/*
  TODO:
  https://www.youtube.com/watch?v=qsflCf6ahXU
  deal with max or min rpm limits
  detect when there's no interrupts happening (0 rpm)
  use float rpm for improved resolution?
*/

TaskHandle_t Task1;

const byte   pulsesPerRevolution = 1;
const unsigned long usPerRevolution = 60000000 / pulsesPerRevolution;
const unsigned int printMs = 250;

volatile unsigned long us, prevPulseUs, pulseUs;
unsigned long prevPulseUsCopy, pulseUsCopy, prevMs, now, pulsePeriod, rpm;

void IRAM_ATTR isr() {
  us = micros();
  if ((us - pulseUs) > 100) {  // debounce interval, also determines max rpm
    prevPulseUs = pulseUs;
    pulseUs = us;
  }
}

void setup() {
  Serial.begin(115200);
  pinMode(5, OUTPUT);
  attachInterrupt(digitalPinToInterrupt(19), isr, RISING);
  xTaskCreatePinnedToCore(
    Task1code,   /* Task function. */
    "Task1",     /* name of task. */
    10000,       /* Stack size of task */
    NULL,        /* parameter of the task */
    1,           /* priority of the task */
    &Task1,      /* Task handle to keep track of created task */
    0);          /* pin task to core 0 */
  delay(500);
}

void loop() {
  delay(5);
}

//Task1code: pwmOut follows pwmIn
void Task1code( void * pvParameters ) {
  for (;;) {

    bool timeOut;
    now = millis();
    if ((now - prevMs) >= printMs) {
      prevMs = now;
      timeOut = true;
    }
    else timeOut = false;

    if (timeOut) {  // 4 Hz update frequency
      noInterrupts();
      prevPulseUsCopy = prevPulseUs;
      pulseUsCopy = pulseUs;
      interrupts();
      pulsePeriod = pulseUsCopy - prevPulseUsCopy;
      if (pulsePeriod > 1000000) rpm = 0;  // Show 0 rpm when input < 1 Hz (60 rpm)
      else if (pulsePeriod < 1000) rpm = 60000; // show 60000 rpm max when input > 1kHz
      else rpm = usPerRevolution / pulsePeriod;
      Serial.println(rpm);
    }
  }
}