int pins[] = {2, 3, 4, 5, 6, 7, 8, 9};
int timer = 75;
void setup() {
  // Release 3/4 from JTAG to allow GPIO use while keeping SWD active
  
  for (int i = 0; i < 8; i++) {
    pinMode(pins[i], OUTPUT);
  }
}
void loop() {
  for (int i = 0; i < 8; i++) {
    digitalWrite(pins[i], HIGH);
    delay(timer);
    digitalWrite(pins[i], LOW);
  }
  for (int i = 6; i >= 1; i--) {
    digitalWrite(pins[i], HIGH);
    delay(timer);
    digitalWrite(pins[i], LOW);
  }
}