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Arduino memory usage


I am doing some tests to try to understand how C++ impacts available memory in the Arduino.  I am profiling some code I have written and trying

to understand the impact of allocating objects on the stack with the new command (which traditionally uses malloc or one of its derivations under

the hood - is that true with the gcc compiler?).  As I understand it, the Arduino has

32k program memory - the program size it shows in the UI for the Arduino - Binary sketch size: 14,218 bytes (of a 32,256 byte maximum)2k sram -

which shares the stack and any program memory allocated ( ie int t = 20 ; t is allocated here).
1k eeprom - can put storage here -- reading and writing will be slow to this memory -- not important to this testing since I want fast access.

I found the memoryTest() code somewhere online.  Offhand, this seems it should work and should be accurate, but not sure.  I know this would work

with a PC, but not sure with an Arduino.

// this function will return the number of bytes currently free in RAM
int memoryTest() {
  int byteCounter = 0; // initialize a counter
  byte *byteArray; // create a pointer to a byte array
  // More on pointers here: http://en.wikipedia.org/wiki/Pointer#C_pointers

  // use the malloc function to repeatedly attempt allocating a certain number of bytes to memory
  // More on malloc here: http://en.wikipedia.org/wiki/Malloc
  while ( (byteArray = (byte*) malloc (byteCounter * sizeof(byte))) != NULL ) {
    byteCounter++; // if allocation was successful, then up the count for the next try
    free(byteArray); // free memory after allocating it
  free(byteArray); // also free memory after the function finishes
  return byteCounter; // send back the highest number of bytes successfully allocated

char * array = char(1024);

void setup()
  Serial.begin(9600) ;
void loop()


If I run this, I get 638 back from the memoryTest() call.  If I remove the array allocation, I get 1278 as available sram. I have tried a number

of different allocations using the C++ new command, and no matter what allocations I use, I either get back 638 or 1278 for available sram.  I am

sure it allocates memory in large chunks but was hoping there was an expert on how the gcc compiler manages memory.

char * array = char(2048);

definitely fails returns null as you would expect. 

char * array = char(1024);

will succeed but then the memoryTest() will return 1278 which would seem inaccurate.  Something weird going on here.  Any ideas?



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I found this "freeRAM()" function a while ago maybe it can help?


Will have to compare this versus what I am using and see if they agree.  Great to have in the developer's quiver as it were.  Thanks!