Yeah. I don't understand the choice of Rust in this context. If you can write all the CPU instructions on a whiteboard that also has the literal memory map you don't need a high level language like Rust.

I don't see this as a place where Rust can't replace C (or where Zig is a better replacement, or whatever) because why are we writing any high level language at all?

I guess it can make sense if there's a device family and this is the smallest of a range.