MSP430FR68791: Time A interrupt lost?

Klaus Schlitt

Part Number: MSP430FR68791

I use timer TA0 to measure the pulse-width of two input signals (CCR1 and CCR2) with the capture mode (Clock is SMCLK divided by 4 (4 MHz) ).For test purpose, the two input signals have the same source (366 Hz).
The measurement result is 290 Hz.

In case I disable the second interrupt (e.g. for CCR2), then the measurement is correct.
It seems to me that interrupts might be lost.
I use the do/while loop in order to handle pending interrupts as long as interrupts are still pending.

Other reason for the wrong measurement might be wrong irq source detected and so wrong CCR counter used for the measurement.

////////////////////////////////////////////////////
// Interrupt service routine for tacho interrupt  //
// interrupt is triggered with rising edge of     //
// tacho pulse. With the rising edge the current   //
// counter value is captured and stored in CCR1/2  //
////////////////////////////////////////////////////
#pragma vector=TIMER0_A1_VECTOR
__interrupt void ISR_Timer_A( void )
{
    // for debugging static int count    = 0;
    static int lastCCR[2]  = { 0, 0 };

    Uint16   currentCCRx;
    Uint8    fanNr;
    
    uint16_t ccrNr = 0xFFFF;
        
    do
    {
        switch( __even_in_range( TA0IV, 0x0E ) )
        {
            case TA0IV_TACCR1:   /* TA0CCR1_CCIFG */
                currentCCRx = TA0CCR1;
                fanNr = 0;
                ccrNr = TIMER_A_CAPTURECOMPARE_REGISTER_1;
                break;

            case TA0IV_TACCR2:   /* TA0CCR2_CCIFG */
                currentCCRx = TA0CCR2;
                fanNr = 1;
                ccrNr = TIMER_A_CAPTURECOMPARE_REGISTER_2;
                break;

            default:
                ccrNr = 0xFFFF;
                break;
        }    

        // Timer_A_clearTimerInterrupt( TIMER_A0_BASE );
        if( ccrNr!=0xFFFF )
        {
            Uint16 ccrx    = currentCCRx - lastCCR[fanNr];
            lastCCR[fanNr] = currentCCRx;

            i2cIFMemoryMap.rawTacho[fanNr] = ccrx;
            addToTachoArray( fanNr, ccrx );

            Timer_A_clearCaptureCompareInterrupt( TIMER_A0_BASE, ccrNr );

            tachoIrqCount[fanNr]++;
        }
    }while( ccrNr!=0xFFFF );
}

over 7 years ago

0 Cameron LaFollette over 7 years ago

TI__Genius 14875 points

HI Klaus,
Can you share your Timer A setup?

You shouldn't need that while loop, as the pending interrupts will generate a new flag upon exiting. See sect 25.2.6.2 of the user guide. Try removing this.

How are you dealing with timer overflow?

0 Bruce McKenney47378 over 7 years ago

Guru 89760 points

1) How long does addToTachoArray() take to run?

2) Reading TA0IV clears the relevant CCIFG. You should Not be doing this explicitly (Timer_A_clearCaptureCompareInterrupt). The hazard is that you can lose interrupts.

3) lastCCR should be declared Uint16, not int. What you have might work, but you want to be sure the subtraction (particularly modulo wraparound) is done properly.

0 Klaus Schlitt over 7 years ago in reply to Bruce McKenney47378

Prodigy 170 points

I just found the reason for the problem.

In function addToTachhoArray(), I did not consider the parameter "fanNr" for all relevant variables.
For that reason the calculation of the average tacho value did not work.

Thanks a lot for your help!

0 Klaus Schlitt over 7 years ago in reply to Cameron LaFollette

Prodigy 170 points

Hi Cameron,
thanks for that hint. I removed the while loop now.
I do not deal with timer overflows. Should I check the COV bit in register TAxCCTLn?
Meanwhile I found the reason for the problem of wrong measurement. I did not consider the "fanNr" for all relevant variables in addToTachoArray().

0 Cameron LaFollette over 7 years ago in reply to Klaus Schlitt

TI__Genius 14875 points

Klaus,
Yes, otherwise you are opening yourself up to the scenario when the new timer value will be less than the old timer value.

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MSP430FR68791: Time A interrupt lost?