void init_port();
void init_timer();

void setup() {
  volatile long i;
  int j=0;
  init_port();
  init_timer();
  Serial.begin(9600);
  while(1)
  {
    for(i=0; i<1000000; i++);
    Serial.println(j,DEC);
    j++;
  }
}

void init_timer(){

 volatile char *Timer1_TCCR1A = 0x80;
 volatile char *Timer1_TCCR1B = 0x81;
 volatile short *Timer1_TCNT1 = 0x84;
 volatile short *Timer1_OCR1A = 0x88;
 volatile char *Timer1_TIMSK1 = 0x6F;

  *Timer1_TCCR1A = 0;
  *Timer1_TCCR1B = 0;
  *Timer1_TCNT1  = 0;

  *Timer1_OCR1A  = 60000;            // compare match register 16MHz/256/2Hz  31250
  *Timer1_TCCR1B = 0x0C;             // CTC mode & 256 prescaler 
  *Timer1_TIMSK1 = 0x02;            // enable timer compare interrupt
}

void init_port()
{

  volatile char *portf_dir  = (volatile char *)0x30;
  *portf_dir = 0x01;
}

ISR(TIMER1_COMPA_vect)          // timer compare interrupt service routine
{
  volatile char *portf_data = (volatile char *)0x31; 
  *portf_data  ^= 0x01;
}

void loop() {
  // put your main code here, to run repeatedly:
}