MSP430F5659: Timer A1 in capture mode -> CCIFG is never set but interrupt gets called, COV is set every two interrupts

user4725373

Part Number: MSP430F5659

Hi,

I'm using TA1 in capture mode with external capture pins driven by a PWM signal at 32.768 kHz. The CCIFG of TA1CCR0 never gets set, but I still get in the timer interrupt. One interrupt out of two, COV gets set, as if I skipped reading TA1CCR0. Here's my code:

void main(void) {

  // TA1.0
  P3SEL |= BIT1;
  P3DIR&= ~BIT1;
 
  // TA1CLK
  P3SEL |= BIT0;  
  P3DIR &= ~BIT0;

  TA1CTL = TASSEL__TACLK | ID__1 | MC__STOP;
  TA1CCTL0 = CM1 | CM0 | CAP;

  TA1R = 0;
  TA1CCTL0 &= ~COV;
  TA1CCTL0 |= CCIE;
  TA1CTL |= MC__CONTINOUS;
}

#if defined(__TI_COMPILER_VERSION__) || defined(__IAR_SYSTEMS_ICC__) || defined(__CROSSWORKS__)
#pragma vector=TIMER1_A0_VECTOR
__interrupt void isr_timer1_a0(void)
#elif defined(__GNUC__) && (__MSP430__)
void __attribute__ ((interrupt(TIMER1_A0_VECTOR))) isr_timer1_a0(void)
#endif
{
  if (TA1CCTL0 & CCIFG) {
    if (!((P3IN & BIT1) == BIT1)) {
      /* Do something */
    } else {
      /* Do something else */
    }
  } else if (TA1CCTL0 & COV) {
    TA1CCTL0 &= ~COV;
    /* Do something */
  }
}

I put a breakpoint in the interrupt and the value of TA1CCR0 keeps increasing, but the CCIFG flag is never set. Am I missing something?

Thanks,

Fred

over 7 years ago

0 Bruce McKenney over 7 years ago

Guru 96315 points

The CCIFG for CCTL0 is reset on entry to the CCR0 ISR. This happens only for CCR0.

Conversely: if you arrived at the CCR0 ISR, you know that the CCIFG was triggered (before).

0 user4725373 over 7 years ago in reply to Bruce McKenney

Expert 1645 points

So is the only cause of interruption the capture interrupt (CCIFG), and COV is only a flag that I need to check?

0 Bruce McKenney over 7 years ago in reply to user4725373

Guru 96315 points

COV is always accompanied by a capture event [User Guide SLAU367O Fig. 25-11], so it doesn't generate a CCIFG on its own.

0 user4725373 over 7 years ago in reply to Bruce McKenney

Expert 1645 points

Ok, thank you very much.

0 Britta Ruelander over 7 years ago in reply to user4725373

TI__Genius 10860 points

Hi Fred,

I'm glad to see that your question has already be answered.

The capture mode is explained and visualized in Section 17.2.4 of the Family User's Guide (SLAU208 for the device you are currently looking at) and describes both when the CCIFG is set and also in what case the COV Bit is set. You can have a look for further reference.

Please feel free to comment in case there are other open points.

Best regards,

Britta

0 Bruce McKenney over 7 years ago in reply to user4725373

Guru 96315 points

Ms Britta is gently reminding me to clean my glasses again.

As she says, in the F5 (not FR5) User Guide (SLAU208O) the figure I mentioned is Fig 17-11.

0 user4725373 over 7 years ago in reply to Bruce McKenney

Expert 1645 points

Thank you both,

Indeed, it's by looking at Figure 17-11 that I realized that my CCIFG interrupts must work if COV gets set. I just hadn't read the sentence "The TAxCCR0 CCIFG flag is automatically reset when the TAxCCR0 interrupt

request is serviced." from SLAU208.

Have a great day,

Fred

0 Britta Ruelander over 7 years ago in reply to user4725373

TI__Genius 10860 points

Hi Fred,

I'm glad to hear that the documentation clarified the situation.
Are there any open items that should be addressed here? If not please let me know so that I can close this thread.

Thanks and best regards,
Britta

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MSP430F5659: Timer A1 in capture mode -> CCIFG is never set but interrupt gets called, COV is set every two interrupts