#define ITRG 2
hw_timer_t *tmrcfg_mS = NULL;
unsigned long tmNow, tmPrev, tmDiff;
unsigned char l33, l66, l100, l250;
unsigned short RPM;

void IRAM_ATTR triggerISR(){
  tmNow = micros();
  tmDiff = tmNow - tmPrev;
  if(tmPrev > 0){
    RPM = (60000000 / tmDiff);
  }
  tmPrev = tmNow;
} 

void IRAM_ATTR msISR()
{
  l33++;
  l66++;
  l100++;
  l250++;
  if(l33 == 33){l33 = 0;}
  if(l66 == 66){l66 = 0;}
  if(l100 == 100){l100 = 0;}
  if(l250 == 250){
    l250 = 0;
    digitalWrite(33, !digitalRead(33));
    //Serial.print("RPM:  "); Serial.println(RPM);
  }
}

void setup() {
  // put your setup code here, to run once:
  pinMode(33,OUTPUT);
  pinMode(ITRG, INPUT_PULLUP);
  attachInterrupt(ITRG, &triggerISR, FALLING);
  tmrcfg_mS = timerBegin(0, 80, true);
  timerAttachInterrupt(tmrcfg_mS, &msISR, true);
  timerAlarmWrite(tmrcfg_mS, 1000, true);
  timerAlarmEnable(tmrcfg_mS);
  //timerAlarm(tmrcfg_mS, 1000000, true, 0);
  Serial.begin(115200);
  //Serial.println("Hello, ESP32!");
  digitalWrite(33,0);
  Serial.println(timerGetFrequency(tmrcfg_mS));
}

void loop() {
  // put your main code here, to run repeatedly:
  delay(10);
}