#pragma GCC optimize "-Og"
#include "ArduinoTrace.h"

volatile byte dato;

void setup() {
  // put your setup code here, to run once:
  Serial.begin(9600);
  //PORTD=PORTD|(1<<PD4);           //board pin 4 pull-up resistor
  //asm volatile
  // (
  //   "lds r24,%1 \n"
  //   "ori r24,0x10 \n"
  //   "sts %1 ,r24"
  //   :"=m" (PORTD)
  //   :"m" (PORTD)
  // );
    asm volatile
    (
      "lds r24,%[aPORTD] \n"
      "ori r24,0x10 \n"
      "sts %[aPORTD],r24"
      :[aPORTD]"=m" (PORTD)
      :"0" (PORTD)
    );

  //DDRB=DDRB|(1<<PB0);             //led pin output
  asm volatile
  (
    "sbi	%0,0"
    :
    :"I" (_SFR_IO_ADDR(DDRB))
  );
}

void loop() {
  // put your main code here, to run repeatedly:
  //dato=PIND&0x10;                //aislar bit 4 de PIND
  asm volatile
  (
    "in  r24,%0 \n"
    "andi r24,0x10 \n" 
    "sts dato,r24"
    :
    :"I" (_SFR_IO_ADDR(PIND))
  );

  if(dato==0)                     //si pulsador oprimido (bit 4 de PIND en 0)   
  {
    //PORTB=PORTB|(1<<PB0);       //led on
    asm volatile
    (
      "sbi	%0, 0"
      :
      :"I" (_SFR_IO_ADDR(PORTB))
    );
  }
  else                            //sino:
  {
    //PORTB=PORTB&~(1<<PB0);      //led off
    asm volatile
    (
      "cbi	%0, 0"
      :
      :"I" (_SFR_IO_ADDR(PORTB))
    );
  }
}