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CC430 timer capture interrupts trapped

Bob Chou
Intellectual 530 points

Hi,

I'm using cc430 timer capture mode to do some signal frequency measurement experiments.

I set up TA0 and CCR as following register values:

    TA0CTL|=TACLR+TASSEL__TACLK+ID_0+MC__CONTINUOUS; 
    TA0CCTL2|=CCIS_1+CAP+SCS+CM_1+CCIE;     
    TA0CCTL3|=CCIS_1+CAP+SCS+CM_1+CCIE;

The Timer input is an external 10MHz clock source, CCR2|CCI2B input is ACLK/2 which is about 16kHz, CCR3|CCI3B input is GDO1 clk, which is about 135kHz.

The interrupt trigger a TA0CCRx register value reading on every 320 captures, which prolonged the measurement period. The interrupt service code is following:

static int Captures=0;
static int Captures1=0;
#define NCAPTURES 320
#define NCAPTURES1 320
#define FACLK 1.027//0.2925
#pragma vector=TIMER0_A1_VECTOR
__interrupt void TimerA(void)
{
//	 TA0CTL|=TACLR;//TASSEL__INCLK+ID_0+MC__CONTINUOUS;
   switch(__even_in_range(TA0IV,8))
   {
      case 4:
             switch(Captures){
             case 0:
                   starttime=TA0CCR2;
                   Captures=NCAPTURES;
                   break;
             case 1:
                   num1=TA0CCR2;
                   TA0CTL|=TACLR;
                   Captures=0;
                   sprintf(buffer1,"1 %lu\n",num1);
		putstr(buffer1); 
                   break;
             default:
                    Captures--;
                    break;

             }
      case 6:
             switch(Captures1){
             case 0:
                   starttime1=TA0CCR3;
                   Captures1=NCAPTURES1;
                   break;
             case 1:
                   num2=TA0CCR3;
                   TA0CTL|=TACLR;
                   Captures1=0;
		sprintf(buffer2,"2 %lu\n",num2);
		putstr(buffer2);                   
                break;
             default:
                    Captures1--;
                    break;

             }
      default:break;
   }
   __bic_SR_register_on_exit(LPM3_bits);


}

When I have only CCR2 enabled and CCR3 disabled, everything works fine. Once I enable CCR3 both capture interrupts works fine but the program trapped in the Timer interrupt and cannot jump back to the main loop. I am wondering why this happened, possible reason might be the frequency of CCR3 input is faster than the system main clock?

Thanks in advance!

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