MSP430FR2433: SPI Slave not generating interrupts but works in polling mode

Hello,

I am new to MSP430s and trying to figure out how to setup MSP430FR2433 as a slave (in loop back mode to verify operation). I am using MSP-EXP430FR2433 Dev kit.

Using example code from SLAC700e (msp430fr243x_euscia0_spi_10.c), loopback fails.

example code from SLAC700e:

#include <msp430.h>

int main(void)
{
WDTCTL = WDTPW|WDTHOLD; // Stop watchdog timer

P1SEL0 |= BIT4 | BIT5 | BIT6; // set 3-SPI pin as second function

UCA0CTLW0 |= UCSWRST; // **Put state machine in reset**
UCA0CTLW0 |= UCSYNC|UCCKPL|UCMSB; // 3-pin, 8-bit SPI slave
// Clock polarity high, MSB
UCA0CTLW0 |= UCSSEL__SMCLK; // SMCLK
UCA0BR0 = 0x01; // /1, fBitClock = fBRCLK/UCBRx
UCA0BR1 = 0; //
UCA0MCTLW = 0; // No modulation
UCA0CTLW0 &= ~UCSWRST; // **Initialize USCI state machine**
UCA0IE |= UCRXIE; // Enable USCI_A0 RX interrupt

PM5CTL0 &= ~LOCKLPM5; // Disable the GPIO power-on default high-impedance mode
// to activate previously configured port settings

__bis_SR_register(LPM0_bits | GIE); // Enter LPM0, enable interrupts
}

#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
{
while (!(UCA0IFG&UCTXIFG)); // USCI_A0 TX buffer ready?
UCA0TXBUF = UCA0RXBUF; // Echo received data
}

Output from master:

00 00

00 00

00 00

00 00

But in polling mode, the slave works just fine:

#include <msp430.h>
unsigned char RXData0 = 0;
unsigned char RXData1 = 0;
unsigned char TXData = 0xAA;
unsigned char counter = 0;

int main(void)
{
WDTCTL = WDTPW | WDTHOLD; // Stop watchdog timer

P1SEL0 |= BIT4 | BIT5 | BIT6; // set 3-SPI pin as second function

UCA0CTLW0 |= UCSWRST; // **Put state machine in reset**
UCA0CTLW0 |= UCSYNC | UCCKPL | UCMSB; // 3-pin, 8-bit SPI slave
// Clock polarity high, MSB
UCA0CTLW0 |= UCSSEL__SMCLK; // SMCLK
UCA0BR0 = 0x01; // /1, fBitClock = fBRCLK/UCBRx
UCA0BR1 = 0; //
UCA0MCTLW = 0; // No modulation
UCA0CTLW0 &= ~UCSWRST; // **Initialize USCI state machine**
UCA0IE |= UCRXIE; // Enable USCI_A0 RX interrupt

PM5CTL0 &= ~LOCKLPM5; // Disable the GPIO power-on default high-impedance mode
// to activate previously configured port settings

// __bis_SR_register(LPM0_bits | GIE); // Enter LPM0, enable interrupts
while (1)
{
if (UCA0IFG & UCRXIFG)
{
if (counter == 0)
{
RXData0 = UCA0RXBUF;
while (!(UCA0IFG & UCTXIFG))
;
UCA0TXBUF = RXData0;
counter = 1;
}
else
{
RXData1 = UCA0RXBUF;
while (!(UCA0IFG & UCTXIFG))
;
UCA0TXBUF = RXData1;
counter = 0;
}
}
}

}

Output from master:

00 00

11 AA

12 AB

13 AC

14 AD

15 AE

16 AF

17 B0

18 B1

19 B2

I know the interrupt flag is enabled. I dont know why the ISR is never called. Any suggestions would be appreciated!

Thanks

Gaurav