/*
  Forum: https://forum.arduino.cc/t/calculating-periodic-time-using-micros-on-arduino-nano/1336853
  Wokwi: https://wokwi.com/projects/418610438465724417

  2024/12/29
  ec2021

*/


// Added to create a digital input for the ISR
// The togglePin switches its state (LOW-> HIGH-> LOW-> ...) every timer1 interrupt.
// As the ISR reacts on a falling edge only
// the measured period equals 2 x timerInterval
#include <TimerOne.h>;
const byte togglePin {3};
const unsigned long timerInterval = 500; //micro seconds !!!

#define INPUT_PIN_1 2

volatile unsigned long PT = 0;

// No need for volatile as FREQ and RPM_Reading are not used in the ISR
float FREQ = 0;
float RPM_Reading = 0;

// Moved to ISR
// volatile unsigned long currentTime = 0;
// volatile unsigned long lastTime = 0;

void setup()
{
  // TimerOne
  Timer1.initialize(timerInterval);
  Timer1.attachInterrupt(toggle);
  pinMode(togglePin, OUTPUT);

  Serial.begin(115200);
  pinMode(INPUT_PIN_1, INPUT_PULLUP);
  attachInterrupt(digitalPinToInterrupt(INPUT_PIN_1), InterruptSR, FALLING);
}

void loop()
{
  // Copy PT to the variable copyPT which is "outside" of the ISR
  noInterrupts();
  unsigned long copyPT = PT;
  interrupts();

  FREQ = 1000000.0 / copyPT;             // Calculate frequency in Hz
  RPM_Reading = FREQ * 60;           // Convert frequency to RPM
  // not ms but micro seconds
  //Serial.print("periodic time in ms: ");
  Serial.print("periodic time in µs: ");
  Serial.println(copyPT);
  Serial.print("frequency: ");
  Serial.println(FREQ);
  Serial.print("RPM: ");
  Serial.println(RPM_Reading);
}

void InterruptSR()
{
  static unsigned long lastTime = 0;
  unsigned long currentTime = micros();
  PT = currentTime - lastTime;
  lastTime = currentTime;
}


void toggle() {
  static byte state = LOW;
  digitalWrite(togglePin, state);
  state = !state;
}