Checking for memory usage on runtime

[maxpaynner]

Hey everyone,

I'm having problems with my app's ram usage as you can see from my previous questions.

I've tried this little piece of code:

void memcheck(void){
	// perform free memory check
	int blockSize = 16;
	int i = 1;
	debug("Checking memory with blocksize %d char ...\n", blockSize);
	while (true) {
		char *p = (char *) malloc(i * blockSize);
		if (p == NULL){
			break;
		}
		free(p);
		++i;
	}
	debug("Ok for %d char\n", (i - 1) * blockSize);
}

That I found here to test for free memory.

I get this output:

Test for free memory Checking memory

with blocksize 16 char ...

Ok for 4752 char

And then my application just breaks. I've checked and it seems to me that the memory that was mallock'd should be freed, so I don't understand where this is wrong. What's more interesting is that this behavior is eerily similar to the behavior I get when I try running the lwip stack alongside my app (see here and here).

Can you guys help me understand what is going on here?

[Susheel Nuguru]

does not look like your application is crashing because of this code. I copy pasted your code and it works fine and no crash. App is still alive. Find out where exactly it crashed.

[Dan Danknick]

Just to be clear here, you're testing the size of the heap space allocated during link time and not exactly the RAM usage of your app. Take a look in the file arm_startup_nrf51.s for your project and the label Heap_Size near the top. It is either set with an EQU statement or assigned a value passed in from the project settings of the build environment.

I also agree with Aryan that it doesn't appear your app is "breaking" - you should explain what that means in greater detail.

Dan

[maxpaynner]

I'm using app timers (from app_timer.h) to process data every second. If I use this code, those timers stop working. That's the problem I'm experiencing, sorry if it was unclear.

[maxpaynner]

Hey Dan,

Thing is I'm using this

STACK_N_HEAP = -D__HEAP_SIZE=1208 -D__STACK_SIZE=1024

in my makefile.

How can the heap grow to 4kb?

That STACK_N_HEAP flag is added to CFLAGS and ASMFLAGS further down in the makefile

[Susheel Nuguru]

app_timers use stack memory buffers and when you do malloc, the library creates more memory per block request to do book keeping. if heap allocation is affecting app_timers (which does not use heap) then the only reason i can see is that either malloc has moved into stack space or there was no enough stack space for app_timers and they used some heap space. decreasing heap_size and increasing stack size should solve your problem. Like Dan said you should change also change these in arm_startup_nrf51.s