CC2640R2_LAUNCHXL_GPIOName {
    CC2640R2_LAUNCHXL_SPI_MASTER_READY = 0,
    CC2640R2_LAUNCHXL_SPI_SLAVE_READY,

    CC2640R2_LAUNCHXL_GPIOCOUNT
} CC2640R2_LAUNCHXL_GPIOName;

///////////////////////////////////////////////////////////////////////////////////////////
///////////////////////////////////////////////////////////////////////////////////////////

//CC2640R2_LAUNCHXL.c
GPIO_PinConfig gpioPinConfigs[] = {
    IOID_0 | GPIO_DO_NOT_CONFIG,  /* CC2640R2_LAUNCHXL_SPI_MASTER_READY */
    IOID_1 | GPIO_DO_NOT_CONFIG,  /* CC2640R2_LAUNCHXL_SPI_SLAVE_READY */
};

const PIN_Config BoardGpioInitTable[] = {
    CC2640R2_LAUNCHXL_SPI0_MOSI | PIN_INPUT_EN | PIN_PULLDOWN,  /* SPI master out - slave in */
    CC2640R2_LAUNCHXL_SPI0_MISO | PIN_INPUT_EN | PIN_PULLDOWN,  /* SPI master in - slave out */
    CC2640R2_LAUNCHXL_SPI0_CLK | PIN_INPUT_EN | PIN_PULLDOWN,  /* SPI clock */

    PIN_TERMINATE
};

///////////////////////////////////////////////////////////////////////////////////////////
///////////////////////////////////////////////////////////////////////////////////////////

//spislave.c
#define SPI_MSG_LENGTH  (30)
#define SEND_MSG      ("Hello from slaver, msg#: 1")

uint8_t RxBuffer[SPI_MSG_LENGTH];
uint8_t TxBuffer[SPI_MSG_LENGTH];

void transferCompleteFxn(SPI_Handle handle, SPI_Transaction *transaction)
{
    sem_post(&Sem);
}

void *masterThread(void *arg0)
{
    SPI_Handle      Spi;
    SPI_Params      spiParams;
    SPI_Transaction transaction;
    bool            transferOK;
    int32_t         status;

    GPIO_setConfig(Board_SPI_MASTER_READY, GPIO_CFG_INPUT);
    status = sem_init(&Sem, 0, 0);
    if (status != 0) {
        while(1);
    }

    SPI_Params_init(&spiParams);
    spiParams.frameFormat = SPI_POL0_PHA1;
    spiParams.mode = SPI_SLAVE;
    spiParams.transferCallbackFxn = transferCompleteFxn;
    spiParams.transferMode = SPI_MODE_CALLBACK;
    Spi = SPI_open(CC2640R2_LAUNCHXL_SPI0, &spiParams);
    if (Spi == NULL) {
        while (1);
    }

    strncpy((char *)TxBuffer, SEND_MSG, SPI_MSG_LENGTH);
    memset((void *) RxBuffer, 0, SPI_MSG_LENGTH);

    while (GPIO_read(Board_SPI_MASTER_READY)) {}

    transaction.count = SPI_MSG_LENGTH;
    transaction.txBuf = (void *) TxBuffer;
    transaction.rxBuf = (void *) RxBuffer;
    transferOK = SPI_transfer(Spi, &transaction);
    if (transferOK) {
        sem_wait(&Sem);
    }
    else {
        while(1);
    }

    SPI_close(Spi);
    while(1);
}

Logic analyzer:(MOSI is not connected to logic analyzer)

Result:

SPI Master Sent:master_tx[30]={0,1,2,3,...,28,29}

                   Received:master_rx[30]="\0ello from slaver, msg#: 1"     //why first byte is 0x00,others bytes are correct

SPI Slave Sent: tx[30] = "Hello from slaver, msg#: 1"

                 Received: rx[30] = {0,1,2,3,...,28,29}        //Correct

Why SPI Master receive first byte is 0x00,where am I wrong