Another point if i may , not going into details, but just as a "general idea". Context is that im preparing a presentation about using Rust in embedded for mainly C programmers:

Among many points, one i really like in Rust is that the manipulation of static mutable variables is not so "free" as with C or C++ -> nice to avoid data races.

However when working without a "real time framework" like RTIC or Embassy,  the standard solution of Mutex<Refcell...> seems both unergonomic and quite expensive in terms of runtime...
Do RTIC and embassy handle the static mutable data sharing in a more efficient way behind the scenes? If so, that requires then Rust unsafe right?