#include <avr/io.h>
#include <util/delay.h>

#define PIN_LED 0b1000;

void init_ports(void) {
  DDRB = 0x00;
  DDRC = 0x00;
  DDRD = 0x00;

  DDRD |= PIN_LED;
}

void init_pwm(void) {
  // page 84
  //  7-6: ouput A, 5-4: output B, 3-2: res, 1-0: waveform
  TCCR2A = 0b00100011;
  // 7-6: force output A/B, 5-4: res, 3: waveform, 2-0: clock source
  TCCR2B = 0b01000001;
  // duty
  OCR2B = 0;
}

void deinit_pwm(void) {
  TCCR2A = 0;
  TCCR2B = 0;
  OCR2B = 0;
}

void pwm_fade_in(int until, int step) {
  int i;
  for (i = 0; i < until; i += step) {
    OCR2B = i;
    _delay_ms(0.5);
  }
}

void pwm_fade_out(int until, int step) {
  int i;
  for (i = OCR2B; i > until; i -= step) {
    OCR2B = i;
    _delay_ms(0.25);
  }
}

int main(void) {
  init_ports();

  while (1) {
    init_pwm();
    pwm_fade_in(0x7f, 1);
    _delay_ms(300);
    OCR2B = 0xff;
    _delay_ms(150);
    pwm_fade_out(0, 4);
    deinit_pwm();
    PORTD &= ~PIN_LED;
    _delay_ms(2000);
  }
  return 0;
}