Then I follow my two rules of embedded development: - no recursion - everything has to be O(1)

If I'm honest, I can't remember a project where I had to use even a pool allocator, which you would usually need if you were trying to do like, reorderable queues / lists / trees or so. I right now can't come up with a proper use case. If you do need to say, compute a variable length sequence of actions based on an incoming packet, then I would structure my code so that:

a) only the current action and the next action get computed (so that there is no pause in between executing them)

b) compute the next action when I switch over (basically with a ping-pong buffer)

c) verify real-time invariants

My most used structure is the ring buffer to smooth out "semi-realtime" stuff, and if the ring buffer overflows, well, the ring buffer overflows and it has to be dealt with. If I could have more memory I would just make the ring buffer bigger.

I'm not sure how clear this explanation is :)