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;
  const char in  = 3;
  const char out = 0;
  const char pwr = 1;
  char *timer = &TIMSK;
*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?

1 Answer 1


Just as a complement to Delta_G's answer:

  1. 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

    A const pointer for &TIMSK0 is fine though.

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

    #ifdef __AVR_ATtiny45__
    #if defined(__AVR_ATtiny45__)
    #if __AVR_ATtiny45__

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

    #if __AVR_ATtiny25__ || __AVR_ATtiny45__ || __AVR_ATtiny85__

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