// ATtiny85 external interrupts exemple

#define LED_PIN 1  // -----> PB1
#define INTERRUPT_PIN 2 // INT0 -> PB2

volatile byte i = 0;
void setup() 
{
  GIMSK |= (1 << INT0); // enable external interrupt
  MCUCR |= (1 << ISC00); // Falling mode sense
sei();
 // pinMode(INTERRUPT_PIN, INPUT_PULLUP);
  pinMode(LED_PIN, OUTPUT);
}

void loop()
{
  digitalWrite(LED_PIN, i);
}

ISR(INT0_vect)
{
  i = digitalRead(INTERRUPT_PIN);
}