Any information on SRAM usage after compilation?

Hi there,

My Mega 2560 board should have 8kB of SRAM. I wrote a very comprehensive program of about 200k program size that uses up also a large SRAM space. It is getting really tight now and I need to squeeze more SRAM space.
The problem I have is; the compiler doesn't give any information on the SRAM usage and the compilation is always successful even the memory usage has already over 8kB, this results in crash when running some sections of code.
May I ask if there is a possibility the compiler can give out information on total SRAM usage for both static buffers, dynamically created buffers or even the stack size?


The compiler has no idea what functions may be called, and cannot predict stack usage. If you know any computer science, this is equivalent to the halting problem.

In fact yes, but its a little long route and I just read about it today.

  1. You can enable verbose mode in preferences.txt to find out where the temporary files are stored (you have to hold shift key during compilation to view it).

2)Now navigate to the temporary folder through commandline.

3)You will see a file with following format in there <sketch_name>.cpp.elf

4)type avr-size -C --mcu=m2560 <sketch_name>.cpp.elf in commandline and hit enter. Hopefully it should return the information you want.Test this and reply back.

No news on this??

I can provide some update of this problem. I hope that it will be helpful for somebody.

Utility avr-size evaluates size of constant data and unitialized global and static data. As was mentioned above, form avr-size output, sum of data and bss provide this result. But there is no info about data stored in stack and allocated data in heap, which are dynamically creted/erased during program run (see AVR Libc help, chapter "Memory Areas and Using malloc()" for details). Compiler doesn't know anything about it, of course. There is a way how to analyse free memory during program run, here is an example:

// --------------------------------------------------------------------------------------
// **************
// *  FreeSRAM  *
// **************
// Evaluate an amount of SRAM free space (include free fragments in heap)


/* free list structure as maintained by the avr-libc memory allocation routines */
struct __freelist {
	size_t sz;
	struct __freelist *nx;

unsigned int FreeSRAM()
unsigned int free_memory = (unsigned int)&free_memory + sizeof(free_memory);
										// the last element in stack, so its address is
										// current pointer to end of stack

	#if defined (__AVR__)

	extern unsigned int __heap_start;	// beginning of allocation heap
	extern void *__brkval;				// current end of heap (0 if no allocation yet)
	extern struct __freelist *__flp;	// head of the free list structure

		if(__brkval == 0) free_memory -= (unsigned int)&__heap_start;
		  else {          free_memory -= (unsigned int)__brkval;

		/* add all free memory fragments if any */
			for(struct __freelist *current = __flp; current; current = current->nx) {
				free_memory += 2;		// two bytes for the memory block's header
				free_memory += (unsigned int)current->sz;



/*                           *** ATmega2560 Data Memory ***

	0x0000 - 0x001F		32 Registers (1 byte each)
	0x0020 - 0x005F		64 I/O Registers
	0x0060 - 0x01FF		416 Ext I/O Registers
	0x0200 - 0x21FF		Internal SRAM 8192 bytes
	0x2200 - 0xFFFF		External SRAM 0 - 64 kb

	Internal SRAM:

	0x0200 - bottom of RAM			.data variables (contains static data which was
									defined in code)
	__data_end == __bss_start		.bss variables  (uninitialized global or static
									variables end up in the .bss section)
	__bss_end  == __heap_start		heap for dynamic allocation - malloc()
	__brkval						end of heap
	...								free memory
	SP (stack pointer)				local variables
	0x21FF - top of RAM (RAMEND)	stack is started from the top of internal RAM

#endif // _DEBUG_FREE_SRAM

ATmega2560 has a feature which allows to connect and use an external SRAM (see datasheet for details). I found this: arduino | Andys Workshop on web. There is nice example how to expand ATmega2560's memory size.