#define GPIO2 2
#define GPIO25 25
unsigned long last_time_GPIO2 = 0;
unsigned long last_time_GPIO25 = 0;
int counter = 0;

void setup(){
  Serial.begin(115200);
  pinMode(GPIO2, OUTPUT);
  pinMode(GPIO25, OUTPUT);
}

void loop(){
  if(millis() - last_time_GPIO2 >= 500){
    digitalWrite(GPIO2, !digitalRead(GPIO2));
    last_time_GPIO2 = millis();
    Serial.println("GPIO2 on off");
  }
}