int main()
{
  DDRB = 0x37; //0011 0111
  while(true)
  {
    PORTB = 0x20; // 0010 0000
    delay_ms(1000);
    for (byte i = 4; i > 0; i--)
    {
      if (i == 2)
        PORTB >>= 2; // 0000 0100
      else
        PORTB >>= 1; // 0001 1011
        delay_ms(1000);
    }
    PORTB = 0x37;
    delay_ms(1000);
    PORTB = 0;
    delay_ms(2000);
  }
  return 0;
}

void delay_ms(unsigned int time_ms)
{
  while(time_ms--)
  {
    // Base value
    TCNT1 = 0;

    // Set WGM12 to 1 enables CTC mode
    // and counter value in OCR1A
    // CS11 & CS10 gives Prescaler = 64
    // clk_IO = 16MHz
    TCCR1A = 0;
    TCCR1B = (1 << WGM12) | (1 << CS11) | (1 << CS10);
    // T_latency = 1ms
    // OCR1A = clk_IO / Prescaler / (1/T_latency) - 1
    OCR1A = 249;
    // Check if interrupt flag is set after
    // value of TCNT1 the same as OCF1A
    while (!(TIFR1 & (1 << OCF1A)));
    TIFR1 |= (1 << OCF1A);
  }
}