AM5708: PRU-UART

Part Number:AM5708

Hi,

I am trying to use the PRU - UART0, I refer to the pru-software-support-package/examples/am335x/PRU_Hardware_UART project, also carried out in accordance with the manual AM5708 datasheet (Section 30.7.3.7) to initialize the UART , But pr1_uart0_rxd and pr1_uart0_txd have no output ,both pins are 3.3v . And I've closed the loopback register. So I don't know what went wrong. Does the IO port need any special PinMux configuration? What should I do now? 

The relevant code:

   /*init*/
    CT_UART.DIVISOR_REGISTER_LSB_ = 104;
    CT_UART.DIVISOR_REGISTER_MSB_ = 0;
    CT_UART.MODE_DEFINITION_REGISTER = 0x0;
    CT_UART.INTERRUPT_ENABLE_REGISTER = 0x7;
    CT_UART.INTERRUPT_IDENTIFICATION_REGISTER_FIFO_CONTROL_REGISTER = (0x8) | (0x4) | (0x2) | (0x1);
    CT_UART.LINE_CONTROL_REGISTER = 3;
    CT_UART.MODEM_CONTROL_REGISTER = 0; //disable loopback
    CT_UART.POWERMANAGEMENT_AND_EMULATION_REGISTER = 0x6001;
    /*send*/
    /* Priming the 'hostbuffer' with a message */
    hostBuffer.data[0] = 'H';
    hostBuffer.data[1] = 'e';
    hostBuffer.data[2] = 'l';
    hostBuffer.data[3] = 'l';
    hostBuffer.data[4] = 'o';
    hostBuffer.data[5] = '!';
    hostBuffer.data[6] = '\0';
    /* Let's send/receive some dummy data */
    for (cnt = 0; cnt < MAX_CHARS; cnt++) {
        /* Load character, ensure it is not string termination */
        if ((tx = hostBuffer.data[cnt]) == '\0')
            break;
        CT_UART.RBR_THR_REGISTERS = tx;
        /* Wait for TX FIFO to be empty */
        while (!((CT_UART.INTERRUPT_IDENTIFICATION_REGISTER_FIFO_CONTROL_REGISTER & 0x2) == 0x2))
            ;
    }
    /*Read Data*/
    for (cnt = 0; cnt < MAX_CHARS; MAX_CHARS) {
        if ((CT_UART.LINE_STATUS_REGISTER & 0x1) != 0) {
            buffer[cnt] = CT_UART.RBR_THR_REGISTERS;
        }
    }
    /*Uart end*/