MSP430F5529: Using the UART on the MSP430EXPF5529 launchpad to echo characters using the driverlib

Hi,

I have been trying to use my launchpad board's UART capabilities to echo characters on the serial terminal. The code below works ONLY if I debug the program. That is, if I use the debug option in the code composer studio, let the program load and then press continue without adding any breakpoints, the code works as long as I am still debugging.

As soon as I stop debugging, that is, get out of the debug mode in CCS, I start seeing garbage character '▒' on the serial terminal, whatever I type. Similarly, if I try to directly load the program instead of going into a debug session. I am facing the same problem. I use driverlib and here is my code.

I toggle an LED to see if the code enters the interrupt. It does that everytime I press a key, but the board just returns garbage value from the interrupt.

#include "driverlib.h"
void GPIO_init(void);
void UART_init(void);

uint8_t receivedData;
uint8_t transmitData;

void main(void) {
    WDT_A_hold(WDT_A_BASE);
    GPIO_init();
    UART_init();
    __delay_cycles(1000); // I read somewhere that this helps. I don't see why. 

    //Enable UART module for operation
    USCI_A_UART_enable(USCI_A1_BASE);

    // Receive interrupt
    USCI_A_UART_enableInterrupt(USCI_A1_BASE, UCRXIE);

    __bis_SR_register(LPM3_bits+GIE);
    __no_operation();



}

void GPIO_init()
{
    // initialize GPIO pins
        // We need to setup the two GPIO points to their right functions and toggle the values
        // Clear GPIO interrupt
        P3DIR=0xFF;
        P3OUT&=0x00;
        P4DIR=0xFF;
        P4OUT&=0x00;
        P1DIR=0xFF;
        P1OUT&=0x00;

        //Set up LED PIN
        GPIO_setAsOutputPin(GPIO_PORT_P1, GPIO_PIN0);
        GPIO_setAsOutputPin(GPIO_PORT_P4, GPIO_PIN7);
        GPIO_setOutputLowOnPin(GPIO_PORT_P1, GPIO_PIN0);
        GPIO_setOutputLowOnPin(GPIO_PORT_P4,GPIO_PIN7);

        // Set GPIO for alternate function
        GPIO_setAsPeripheralModuleFunctionInputPin(GPIO_PORT_P4, GPIO_PIN5); // UART RX as an alternate function for p4.5
        GPIO_setAsPeripheralModuleFunctionOutputPin(GPIO_PORT_P4, GPIO_PIN4);//UART TX as an alternate function for p4.4

}

void UART_init()
{ // Here I am not sure if my values for clock prescalar, firstmodreg, secondmodreg are correct.
  


    USCI_A_UART_initParam param1 = {0};
    param1.selectClockSource = USCI_A_UART_CLOCKSOURCE_SMCLK;
    param1.clockPrescalar = 6; // Values for 9600 baud rate
    param1.firstModReg = 13; // Values for 9600 baud rate
    param1.secondModReg = 0; // Values for 9600 baud rate
    param1.parity = USCI_A_UART_NO_PARITY;
    param1.msborLsbFirst = USCI_A_UART_LSB_FIRST;
    param1.numberofStopBits = USCI_A_UART_ONE_STOP_BIT;
    param1.uartMode = USCI_A_UART_MODE;
    param1.overSampling = USCI_A_UART_OVERSAMPLING_BAUDRATE_GENERATION;

    if (STATUS_FAIL == USCI_A_UART_init(USCI_A1_BASE, &param1)){
        return;
    }



}

#pragma vector=USCI_A1_VECTOR
__interrupt void USCI_A1_ISR(void)
{
    switch(__even_in_range(UCA1IV,4))
    {
    case 2:
        // Echo back RXed character, confirm TX buffer is ready first


        // Wait if either transmit or receive is happening

        while(USCI_A_UART_queryStatusFlags(USCI_A1_BASE, UCBUSY));
        // Receive echoed data
        receivedData=USCI_A_UART_receiveData(USCI_A1_BASE);
        transmitData=receivedData;

        while(USCI_A_UART_queryStatusFlags(USCI_A1_BASE, UCBUSY));
        while(!USCI_A_UART_getInterruptStatus(USCI_A1_BASE, UCTXIFG));
        USCI_A_UART_transmitData(USCI_A1_BASE,transmitData);
        GPIO_toggleOutputOnPin(GPIO_PORT_P1, GPIO_PIN0); // Toggle LED to show it enters interrupt


        break;

    default:

        break;



    }
}

My first thought was it had something to do with the baud rate calculation. However, if I try other values to set the baud rates I don't even read the garbage character at the terminal.