// https://wokwi.com/projects/448153462893255681
// https://forum.arduino.cc/t/atmega328pb-wake-with-button-interrupt/1414866

const byte ledYellow = 10;
const byte ledRed    = 8;  
const byte ledGreen  = 9;
const byte ledBlue   = 11;

void setup() {
  Serial.begin(9600);
  Serial.println("\nWake up!\n");
}

void loop() {

  rotate(); // take one step in the rotate pattern if it is time

// this clogs the serial buffer and reduces the speed
// but shows the free running nature of the loop
//  static int counter;
//  Serial.print(counter); counter++;
//  Serial.println(" loop.");
}

void rotate() {
// sequence of pins
  const byte ledPins[] = {
    ledYellow, ledRed, ledGreen, ledBlue,
  };

// compiler alculates lenth of the sequence
  const byte lenth = sizeof ledPins / sizeof *ledPins;


  static byte pc;
  static unsigned long lastTime;

  unsigned long now = millis();

  if (now - lastTime < 333) return;

  digitalWrite(ledPins[pc], LOW);
  pc++; if (pc >= lenth) pc = 0;
  digitalWrite(ledPins[pc], HIGH); 

  lastTime = now;
}