void setup() {
  // put your setup code here, to run once:
  volatile byte a,b,c;

  Serial.begin(9600);

  Serial.println("Enviar dato serial para variable local b:");
  while(Serial.available()==0){}
  delay(50);
  //pasar los bytes recibidos a un entero
  b=Serial.parseInt(SKIP_NONE,'\n');

  Serial.println("Enviar dato serial para variable local c:");
  while(Serial.available()==0){}
  delay(50);
  //pasar los bytes recibidos a un entero
  c=Serial.parseInt(SKIP_NONE,'\n');

  //a en Y+3, b en Y+2, c en Y+1 
  //-------------pasar a assembly-----------
    //fooA(a,b,c);
    //c=c+a;
    asm(
      
    "ldd r22,Y+2  \n"  
    "ldd r23,Y+1  \n"  
    "movw r24,r28 \n"  
    "adiw r24,3   \n"  
    "call fooA    \n"     //llamado funcion
    "ldd r24, Y+1 \n"  //r24 <-- c
    "ldd r25, Y+3 \n"  //r25 <-- a
    "add r24, r25 \n"  //r24 <-- c + a
    "std Y+1, r24 \n"  //c <-- c + a
    );
  //-----------------------------------------

  Serial.print("a = ");
  Serial.println(a);
  Serial.print("b = ");
  Serial.println(b);  
  Serial.print("c = ");
  Serial.println(c);  
}

void loop() {
  // put your main code here, to run repeatedly:

}

//-------------pasar a assembly----------------------
//byte fooA(volatile byte &q,volatile byte s,  volatile byte t)
//{
  //if(s<=t)
  //{
    //t=s+t;
  //}
  //else
  //{
    //t=s-t;
  //}
  //q=t;
//}
//----------------------------------------------------

asm("fooA: ");

asm(
  "push r28        \n"  //salvar Y del caller
  "push r29        \n"  //.................. 
  "push r0         \n"  //....................
  "push r0         \n"  //...................
  "push r0         \n"  //.................
  "push r0         \n"  //.................
  "in r28,  0x3d   \n"  // Y <-- SP
  "in r29,  0x3e   \n"  //.................
  "std Y+4, r23    \n"  //t <-- c
  "std Y+3, r22    \n"  //s <-- b
  "std Y+1, r24    \n"  //Y+1 
  "std Y+2, r25    \n"  //Y+2 
  "ldd r22, Y+3    \n"  //r22 <-- s
  "ldd r23, Y+4    \n"  //r23 <-- t
  "cp r23, r22    \n"  //s - t
  "brlo Q10        \n"  //brlo a Q10(else) si s >t
  "ldd r22, Y+3    \n"  //r22 <-- s
  "ldd r23, Y+4    \n"  //r23 <-- t
  "add r23 , r22    \n"  //r23 <-- s + t
  "std Y+4, r23    \n"  //t <-- s + t
  "rjmp Q20        \n"  //saltar el else
  "Q10:            \n"
  "ldd r22, Y+3    \n"  //r22 <-- s
  "ldd r23, Y+4    \n"  //r23 <-- t
  "sub r22, r23    \n"  //r22 <-- s -t
  "std Y+4, r22    \n"  //t <-- s - t
  "Q20:            \n"
  "ldd r24,Y+1     \n"  //r24 <-- low byte a
  "ldd r25,Y+2     \n"  //r25 <-- high byte a
  "movw r30,r24    \n"  //Z <-- a
  "ldd r18, Y+4    \n"  //r18 <-- t
  "st Z, r18       \n"  //a <-- t
  "pop r0          \n"  //se sacan los bytes de a
  "pop r0          \n"  //.......................
  "pop r0          \n"  //se saca s
  "pop r0          \n"  //se saca t
  "pop r29         \n"  //restauramos Y del caller
  "pop r28         \n"  //......................
  "ret             \n"  //PC <-- direccion de retorno al caller
  );