#define F_CPU 1000000
#include <avr/io.h>
#include <util/delay.h>

#define OutputCompareRegister1 OCR1A
#define OutputCompareRegister2 OCR1B

#define PWMDDR DDRB

#define PWMpin1 PB1
#define PWMpin2 PB2

void init16bitPWM() //this function works for ATMega8 but needs to be configured for other AVR uCs (configure the registers and the bits)
{
    PWMDDR |= 1<<PWMpin1;
    PWMDDR |= 1<<PWMpin2;


    TCCR1A |= 1<<WGM11 | 1<<COM1A1 | 1<<COM1B1;
    TCCR1B |= 1<<WGM12 | 1<<WGM13 | 1<<CS10;

    ICR1 = 65535;

    OutputCompareRegister1 = 0;
    OutputCompareRegister2 = 0;
}

void changeDuty16bit(uint16_t duty, uint8_t channel)
{
    switch (channel)
    {
    case 1:
        OutputCompareRegister1=duty;
        break;
    case 2:
        OutputCompareRegister2=duty;
        break;
    }
}

int main(void)
{
    //Initialization
    init16bitPWM();

    //Variables
    int i;

    //Infinite loop
    while(1)
    {

        for (i=0;i<65536;i++)
        {
            changeDuty16bit(i,1);
            _delay_ms(10);
        }
    }
}