CCS/MSP430F5342: Variable corruption when WDT ISR running continuosly

Tool/software: Code Composer Studio

Hi,

I have some code that I have modified for product enhancements.  Part of the modification was to change the WDT (in counter mode) from being called for a timed period (to wake up the processor) to running continuously and using a counter to wake up the processor. The reason for the change was to allow 2mS time counts to be used for timing purposes.

However, in the main section of code, I call a function to read from an external RTC (below in purple, no error returned). There are no I2C bus errors and the data in the sub-function returns the correct value. However, in the calling function one of the variables within the data structure (rtcInput.dateTime.Year) is now 0 rather than 20 - rarely other elements within the data structure are corrupted. This is a irregular occasional error and is presumed to occur when the ISR is actioned during this period.

If I stop the ISR (or disable ISRs before the call and re-enable after) there are no errors.

I cannot see why the WDT ISR is corrupting the data.

Thanks
Mike

bool RTC_GetDateTime(dateTime_mS *dateTimePtr)
{
    bool retval = STATUS_SUCCESS;
    volatile dateTime_mS rtcInput = {0};

    // Read Date & Time Registers
    if (!USCI_B1_I2C_Read(RTC_SLAVE_ADD, RTC_SECONDS, sizeof(dateTime_t), (uint8_t*)&rtcInput)) retval = STATUS_FAIL;

    // This line allows a break point catch the occasional date error until cause is fixed.
    if (rtcInput.dateTime.Year == 0)
        rtcInput.dateTime.Year = 0;

// other code follows…

//*********************************************************

//This is the ISR causing the corruption...
#pragma vector=WDT_VECTOR
__interrupt void WDT_A_ISR (void)
{
    if (!--timeoutWDT)
    {
        if (!contRunning) WDT_Stop();
        LPM3_EXIT;
    }
    mSeconds += WDT_INTERVAL_mS;
    if (mSeconds>999) mSeconds = 999; 

    if(contRunning)
    {
        loopTime += WDT_INTERVAL_mS;
        if (loopTime > MAIN_LOOP_TIME)
        {
            LPM3_EXIT;
            loopTime = 0;
        }
    }
}