#include <avr/io.h>
#include <avr/interrupt.h>
//#include <avr/signal.h> //zu alt


#ifndef OCR1A
#define OCR1A OCR1	// 2313 support
#endif

#ifndef WGM12
#define WGM12 CTC1	// 2313 support
#endif

#ifndef	PINC
#define	KEY_INPUT	PIND	// 2313
#else
#define KEY_INPUT	PINC	// Mega8
#endif
#define	LED_DIR		DDRB

//#define XTAL		16000000L	// nominal value
#define XTAL		16000000L	// after measuring deviation: 1.5s/d

#define DEBOUNCE	256L		// debounce clock (256Hz = 4msec)

#define uchar unsigned char
#define uint unsigned int

uchar prescaler;
uchar volatile second;			// count seconds



SIGNAL (SIG_OUTPUT_COMPARE1A)
{
/************************************************************************/
/*			Insert Key Debouncing Here			*/
/************************************************************************/

#if XTAL % DEBOUNCE
  OCR1A = XTAL / DEBOUNCE - 1;		// compare DEBOUNCE - 1 times
#endif
  if( --prescaler == 0 ){
    prescaler = (uchar)DEBOUNCE;
    second++;				// exact one second over
#if XTAL % DEBOUNCE			// handle remainder
    OCR1A = XTAL / DEBOUNCE + XTAL % DEBOUNCE - 1; // compare once per second
#endif
  }
}


int main( void )
{
  LED_DIR = 0xFF;
  DDRD  |= (1 << PD6);
  while ( KEY_INPUT & 1 );		// start with key 0 pressed

  TCCR1B = 1<<WGM12^1<<CS10;		// divide by 1
					// clear on compare
  OCR1A = XTAL / DEBOUNCE - 1;
  TCNT1 = 0;
  second = 0;
  prescaler = (uchar)DEBOUNCE;

  TIMSK = 1<<OCIE1A;
  sei();
  
  if(second >= 30)
		PORTD |= (1 << PD6);

	
  for(;;){
    if( second == 60 )
      second = 0;
    LED_DIR = second;			// display second (binary)
  }
}