/*
  Forum: https://forum.arduino.cc/t/esp32-timer-reloading/1364408
  Wokwi: https://wokwi.com/projects/425693519758915585

  References: [1] https://espressif-docs.readthedocs-hosted.com/projects/arduino-esp32/en/latest/api/timer.html
              [2] https://docs.espressif.com/projects/arduino-esp32/en/latest/migration_guides/2.x_to_3.0.html#timer

  2025/03/17
  ec2021

  Due to an example in reference [1] it is allowed to use digitalRead/write in the ISR outside of the critical part
  As the timer did not stop (as expected from the documentation) it is freed and newly created in the routines

*/


#include <Arduino.h>
constexpr byte BTN_START_ALARM  {12};
constexpr byte LED_PIN {14};
volatile byte _ledState = LOW;

hw_timer_t * timer = NULL;
portMUX_TYPE timerMux = portMUX_INITIALIZER_UNLOCKED;
boolean detectLowSignal = false;

void ARDUINO_ISR_ATTR onTimer() {
  setLed(LOW);
}

void setup() {
  Serial.begin(115200);
  pinMode(BTN_START_ALARM, INPUT_PULLUP);
  pinMode(LED_PIN, OUTPUT);
}


void loop() {
  byte inputState = digitalRead(BTN_START_ALARM);
  if (inputState == LOW && !ledState()) {
    setLed(HIGH);
    detectLowSignal = true;
    Serial.println("Led ON");
    startTimer();
  }
  if (detectLowSignal && !ledState()) {
    stopTimer();
    Serial.println("Led OFF");
    detectLowSignal = false;
  }
}

void startTimer(){
    timer = timerBegin(1000000);
    timerAttachInterrupt(timer, &onTimer);
    timerAlarm(timer, 6000000, false, 0);
    Serial.println("Timer started");
}

void stopTimer(){
  if (timer){
    timerEnd(timer);
    Serial.println("Timer stopped");
  }
}

void setLed(byte state){
  digitalWrite(LED_PIN, state);
  portENTER_CRITICAL_ISR(&timerMux);
  _ledState = state;
  portEXIT_CRITICAL_ISR(&timerMux);
}

byte ledState(){
  portENTER_CRITICAL_ISR(&timerMux);
  byte state = _ledState;
  portEXIT_CRITICAL_ISR(&timerMux);
  return state;
}