I’m writing a firmware for a Atmel XMEGA microcontroller in c and I think I filled up the 4 KB of SRAM. As far as I know I only do have static/global data and local stack variables (I don’t use malloc within my code).
I use a local variable to buffer some pixel data. If I increase the buffer to 51 bytes my display is showing strange results – a buffer of 6 bytes is doing fine. This is why I think my ram is full and the stack is overwriting something.
Creating more free memory is not my problem because I can just move some static data into the flash and only load it when its needed. What bothers me is the fact that I could have never discovered that the memory got full.
Is it somehow possible to dected (e.g. by reseting the microcontroller) when the memory got filled up instead of letting it overwrite some other data?
It can be very difficult to predict exactly how much stack you’ll need (some toolchains can have a go at this if you turn on the right options, but it’s only ever a rough guide).
A common way of checking on the state of the stack is to fill it completely with a known value at startup, run the code as hard/long as you can, and then see how much had not been overwritten.
The startup code for your toolchain might even have an option to fill the stack for you.
Unfortunately, although the concepts are very simple: fill the stack with a known value, count the number of those values which remain, the reality of implementing it can require quite a deep understanding of the way your specific tools (particularly the startup code and the linker) work.
Crude ways to check if stack overflow is what’s causing your problem are to make all your local arrays ‘static’ and/or to hugely increase the size of the stack and then see if things work better. These can both be difficult to do on small embedded systems.