/* created by Bertrand VANDEPORTAELE */
#include <SPI.h>
#include <util/atomic.h>
const int ledPin=13; //broche 13=PB5   
#define XOR ^
 #define HEAT_BEAT_DIVIDER_MAX  129
 
 /*
periode  HEAT_BEAT_DIVIDER_MAX  
 520us     1
1042us   2
 1560us       3
 2080us   4
4160us  8
 20300us    39
 20850us    40
1045ms 2000
 1/15seconde ->  130
 */
 /////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
unsigned int heart_beat_divider = 0 ;
#define PRESCALER_INDEX 3
#define TIMER_PERIOD 8000 
// TIMER ISR VECTOR and configuration
unsigned char isr_modulo_count, global_isr_modulo = 0 ;
ISR(TIMER2_COMPA_vect){
   //transmit interrupt
     heart_beat_divider = heart_beat_divider + 1 ;
      if(heart_beat_divider >= HEAT_BEAT_DIVIDER_MAX){
         PORTB ^= 0x01 <<5 ; //bit 5 du port B
         heart_beat_divider = 0;
      }
}
/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
void setupTimer2(unsigned char prescaler, unsigned int period){
  TCCR2A = 0;// set entire TCCR2A register to 0
  TCCR2B = 0;// same for TCCR2B
  TCNT2  = 0;//initialize counter value to 0
  OCR2A = period;// = (16*10^6) / (8000*8) - 1 (must be <256)
  // turn on CTC mode
  TCCR2A |= (1 << WGM21);
 
  switch(prescaler){
    case 0 :
      // Set CS20 bit for no prescaler
      TCCR2B |= (1 << CS20);
    case 1 :
      // Set CS21 bit for 8 prescaler
      TCCR2B |= (1 << CS21);
    case 2 :
      // Set CS21 bit for 64 prescaler
      TCCR2B |= (1 << CS21) | (1 << CS20);
      break ;   
    case 3 :
      // Set CS21 bit for 128 prescaler
      TCCR2B |= (1 << CS22) ;
      break ; 
    case 4 :
      // Set CS21 bit for 256 prescaler
      TCCR2B |= (1 << CS22) | (1 << CS21);
      break ; 
     case 5 :
      // Set CS21 bit for 1024 prescaler
      TCCR2B |= (1 << CS22) | (1 << CS21) | (1 << CS20);
      break ;  
    default :
      TCCR2B |= (1 << CS20);
      break ;
 
  }
  // enable timer compare interrupt
  TIMSK2 |= (1 << OCIE2A); 
}  
/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
void setup() {
   // start serial port at 9600 bps:
  Serial.begin(115200);      
  pinMode(ledPin, OUTPUT);   
  cli();//stop interrupts
  setupTimer2(PRESCALER_INDEX, TIMER_PERIOD); // setup interrupt with prescaler (see datasheet for prescaler value, and reload value)
  sei();//allow interrupts
}
/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
void loop()
{
}