Stack sizes in my Startup.s file

tjohansen wrote on Wednesday, July 01, 2009:


Im using FreeRTOS on a LPC2478 ARM7 microcontroller.
I have a question recarding stack sizes in my startup file.

Im using KEIL uVision as compiler and mem scheme 2 as memory manager.

As I understand, then the heap (in heap_2.c) is where createTask takes a chunk out every time a task is created. When a task is created the tasks stack size must be supplied. So the combined stack sizes of all the tasks must be smaller then the heap size, incl some task info (defined with configTOTAL_HEAP_SIZE). ???

The task runs in user mode (ARM7 CPU mode). In the startup.s file I can allocate stacks for each processor mode. So, if I’m right, then the user stack size in my startup.s file, must be at least my heap size? Or must it just be minimum my greates task stack size??


davedoors wrote on Wednesday, July 01, 2009:

You need to allocated space for the Supervisor stack and IRQ stack only.  FIQ stack needs to be allocated only if you use FIQ interrupts.  Tasks stacks as you rightly say come from the heap so you don’t need to allocate any user mode stacks.

There are lots of examples in the download for you to copy.