How to specify a timer's name depending on the chip it will be compiled to?

Question

I need to enable a timer interrupt for a chip, and in the mean time, I am testing the code on Arduino Nano rather than (feed the chip, test the chip)++.

So as part of the code I have to TIMSK0 |= (1 << OCIE0A); which works great on the Arduino Nano, but has to be changed to TIMSK (without the 0) for the ATtiny45.

I was planning to go for something along the line of

#define NANO//Put // in front for the AtTiny45
#ifdef NANO
  const char in  = A0;
  const char out = 3;
  const char pwr = 10;
  char *timer = &TIMSK0;
#else
  const char in  = 3;
  const char out = 0;
  const char pwr = 1;
  char *timer = &TIMSK;
#endif
//...
*timer  |= (1 << OCIE0A);

So here are my three questions:

• Do #these commands take space on a chip?
• Is a pointer the way to go for this kind of things?
• Am, am I doing it right?

Answer 1

Just as a complement to Delta_G's answer:

2. The names TIMSK0, OCIE0A, etc. are already preprocessor macros so, for consistency, it makes sense to define your own preprocessor macros for them. I tend to be lazy and use one of the already defined names, like

   #ifdef TIMSK0  // support both ATtiny{25,45,85} and ATmega328P
   # define TIMSK TIMSK0
   #endif
   

   A const pointer for &TIMSK0 is fine though.

3. The macros identifying the MCU are defined to the value 1. Thus you have the choice between these three idioms:

   #ifdef __AVR_ATtiny45__
   ...
   #endif
   
   #if defined(__AVR_ATtiny45__)
   ...
   #endif
   
   #if __AVR_ATtiny45__
   ...
   #endif
   

   The third one is convenient when you want to address several MCU models with the same code:

   #if __AVR_ATtiny25__ || __AVR_ATtiny45__ || __AVR_ATtiny85__
   ...
   #endif