RTOS: cc2650

Tool/software: TI-RTOS

when I use many UART_write in the same function, the text and data I sent is not remain, some thing went wrong at the last of my string. Can you help me?

HERE IS MY CODE:

void read_cb(UART_Handle handle, void *rxbuff, size_t size)
{
    //uint8_t i = 0, index = 0, length = 0;
    //char data[20] = {0};


    char p1[] = "the Rx Buffer is:\r\n";
    UART_write(handle, p1, sizeof(p1));

    UART_write(handle, rxbuff, size);

    char p[] = "callback is active.\r\n";
    UART_write(handle, p, sizeof(p));

    UART_read(handle, rxbuff, size);
}

void Uart_communicate(UArg arg0, UArg arg1)
{
    //uart_init_params();
    UART_Params_init(&uartParams);
    uartParams.readMode       = UART_MODE_CALLBACK;
    //uartParams.writeMode      = UART_MODE_BLOCKING;
    //uartParams.readTimeout    = UART_WAIT_FOREVER;
    //uartParams.writeTimeout   = UART_WAIT_FOREVER;
    uartParams.readCallback   = read_cb;
    //uartParams.writeCallback  = NULL;
    //uartParams.readReturnMode = UART_RETURN_NEWLINE;
    uartParams.writeDataMode  = UART_DATA_BINARY;
    uartParams.readDataMode   = UART_DATA_BINARY;
    //uartParams.readEcho       = UART_ECHO_OFF;
    uartParams.baudRate       = 9600;
    //uartParams.dataLength     = UART_LEN_8;
    uartHandle = UART_open(Board_UART0, &uartParams);
    UART_read(uartHandle, RxBuffer, BUFF_SIZE);
    while(1)
    {
        //UART_read(uartHandle, RxBuffer, BUFF_SIZE);
        //char p[] = "the Rx Buffer is:\r\n";
        //UART_write(uartHandle, p, sizeof(p));
        //UART_write(uartHandle, RxBuffer, BUFF_SIZE);
    }
}