Stack size using Heap 2

nobody wrote on Tuesday, September 06, 2005:

A friend myself recently completed porting freeRTOS onto a AVR Mega16, using timer 0 as the main clock timer as we wanted to user timer 1 for PWM’s.   This particular part only has 1k of ram, so we are concerned with the number of tasks which may run currently and also stack size.

Question is this:

We would like to use the Heap_2 memory management strategy and delete and create tasks on the fly, so our main concern is fragmentation.

If we use the minimum stack size (83 bytes), will this work?

Does the stack size vary dynamically?

What are the concerns?


rtel wrote on Thursday, September 08, 2005:

Sorry for the delay in responding  but I have been out of the office for the last 4 days.

Have you seen the following page?

These figures were taken on an AVR using GCC.

1K is really a very small amount of RAM to have available.  What you can do with it will depend on what else is using RAM in your system.  Take a look at the application design pages of the FreeRTOS site for ideas on minimising RAM usage:

I would suggest adding a few lines at the bottom of the pvPortMalloc() in heap_2.c to test whether NULL is returned (indicating that there is insufficient memory available).  You can then set a break point on the line (if NULL is returned) to immediately know if you are running out of memory.


nobody wrote on Friday, September 09, 2005:

Thanks Richard,

that’s a a good suggestion.