How to measure free RAM on an Arduino Due in Runtime?
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 &amp;top - reinterpret_cast&lt;char*&gt;(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).