#include "Arduino.h"
#include <avr/interrupt.h>

//------------------------------------------------------------------------------
// 16-bit Timer/Counter 1 Overflow Interrupt alle 4ms (16Mhz/2^16)
//------------------------------------------------------------------------------
ISR( TIMER1_OVF_vect )
{
 volatile byte r2 = 0xFF, r5 = 0; //Werden in Timer1 Compare A ISR und Main verwendet
 static uint8_t r1, r3 = 0xFF, r4 = 0xFF; //Fuer Timer1 Compare A ISR reserviert
 
 // r1 = interrupt Arbeitsregister

 // r2 = key_state ;Entprellter Tasterzustand invertiert
 // r3 = key_ct0   ;2-Bit Abwaertszaehler Bit0
 // r4 = key_ct1   ;2-Bit Abwaertszaehler Bit1
 // r5 = key_press ;Taster entprellt gedrueckt gespeichert
  asm volatile
      (
        "in  r1,0x0C ;PINE      \n\t"
        "com r1      ;low activ \n\t"
        "eor r1,r2   ;          \n\t"
        "and r3,r1   ;          \n\t"
        "com r3      ;          \n\t"
        "and r4,r1   ;          \n\t"
        "eor r4,r3   ;          \n\t"
        "and r1,r3   ;          \n\t"
        "and r1,r4   ;          \n\t"
        "eor r2,r1   ;          \n\t"
        "and r1,r2   ;          \n\t"
        "or  r5,r1   ;          \n\t"
      );  
} // Ende ISR ( TIMER1_COMPA_vect )

// Arduino IOs
#define LED_GN  6
#define LED_GE  7
#define LED_RT  8
//------------------------------------------------------------------------------
// SETUP
//------------------------------------------------------------------------------
void setup() {
 // Timer 1, Waveform Generation Mode 0 => Normal Mode  Ueberlauf nach 4,096ms
 // TCCR1A  = 0;                        
 // TCCR1B  = 0; 
  TIFR1  |= 1<< TOV1;     //Timer1 Overflow Flag ruecksetzen falls gesetzt
  TIMSK1 |= 1<< TOIE1;    //Timer1 Overflow Interrupt Enable
  TCCR1B &= 0b11111000|0b001<< CS10; //Timer1 ohne Vorteiler starten

  pinMode(LED_RT, OUTPUT);
  pinMode(LED_GE, OUTPUT);
  pinMode(LED_GN, OUTPUT);
}

//------------------------------------------------------------------------------
// LOOP
//------------------------------------------------------------------------------
void loop() {
   
}