[Animats]

That's because there's no language syntax for device address space. Modula had DEVICE as a keyword, and you could define structures as being in device space.

That's a useful language feature for low-level programming. It tells the compiler that the address space is special - it can change without help from the program. Other features of device space can include that the write width can matter (some registers have to be written as a single byte, world, or double word) and some registers are read-only or write-only. The compiler needs to know this stuff. Especially because Rust makes some strong assumptions about memory.

Rust probably needs to know about both device registers and memory shared with peripherals to operate at this level. For the blinky light program it doesn't matter; for the network stack it matters a lot.