void PWM4_init() {
  TCCR1 = _BV (CS10);
  GTCCR = _BV (COM1B1) | _BV (PWM1B);
  OCR1B = 127;
  OCR1C = 255;
}
void analogWrite4(uint8_t duty_value) {
  OCR1B = duty_value;
}