Question

How the processor (Atmega328) manages subroutine calls and possibly recursive calls ??

Answer 1

Burning the Bootloader

Upload the ArduinoISP sketch onto your Arduino board. ...
Wire up the Arduino board and microcontroller as shown in the diagram to the right.
Select "Arduino Duemilanove or Nano w/ ATmega328" from the Tools > Board menu. ...
Select "Arduino as ISP" from Tools > Programmer.
Run Tools > Burn Bootloader.
Since the call stack is organized as a stack, the caller pushes the return address onto the stack, and the called subroutine, when it finishes, pulls or pops the return address off the call stack and transfers control to that address.

CALL and RETURN instructions. The CALL instruction interrupts the flow of a program by passing control to an internal or external subroutine. ... An external subroutine is another program. The RETURN instruction returns control from a subroutine back to the calling program and optionally returns a value

A routine or subroutine, also referred to as a function, procedure, and subprogram, is code that may be called and executed anywhere in a program. For example, a routine may be used to save a file or display the time. ... Below is a basic example of a Perl subroutine.