int main(void)
{	
	CLKPR = (1<<CLKPCE);        			// set Clock Prescaler Change Enable
    CLKPR = (1<<CLKPS0);				// set prescaler = 2, Inter RC 8Mhz / 2 = 4Mhz, max value for 1.8V types
	PCMSK0 |= (1<<PCINT2);				// PCI 2 on, this is PB2, reed contact wheel
	EIMSK |= (1<<PCIE0);				// Pin Change INT0 on
	ACSR |= (1<< ACD);				// Turn off analog comparator for power reduction
	PRR=0xFF;					// Reduce power of everything
	OCR2A=preload;
    cli();						// disabel global interrupt
    ASSR = (1<<AS2);					// select asynchronous operation of Timer2
    TCNT2 = 0;	
							// clear TCNT2A
    TCCR2A |= (1<<CS21) | (1<<WGM21);		// select precaler: 32.768 kHz / 8 = 1/64 sec between each CTC
	
	while((ASSR & 0x01) | (ASSR & 0x04));	// wait for TCN2UB and TCR2UB to be cleared
    TIFR2 = 0xFF;           				// clear interrupt-flags
    TIMSK2|= (1<<OCIE2A);     				// enable Timer2 CTC interrupt
	
	DDRA = 0xFF;
	DDRB = 0xFF; 
	DDRC = 0xFF; 
	DDRD = 0xFF;
	DDRE = 0xF8; 							//All Ports OUTPUTS except Wheel (PE2), PE0 and PE1
	DDRF = 0xEF;							//Port F4 input for external power sensing
	DDRG = 0xFF;
   
	max_veloc=0;
	power=1;
	sei();									//Enable all interrupts
	set_sleep_mode(SLEEP_MODE_PWR_SAVE);
    while(1)                    
    { 
	 unsigned long tmp;
	 sleep_mode();
	 if (new_round)
	 {
		new_round=0;
		{
		   time = tmp_rev*64+curr_TC-oldTC;
		   loc_tmp= 2160;
		   loc_tmp= 72*loc_tmp;
		   loc_tmp/=time;
			veloc=(loc_tmp+2)/5;	//km per hour, rounding included
		}
		oldTC=curr_TC;	//remember last Timer value
	 }
    }
	return (1);
}



ISR (SIG_PIN_CHANGE0)	
{
 if (!Reed_open)						//if contact closed
  {
	new_round=1;
	OCR2A=preload;
	while (ASSR&0x02) ;					//wait until OCR2UB reads 0, this ensures that TCNT2 reads correctly
	curr_TC = TCNT2;					//take snapshot of timer 2 status NOW!
	tmp_rev = revolution;
	if (TIFR2&0x02)						//in case Timer2 and PCI fire at the same time, PCI has priority
	 {
		tmp_rev++;
		revolution=0;
	 }
	else
		revolution=0;


ISR (TIMER2_COMP_vect)	//fires about every 15.6ms, 64Hz, takes maximum 400µs to complete @4MHz CPU clock	
{	

	revolution++;
	LCD Anzeige steuern...;
}