#include <avr/io.h>
#include <util/delay.h>
#include <avr/interrupt.h>

unsigned volatile char inc;

#define F_CPU 1000000UL
#define DELAY_MAX 2900
#define DELAY_MIN 400

ISR (INT0_vect){
    inc = 0;//decrease delay
}

ISR (INT1_vect){
    inc = 1;//increase delay
}

int main(void)
{
    /* Replace with your application code */

    unsigned char led_on = 0b00100000;
    unsigned char led_off = 0b00000000;
    unsigned int delay = DELAY_MIN;

    DDRB = 0xFF;
    PORTB = ~led_on;
    DDRD = 0x00;
    PORTD = 0xFF;

    EIMSK=0b00000011;
    EICRA=0b00001010;

    sei();

    while (1)
    {
        PORTB = ~led_off;
        switch(delay){
            case 400:
              _delay_ms(400);
            case 900:
              _delay_ms(900);
            case 1400:
              _delay_ms(1400);
            case 1900:
              _delay_ms(1900);
            case 2400:
              _delay_ms(2400);
            case 2900:
              _delay_ms(2900);
            default:
            _delay_ms(400);
        }
        PORTB = ~led_on;

        if(inc == 1) {
            if(delay >= DELAY_MIN && delay < DELAY_MAX) {
                delay += 500;
            }
        }
        else{
            if(delay > DELAY_MIN && delay <= DELAY_MAX) {
                delay -= 500;
            }
        }
    }
}