AVR Freaks

#define F_CPU 8000000

volatile uint8_t Capture;
volatile uint16_t PulseWidth;		//Kept in memory, not forgotten until re-written
volatile uint8_t TimeOut = 62;		//62 = 0.50592 second. (((1/(F_CPU/Prescaler)) * 255) * 62) = 0.50592
volatile uint8_t prev,curr;
volatile uint8_t startup_count = 2;
volatile uint8_t pulse = 0;


ISR(TIMER0_OVF_vect)
{
	//Stop de-incrementing if it is zero. Done as a precaution
	if (TimeOut)
	{
		TimeOut--;

		if (TimeOut == 0)
		{
			startup_count = 2; // Reset the capture machine
			pulse = 0;
		}
	}
}

ISR(PCINT0_vect)
{
	//Store here to get the most accurate time.
	curr = TCNT0;

	// Because i want to count the wavelength i only trigger each time its set
	if (bit_is_set(PINB, 0))
	{		
		//If pulsewidth is within 0 - 255 TCNT0 timer use this code
		if(TimeOut == 62)
		{
			PulseWidth = curr - prev;
		}
		else
		{	//Pulsewidth is over two timers
			//First add (255 - prev) because its the first portion from prev to 255
			//Second add (((62 - 1) - TimeOut) * 255)
			//(62 - 1) 1 removed due to the first overflow cant be counted or it will be 255 out
			//TimeOut) * 255) add all of the overflows towards final time
			//Third add curr as its the remaining 0 to curr
			PulseWidth = ((255 - prev) + (((62 - 1) - TimeOut) * 255) + curr;
		}
		
		prev = curr;
		
		//The first two captures will be thrown away because they will be wrong.
		if (startup_count)
		{
			startup_count--;
		}
		else
		{
			Capture = 1;
		}
	}
}

int main(void)
{
	//Setup Pin Change Interrupt
	PCMSK |= (1<<PCINT0);	//Enable this pin only (PB0)
	GIMSK |= (1<<PCIE);		//Enable Pin change interrupt
	
	//Setup Timer
	TCCR0B |= (1<<CS02);	//256 prescaler
	TIMSK |= (1<<TOIE0);	//Enable Overflow interrupt
	
	sei();					//Enable interrupts

	for(;;)
	{
		if (Capture)
		{
		    TimeOut = 62;			//Reset timeout feature
		    Capture = 0;			//Reset flag for next capture.
		    cli();					//Disabling interrupts stops atomicity. No chance to reading while writing.
		    pulse = PulseWidth;		//Disabled interrupts around this for fastest possible capture times.
		    sei();
		    
	    }
		
		//If TimeOut == 0 store to eeprom etc
	}
}