I use this Library to measure my free RAM on a Mega in runtime. But this Library does not work on the Due.


As mentioned by Mikael Patel in a comment, the library from Arduino-MemoryFree should do it. A minimal sketch that seems to work on the Due:

extern "C" char* sbrk(int incr);

int freeMemory() {
  char top;
  return &top - reinterpret_cast<char*>(sbrk(0));

void setup ()
  Serial.begin (115200);
  Serial.println ();
  Serial.print ("Free memory is: ");
  Serial.println (freeMemory ());
}  // end of setup

void loop () { }

I'm not totally convinced that this gives the correct figure. The figure returned by the library above for my Uno was too high (2297 bytes).

  • It seems to work fine after a call to malloc(), which is needed to initialize __brkval. I would return &top - ( __brkval ? __brkval : &__heap_start); in order to have something that works also when not using malloc(). – Edgar Bonet Oct 25 '16 at 9:34
  • I thought it might be something like that. After all, not everyone uses malloc. – Nick Gammon Oct 25 '16 at 10:50

Try to use this method:

int freeRAM() {
  extern int __heap_start, *__brkval;
  int v;
  return (int) &v - (__brkval == 0 ? (int) &__heap_start : (int) __brkval);
  • 1
    The question was about a Due. When I tried your code on my Due I got -28 bytes of RAM, which is hard to believe. – Nick Gammon Oct 25 '16 at 8:36

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