Must FreeRTOS task stack size account for interrupt stack size?

Question

I have FreeRTOS running on a MKE06 Cortex-M0+ (based on SAMD20 demo), GCC toolchain. I am trying to figure out optimal task stack sizes (with the help of avstack.pl).

I want to use only static memory allocation. In the FAQ I have read this:

The stack requirements of interrupt service routines - which for many RTOS ports is zero as the RTOS will switch to use a dedicated interrupt stack on entry to an interrupt service routine.

I use this port. I don't know much assembly, but I think I do not see anything that would configure stack pointer separately for the interrupts (is such thing even supported by M0+?). I allocated stack for the idle task manually (with vApplicationGetIdleTaskMemory), but I did not find a function to provide stack space for interrupts. Interrupts work fine, I do not use nested interrupts.

My questions:

1. Should my task stack size be enlarged by at least the biggest possible interrupt stack size?
2. Can I allocate a separate interrupt stack on Cortex M0+ in plain C (ie. without adding own assembly to each ISR)?

Answer 1

Interrupt service routine will use the stack you are also using for main(). You have a stack defined in your linker script, this is the one used for main and ISR, separate from the stack of the FreeRTOS tasks.

Answer 2

When a Cortex-M0 device accepts an interrupt it automatically switches to use a different stack, so interrupts do not use any of the task's stack.

Make sure you use a stack overflow hook (http://www.freertos.org/Stacks-and-stack-overflow-checking.html) in case you get the size to small, and monitor actual stack usage (http://www.freertos.org/uxTaskGetStackHighWaterMark.html) to ensure you are not allocating too much.