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

// This sketch reads Nano pin 12 and mirrors it onto pin 13.
// I'm not sure even this will be fast enough to mirror WS2812 protocol.

// This function will be called each time PB4 changes level
ISR(PCINT0_vect) {
  if (PINB & (1<<PINB4))    // if PINB4 is high
    PORTB |= (1<<PORTB5);   // set PINB5 high 
  else
    PORTB &= ~(1<<PORTB5);  // set PINB5 low
}

int main(void) {
  cli();                    // disable interrupts during setup

  DDRB |= (1 << PB5);       // set PB5 as output pin (nano pin 13)
  DDRB &= ~(1 << DDB4);     // set PB4 as an input pin (nano pin 12)

  PCMSK0 |= (1 << PCINT4);  // set pin-change mask for interrupt 4
  PCICR |= (1 << PCIE0);    // enable pin-change interrupt

  sei();                    // enable interrupts

  while (1) {
  }
}