#include <stdint.h>
#include <avr/io.h>
#include <avr/interrupt.h>
 
#ifndef F_CPU
#define F_CPU           1000000                   // processor clock frequency
#endif
 
#define KEY_PORT        PORTB
#define KEY_PIN         PINB

//-----------------brauche ich nicht ??-------------------------------------------
#define KEY0            0
#define KEY1            1
#define KEY2            2
#define ALL_KEYS        (1<<KEY0 | 1<<KEY1 | 1<<KEY2)
 
#define REPEAT_MASK     (1<<KEY1 | 1<<KEY2)       // repeat: key1, key2
#define REPEAT_START    50                        // after 500ms
#define REPEAT_NEXT     20                        // every 200ms
//---------------------------------------------------------------------------------
 
#define LED_DDR         DDRA
#define LED_PORT        PORTA
#define LED0            0
#define LED1            1
#define LED2            2
 
uint8_t key_state;                                // debounced and inverted key state:
                                                  // bit = 1: key pressed
uint8_t key_press;                                // key press detect
 
uint8_t key_rpt;                                  // key long press and repeat
 
 
ISR( TIMER0_OVF_vect )                            // every 10ms
{
  static uint8_t ct0, ct1, rpt;
  uint8_t i;
 
  TCNT0 = (uint8_t)(int16_t)-(F_CPU / 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

//----------------------------brauche ich nicht, oder ?-----------------------------------
 
  if( (key_state & REPEAT_MASK) == 0 )            // check repeat function
     rpt = REPEAT_START;                          // start delay
  if( --rpt == 0 ){
    rpt = REPEAT_NEXT;                            // repeat delay
    key_rpt |= key_state & REPEAT_MASK;
  }
//-----------------------------------???--------------------------------------------------
}
 
///////////////////////////////////////////////////////////////////
//
// check if a key has been pressed. Each pressed key is reported
// only once
//


uint8_t get_key_press( uint8_t 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 )
{
  DDRB = 0x00;
  PORTB = 0xFF;
 
  TCCR0 = (1<<CS02)|(1<<CS00);			// divide by 1024
  TIMSK = 1<<TOIE0;				// enable timer interrupt
 
  LED_PORT = 0xFF;
  LED_DDR = 0xFF;
 
  sei();
 
  for(;;) {                                       // main loop
                                                  // single press
 
    if( get_key_press( 1<<KEY0 ))
      LED_PORT ^= 1<<LED0;

// könnte ich auch schreiben .. anstatt KEY0 --> z.B PB0 oder PB1 oder PD5 ????

    
                                                 
  }
}