// Timer with an ISR example
// Author: Nick Gammon
// Date: 13th January 2012
// Modified: 19 October 2014

//#include <digitalWriteFast.h>

const byte FIRE_SENSOR = 2;  // note this is interrupt 0
const byte SPARKPLUG = 9;

void activateInterrupt0 ()
  {
  EICRA &= ~(bit(ISC00) | bit (ISC01));  // clear existing flags
  EICRA |=  bit (ISC01);    // set wanted flags (falling level interrupt)
  EIFR   =  bit (INTF0);    // clear flag for interrupt 0
  EIMSK |=  bit (INT0);     // enable it
  }  // end of activateInterrupt0

void deactivateInterrupt0 ()
  {
  EIMSK &= ~bit (INT0);     // disable it
  }  // end of deactivateInterrupt0

ISR (INT0_vect)
  {

   
    digitalWrite (SPARKPLUG, HIGH);

  
  
  } // end of ISR (INT0_vect)
  

void setup() 
  {
  
  //TCCR1A = 0;  // normal mode
  //TCCR1B = 0;  // stop timer
  //TIMSK1 = 0;  // cancel timer interrupt

  pinMode (SPARKPLUG, OUTPUT);
  pinMode (FIRE_SENSOR, INPUT_PULLUP);
  
  activateInterrupt0 ();
  }  // end of setup

void loop() 
  { 
  // read sensors, compute time to fire spark



  digitalWrite (SPARKPLUG, LOW);
  
  
  }  // end of loop