#define DUTY_INC    0x80 
char buff[20];
uint16_t duty;
const byte pwmPin = 11; // Arduino pin 9 (OC1A) supports Timer1 PWM

void setup() {
  Serial.begin(9600);
  pinMode(pwmPin, OUTPUT); // Set the PWM pin as an output
  Serial.println("Tutorial 4");
  Serial.println("Color Cube");
  Serial.println("Skyboard v2");
  Serial.println("Pin 11 to the LED");
  Serial.print("> ");
  // Configure Timer1 for Fast PWM mode, non-inverting output
  // WGM13, WGM12, WGM11, WGM10 = 1110 for Fast PWM with ICR1 as TOP
  TCCR1A = (1<<COM1A1) | (1<<WGM11); // Clear OC1A on Compare Match, set at TOP
  TCCR1B = (1<<WGM13) | (1<<WGM12) | (1<<CS11); // Fast PWM mode 14, prescaler 8
  // Set the TOP value for the timer (determines PWM frequency)
  // For a 16MHz clock and prescaler of 8, frequency = 16MHz / (8 * (ICR1 + 1))
  // To get approx. 500Hz: 16,000,000 / (8 * (3999 + 1)) = 500Hz
  ICR1 = 3999; 
  // Set initial duty cycle (0-ICR1)
  OCR1A = ICR1 / 2; // 50% duty cycle initially
}

void loop() {
  if (Serial.available()) {
    char cmd = Serial.read();  
    switch (cmd) {
      case '?':
        Serial.println("------------------------------");
        Serial.println("?: Help menu");
        Serial.println("p/P: decrease/increase PWM duty cycle");
        Serial.println("------------------------------");
        break;
      case 'p':
        if (duty >= DUTY_INC) {
          duty -= DUTY_INC;
          OCR1A = duty;
          Serial.print("The duty cycle is ");
          Serial.print(duty);
          sprintf(buff,"/%d",ICR1);
          Serial.println(buff);
        } else {
          Serial.println("Duty cycle at minimum");
        }
        break;
      case 'P':
        if (duty <= ICR1 - DUTY_INC) {
          duty += DUTY_INC;
          OCR1A = duty;
          Serial.print("The duty cycle is ");
          Serial.print(duty);
          sprintf(buff,"/%d",ICR1);
          Serial.println(buff);
        } else {
          Serial.println("Duty cycle at maximum");
        }
        break;
      case 'z':
        for (uint8_t i = 0; i < 40; i++) Serial.println();
        break;
      default:
        Serial.print("Unknown key ");
        Serial.println(cmd);
        break;
    }
    Serial.print("> "); 
  }
}