#include <Arduino.h>

hw_timer_t *timer = NULL;

volatile int currentLED = 0;
const int ledPins[] = {15,2,4,18,19,21,22,23};

bool forward = true;

void IRAM_ATTR onTimer() {
  for (int i = 0; i < 8; i++) {
    digitalWrite(ledPins[i], LOW);
  }

  digitalWrite(ledPins[currentLED], HIGH);

  if (forward) {
    currentLED += 2;
    if (currentLED >= 7) {
      currentLED = 7;
      forward = false;  
    }
  } else {
    currentLED -= 2;
    if (currentLED <= 0) {
      currentLED = 0;
      forward = true;
    }
  }
}
void setup() {
  for (int i = 0; i < 8; i++) {
    pinMode(ledPins[i], OUTPUT);
  }

  timer = timerBegin(1e6);
  timerAttachInterrupt(timer, &onTimer);
  timerAlarm(timer, 1e6, true, 0);
}

void loop() {
}