Memory info

Using Arduino Programming Questions
#1

Is there a function I can call to see how much memory is left in RAM?

#2

No.

But this might help a few people:

/*
  Free Memory detection
 From Arduino Cookbook
 Modified by WillR March 22, 2011
 Did I improve it or change it?
 Good Question!

 */

// external variables from build process

//String mystring[] = "testing";

//unsigned long myVal;

void setup() {

  Serial.begin(115200); 

} //end setup

void  loop()
{
  Serial.print("Free Memory:  ");
  Serial.print(memoryFree()); 
  Serial.println("  ");  
  delay(1000);

} //end loop



extern unsigned long __bss_end;
extern void *__brkval;

int memoryFree()
{
  //  long myValue;
  int freeValue;
  freeValue = 0;

  if ((unsigned long)__brkval == 0)
  { 
    freeValue = ((unsigned long)&freeValue) - ((unsigned long)&__bss_end);
    //       Serial.println("here and there");
  }
  else
  { 
    freeValue = ((unsigned long)&freeValue) - ((unsigned long)__brkval);
    //      Serial.println("here  2");
  }

  return freeValue;

}//end memoryFree()

It seems to give reasonable answers.

#3

You would also find this AVR-LIBC documentation interesting as it explains what is going on: http://avr-libc.nongnu.org/user-manual/malloc.html

This topic comes up from time to time. The last time I remember was this: http://arduino.cc/forum/index.php/topic,50924 But if you search around a bit you'll find others, including in the old forums.

#4

That looks pretty good. And throwing in malloc (100) into the loop gives this:

Free Memory:  1834  
Free Memory:  1732  
Free Memory:  1630  
Free Memory:  1528  
Free Memory:  1426  
Free Memory:  1324  
Free Memory:  1222  
Free Memory:  1120  
Free Memory:  1018  
Free Memory:  916  
Free Memory:  814  
Free Memory:  712  
Free Memory:  610  
Free Memory:  508  
Free Memory:  406  
Free Memory:  304  
Free Memory:  202  
Free Memory:  100  
Free Memory:  100  
Free Memory:  100

It looks like it uses 2 bytes more than the amount of memory you request (that sounds right, it has to store where the next piece of memory starts somewhere).

#5

What a great function! Thanks so much.

I added it to the output and it shows my memory usage doesn't change between program executions. It does however show I am working with very little spare sram and therefore I can now use this number to whittle it down.

:)

#6

Don't thank me.

Thank this guy! ]:) http://www.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Ddigital-text&field-keywords=arduuion+cookbook&x=0&y=0

It has been worth every penny. I know how to do everything he points out in the book. What I did not know was how to do it efficiently on an Arduino. Nor did I really understand the C++/C paradigm.

Ignorance is not bliss. It sucks!

#7

I think WillR intended this link: http://www.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Dstripbooks&field-keywords=arduino+cookbook&x=0&y=0

#8