main.c

#include "adc.h"
#include "pwm.h"
//-------------------------------------------

//-------------------------------------------
int main(void)
{
    pwm_setup();
    for(;;){
        pwm(65535, 0, 1);
    }
return 0;   //  never reached
}

pwm.c

//-------------------------------------------
/*
PWM function
2010 - Josh Ashby
[email protected]
http://joshashby.com
http://github.com/JoshAshby
freenode - JoshAshby
*/
//-------------------------------------------
#include "pwm.h"
//setup timer1 for
int pwm_setup(void)
{
    OCR1AH = 0;
    DDRB |= (1<<1);
    DDRB |= (1<<2);
    TCCR1A = (1<<COM1A1)|(1<<WGM10);
    TCCR1B = (1<<WGM12);
    pwm_value = 0;
    TIMSK1 |= (1<<TOIE1);
    sei();
    return 1;
}
int pwm(unsigned int value, int pin, unsigned int speed)
{
    pwm_value = value;
    pwm_speed = speed;
    TCCR1B = (1<<CS10);
    return 1;
}
enum { UP, DOWN };

ISR (TIMER1_OVF_vect)
{
    unsigned int pwm;
    int direction = UP;
    switch (direction)
    {
        case UP:
            for (pwm = 0; pwm <= pwm_value; pwm += pwm_speed){
                OCR1AL = pwm;
                pwm_value_old = pwm;
            }
            break;

        case DOWN:
            for (pwm = pwm_value_old; pwm >= pwm_value; pwm += pwm_speed){
                OCR1AL = pwm;
                pwm_value_old = pwm;
            }
            break;
    }
}

pwm.h

//-------------------------------------------
/*
PWM function
2010 - Josh Ashby
[email protected]
http://joshashby.com
http://github.com/JoshAshby
freenode - JoshAshby
*/
//-------------------------------------------
#ifndef PWM_H
#define PWM_H
#include <avr/io.h>
#include <util/delay.h>
#include <inttypes.h>
#include <avr/interrupt.h>
#include <avr/sleep.h>
int pwm_start(void);
int pwm(unsigned int value, int pin, unsigned int speed);
int pwm_ramp(unsigned int value, int pin, unsigned int speed);
unsigned int pwm_value;
unsigned int pwm_speed;
unsigned int pwm_value_old;
#endif