LED mit wählbarer Frequenz blinken lassen (Pollin Board/ATmega644/WinAVR)

#include <avr/interrupt.h>

#include <avr/io.h>

#include <stdbool.h>

#define sbi(x,b) x |= (1 << (b))

#define cbi(x,b) x &= ~(1 << (b))

void delayMs( unsigned int ms )

{

  while( ms > 0 )

    {

    TCNT0 = 0;

    while( TCNT0 < 64 ){;}

    ms--;

    }

}

bool  pressed  = false;

int    freq  = 1000;

int main(void)

{

  // Disable watchdog

  WDTCSR &= ~(1<<WDE);

  //Init timer

  cbi(TCCR0B,CS00);

  cbi(TCCR0B,CS01);

  sbi(TCCR0B,CS02);

  //Init Interrupt

  PCICR   = (1 << PCIE3);

  PCMSK3  = (1 << PCINT28);

  PCMSK3 |= (1 << PCINT27);

  PCMSK3 |= (1 << PCINT26);

  sei();

  DDRD  = 0b01100000;

  PORTD = 0b00011100;

  while(1)

    {

    PORTD ^= 0b01000000;

    delayMs(freq);

    }

  while (1) {}

}

ISR(PCINT3_vect)

{

  PORTD ^= 0b00100000;

  pressed = !pressed;

  if (pressed)

    {

    if(PIND4)

      { freq = 1000; }

    else if(PIND3)

      { freq = 500; }

    else if(PIND2)

      { freq = 250; }

    }

}