MSP430 Pulse Width Capture

Hi all,

I'm having some troubles getting the timer interrupt to work in the way I want it to and I was hoping someone here would be able to give me some advice on where I'm going wrong.

I have a pulse input with varying duty cycle on pin 1.1 what I want my code to do is light up the LED on pin 1.0 when the duty cycle is above 50% and turn it off when it is below 50%.

I think the trouble I am having is understanding when the interrupt is 'triggered' and how I can get it to trigger on the rising and falling edge.

please see the code I am using below.

#include <msp430.h>

unsigned int Ton=0;
unsigned int Toff=0;
unsigned int TTotal =0;
unsigned int first_pulse=0;


int main(void)
{
  volatile unsigned int i;
  WDTCTL = WDTPW + WDTHOLD;                 // Stop watchdog timer
  for (i=0; i<20000; i++)                   // Delay for crystal stabilization
  {
  }
  P1DIR = 0x01;                             // Set P1.0 out,1.1 input dir
  P1OUT &= ~0x01;                           // LED off
  P1SEL = 0x02;                             // Set P1.1 to TA0
  //P2DIR = 0x01;                             // P2.0-ACLK
  //P2SEL |= 0x01;
  BCSCTL1 |= DIVA_3;                        // ACLK/8

  CCTL0 = CM_1 + SCS + CCIS_0 + CAP + CCIE; // Rising edge + CCI0A (P1.1)
                                            // + Capture Mode + Interrupt

  TACTL = TASSEL_2 + MC_2;                  // SMCLK + Continuous Mode

  _BIS_SR(LPM0_bits + GIE);                 // LPM0 + Enable global ints
}

#pragma vector=TIMERA0_VECTOR
__interrupt void TimerA0(void)
{
	if (first_pulse==0)  //detect first falling edge
	        {
	            Ton=TACCR0;    //take current value of Timer Register and store it in integer 'Ton'
	            first_pulse=1;   //set the first pulse flag to 1.
	           // goto here;
	        }

	TTotal = TACCR0;  // on next interrupt (rising edge) capture the timer register value and store it in 'TTotal'

	Toff = TTotal - Ton;   // calculate the amount of time off by subtracting Time on from Total Time.

	if(Ton >= Toff){      //if the amount of time on is greater than the amount of time off (duty cycle = >50%) then set p1.0 (light up red led)

		P1OUT |= 0x01;
		first_pulse=0;  //reset first pulse flag
	}
	else
	{
		P1OUT &= ~0x01;
	}

	//here:
	    //P1OUT^=LED1;

	}

Any advice would be appreciated.