MSP430FR2110: how to exit LPM0/LPRM3 when

I am using the MSP430FR2110. 


I want MSP430FR2110 to exit LPM3/LPM0 when RTC interrupt is triggered and enter LPM3/LPM0 otherwise. However, RTC clock interrupt stops after short period of time. am I not using the enter and exit LPM correctly (highlighted portion of the code)?

Details regarding my application (code below), MSP430FR2110 send data throught spi when RTC interrupt is triggered. MSP430FR2110 should enter LPM3/LPM0 until next RTC interrupt event.

#include <msp430.h>


volatile static uint16_t pir_data[NUMBER_OF_CHANNELS];

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

       // set MCLK (CPU clock) to 3 MHz 
    // DCOFTRIM=3, DCO Range = 8MHz
    CSCTL1 = DCORSEL_3;

    // use default setting: digitally controller oscillator (DCO) as MCLK and SMCLK clock source 
    // set default REFO(~32768Hz) as ACLK source
    CSCTL4 = SELMS__DCOCLKDIV | SELA__REFOCLK;

    PM5CTL0 &= ~LOCKLPM5;                   // Disable the GPIO power-on default high-impedance mode
                                            // to activate previously configured port settings
    // RTC count
    RTCMOD = 320-1;
                                            // Initialize RTC
    // Source = ACLK = REFO
    SYSCFG2 |= RTCCKSEL;                    // Select ACLK as RTC clock
    RTCCTL = RTCSS_1 | RTCSR | RTCPS__1 | RTCIE;

    while(1); 
}

// RTC interrupt service routine
#if defined(__TI_COMPILER_VERSION__) || defined(__IAR_SYSTEMS_ICC__)
#pragma vector=RTC_VECTOR
__interrupt void RTC_ISR(void)
#elif defined(__GNUC__)
void __attribute__ ((interrupt(RTC_VECTOR))) RTC_ISR (void)
#else
#error Compiler not supported!
#endif
{
    switch(__even_in_range(RTCIV,RTCIV_RTCIF))
    {
        case  RTCIV_NONE:   break;          // No interrupt
        case  RTCIV_RTCIF:                  // RTC Overflow
            __bic_SR_register_on_exit(LPM3_bits);
             __bis_SR_register(GIE); 
             serial_interface_send_pir_data(pir_data);
             __bis_SR_register(LPM3_bits);
            break;
        default: break;
    }
}