void main() {
...
    // eUSCI_A0 support
    P1SEL1 &= ~(BIT4 | BIT5);
    P1SEL0 |= BIT4|BIT5;
    PMM_unlockLPM5();
...
// MCLK, SMCLK are both at 16MHz running off DCO with FLL bound to XT1 crystal
...
    // Initialize eUSCI_A0
    EUSCI_A_UART_initParam ea0Init;
    ea0Init.uartMode = EUSCI_A_UART_MODE;
    ea0Init.selectClockSource = EUSCI_A_UART_CLOCKSOURCE_SMCLK;
    ea0Init.parity = EUSCI_A_UART_NO_PARITY;
    ea0Init.overSampling = EUSCI_A_UART_OVERSAMPLING_BAUDRATE_GENERATION;
    ea0Init.msborLsbFirst = EUSCI_A_UART_LSB_FIRST;
    ea0Init.numberofStopBits = EUSCI_A_UART_ONE_STOP_BIT;
    uint32_t brDiv, brMod;
    brDiv = (16000000 << 4) / 115200;
    brMod = brDiv & 0xFFF0;
    brDiv >>= 8;
    brMod >>= 4;
    ea0Init.clockPrescalar = brDiv;
    ea0Init.firstModReg = brMod & 0x0F;
    ea0Init.secondModReg = brMod >> 4;
    EUSCI_A_UART_init(EUSCI_A0_BASE, &ea0Init);
    EUSCI_A_UART_enable(EUSCI_A0_BASE);
    EUSCI_A_UART_resetDormant(EUSCI_A0_BASE);
    EUSCI_A_UART_enableInterrupt(EUSCI_A0_BASE, EUSCI_A_UART_TRANSMIT_INTERRUPT | EUSCI_A_UART_RECEIVE_INTERRUPT);

    __enable_interrupt();
...
}

// ISR
#if defined(__TI_COMPILER_VERSION__) || defined(__IAR_SYSTEMS_ICC__)
#pragma vector=USCI_A0_VECTOR
__interrupt void USCI_A0_ISR(void)
#elif defined(__GNUC__)
void __attribute__ ((interrupt(USCI_A0_VECTOR))) USCI_A0_ISR (void)
#else
#error Compiler not supported!
#endif
{
  switch(__even_in_range(UCA0IV,USCI_UART_UCTXCPTIFG))
  {
    case USCI_NONE: break;
    case USCI_UART_UCRXIFG:
      P1OUT |= BIT0; // Switch on red LED when byte received; TX vector will switch it off, it should be a short flicker
      while(UCA0STATW&UCBUSY); // Busy-waits inside ISR is bad code, but this is a stupid simple example
      UCA0TXBUF = UCA0RXBUF;
      __no_operation();
      break;
    case USCI_UART_UCTXIFG:
      P1OUT &= ~BIT0;
      break;
    case USCI_UART_UCSTTIFG: break;
    case USCI_UART_UCTXCPTIFG: break;
    default: break;
  }
}