AVR Freaks

#include 
#include 
#include 

#define HZ_LO 50
#define HZ_HI 150
#define TIMER_TICK_NS 833


#define OCR_LO (uint8_t)32
#define OCR_HI (uint8_t)247
#define OCR_RANGE (OCR_HI - OCR_LO)
#define PERIOD_MAX ((1000000000UL/HZ_LO)/TIMER_TICK_NS)
#define PERIOD_MIN ((1000000000UL/HZ_HI)/TIMER_TICK_NS)
#define PERIOD_RANGE (PERIOD_MAX - PERIOD_MIN)
#define OCR_SCALE (PERIOD_RANGE/OCR_RANGE)


volatile uint16_t alc_period=0;
volatile uint16_t alc_pulse_length=0;


volatile uint16_t timer200us=0;

ISR(TIM0_OVF_vect)
{
	timer200us++;
}


ISR(PCINT0_vect)
{
	static uint32_t last_lo_ts = 0;
	static uint32_t last_hi_ts = 0;
	uint16_t timer = timer200us<<8;
	
	timer |= TCNT0;
	
	if(PINB&(1<<PINB4))
	{
		/* Pin state rising */
		alc_period = timer - last_hi_ts;
		last_hi_ts = timer;
	}
	else
	{
		/* Pin state falling */
		alc_period = timer - last_lo_ts;
		last_lo_ts = timer;
		alc_pulse_length = timer - last_hi_ts;
		
	}


}

void init_hardware(void)
{
	/* Enable interrupt for PWM input (PB4) */
	PCMSK |= (1<<PCINT4);

	/* Clear pending interrupts */
	GIFR |= (1<<PCIF);

	/* Enable Pin change interrupt */
	GIMSK |= (1<<PCIE);
	
	TIFR0 &= ~(1<<TOV0);

	/* Enable timer overflow interrupt */
	TIMSK0 |= (1<<TOIE0);

	/* Fast PWM mode */
	TCCR0A |= (1<<WGM01) | (1<<WGM00);

	/* Set OC0A on Compare Match, clear OC0A at TOP; Set OC0B on Compare Match, clear OC0B at TOP; presacler 4 */
	TCCR0A |= (1<<COM0A1) | (0<<COM0A0) | (1<<COM0B1) | (0<<COM0B0);
	
	TCCR0B |= (1<<CS01)|(0<<CS00);
	
	DDRB |= (1 << PINB0) | (1<<PINB1);
	
	PORTB |= (1<<PINB0) | (1<<PINB1);
} 


int main(void)
{
	uint16_t temp = 0;
	uint16_t pros = 0;
	


	init_hardware();
	sei();
	
	
	while(1)
	{
		pros = alc_period;
		if(pros < PERIOD_MIN) pros = PERIOD_MIN;
		if(pros > PERIOD_MAX) pros = PERIOD_MAX;
		
		temp = (PERIOD_MAX-pros)/OCR_RANGE;
		
		OCR0B = (uint8_t)(OCR_LO + temp);
	}

}