/************************************************************************/
/*                                                                      */
/*                      Debouncing 8 Keys	        					*/
/*			Sampling 4 Times											*/
/*			With Repeat Function										*/
/*                                                                      */
/*              Author: Peter Dannegger                                 */
/*                      danni@specs.de                                  */
/*                                                                      */
/************************************************************************/

#include <io.h>
#include <interrupt.h>

typedef unsigned char	u8;
typedef signed short	s16;

#define	XTAL		8e6		// 8MHz

#define KEY_PIN		PIND
#define KEY0		0

#define LED_DDR		DDRB
#define LED_PORT	PORTB
#define LED0		0


u8 key_state;				// debounced and inverted key state:
					// bit = 1: key pressed
u8 key_press;				// key press detect


ISR (SIG_OVERFLOW0)			// every 10ms
{
  static u8 ct0, ct1;
  u8 i;

    TCNT0 = (u8)(s16)-(XTAL / 1024 * 10e-3 + 0.5);	// preload for 10ms

  i = key_state ^ ~KEY_PIN;		// key changed ?
  ct0 = ~( ct0 & i );			// reset or count ct0
  ct1 = ct0 ^ (ct1 & i);		// reset or count ct1
  i &= ct0 & ct1;			// count until roll over ?
  key_state ^= i;			// then toggle debounced state
  key_press |= key_state & i;		// 0->1: key press detect


}


u8 get_key_press( u8 key_mask )
{
  cli();					// read and clear atomic !
  key_mask &= key_press;                        // read key(s)
  key_press ^= key_mask;                        // clear key(s)
  sei();
  return key_mask;
}



int main( void )
{
  TCCR0 = 1<<CS02^1<<CS00;			// divide by 1024
  TIMSK = 1<<TOIE0;				// enable timer interrupt

  DDRD = 0xFF;					//Pull-Ups für Eingang
  LED_PORT = 0xFF;
  LED_DDR = 0xFF;
  sei();

  for(;;){					// main loop
			
    if( get_key_press( 1<<KEY0 ))
      LED_PORT ^= 1<<LED0;

  }
}