CCS/MSP430FR2311: Incorrect timing when selecting VLOCLK as source for RTC.

Part Number: MSP430FR2311
Other Parts Discussed in Thread: MSP430FR4133,

Tool/software: Code Composer Studio

I am trying to use VLOCLK as clock source for the RTC module in LPM3 and use RTC interrupt to blink an LED every one second. My ultimate aim is to use RTC in LPM3.5 without any external oscillators.

Here's my code:

#include <msp430.h>

#define VLOCLK

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

#ifndef VLOCLK
    P2SEL1 |= BIT6 | BIT7;                  // P2.6~P2.7: crystal pins
    do
    {
        CSCTL7 &= ~(XT1OFFG | DCOFFG);      // Clear XT1 and DCO fault flag
        SFRIFG1 &= ~OFIFG;
    }while (SFRIFG1 & OFIFG);               // Test oscillator fault flag
#else
    // Selecting VLO as Main Osc: Refer 3.2.2 in www.ti.com/.../slau445g.pdf
    CSCTL4 |= SELMS__VLOCLK ;
    CSCTL5 &= ~VLOAUTOOFF;
    CSCTL5 |= DIVM__1;
#endif

    P1OUT &= ~BIT0;                         // Clear P1.0 output latch for a defined power-on state
    P1DIR |= BIT0;                          // Set P1.0 to output direction

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


#ifndef VLOCLK
    // RTC count re-load compare value at 32.
    // 1024/32768 * 32 = 1 sec.
    RTCMOD = 32-1;
    // Initialize RTC
    // Source = 32kHz crystal, divided by 1024
    RTCCTL = RTCSS__XT1CLK | RTCSR | RTCPS__1024 | RTCIE;
#else

    // VLOCLK frequency is 10KHz.
    // 1000/10000 * 10 = 1 sec
    RTCMOD = 10-1;

    RTCCTL |= RTCSS__VLOCLK | RTCPS__1000 | RTCIE | RTCSR;

#endif

    __bis_SR_register(LPM3_bits | GIE);     // Enter LPM3, enable interrupt
    //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
            P1OUT ^= BIT0;
            break;
        default: break;
    }
}

The LED toggles every 1.516 Seconds instead of every 1 Seconds.

Here's the screenshot of the logic analyzer connected to P1.0:

How to configure the RTC clock correctly?

EDIT:

The same code when programmed on MSP430FR4133 Launchpad, the LED toggles at 1.135 Second (Still not close to 1 second).

Attached the logic analyzer screenshot: