/*
 Controlling a servo position using a potentiometer (variable resistor)
 by Michal Rinott <http://people.interaction-ivrea.it/m.rinott>

 modified on 8 Nov 2013
 by Scott Fitzgerald
 http://www.arduino.cc/en/Tutorial/Knob
*/


/* Example code with timer intyerrutp that will create an interruption each 
   500ms using timer1 and prescalar of 256.
   Calculations (for 500ms): 
   System clock 16 Mhz and Prescalar 256;
   Timer 1 speed = 16Mhz/256 = 62.5 Khz    
   Pulse time = 1/62.5 Khz =  16us  
   Count up to = 500ms / 16us = 31250 (so this is the value the OCR register should have)
  */ 



void setupTimer()
{
  cli();                      //stop interrupts for till we make the settings
  /*1. First we reset the control register to amke sure we start with everything disabled.*/
  TCCR1A = 0;                 // Reset entire TCCR1A to 0 
  TCCR1B = 0;                 // Reset entire TCCR1B to 0
 
  /*2. We set the prescalar to the desired value by changing the CS10 CS12 and CS12 bits. */  
  TCCR1B |= B00000100;        //Set CS12 to 1 so we get prescalar 256  
  
  /*3. We enable compare match mode on register A*/
  TIMSK1 |= B00000010;        //Set OCIE1A to 1 so we enable compare match A 
  
  /*4. Set the value of register A to 31250*/
  OCR1A = 31250;             //Finally we set compare register A to this value  
  sei();           
}



bool isrState;
bool ledState;

void setup() 
{

  setupTimer();

  isrState = false;
  ledState = false;
  digitalWrite(13, LOW);
}

void loop() 
{

  if(isrState)
  {
    if(ledState)
    {
      digitalWrite(13, LOW);
      ledState = false;
    }
    else
    {
      digitalWrite(13, HIGH);
      ledState = true;
    }
    
    isrState = false;
  }

}

ISR(TIMER1_COMPA_vect)
{
  TCNT1  = 0;                  //First, set the timer back to 0 so it resets for next interrupt
  isrState = true;
}