code not in line with description. Use comments of code to comment about code, not to give alternative code

[flip111]

https://rust-embedded.github.io/book/start/qemu.html#a-non-standard-rust-program

extern crate panic_halt;. This crate provides a panic_handler that defines the panicking behavior of the program. More on this later on.

Above that:

// pick a panicking behavior
extern crate panic_halt; // you can put a breakpoint on `rust_begin_unwind` to catch panics
// extern crate panic_abort; // requires nightly
// extern crate panic_itm; // logs messages over ITM; requires ITM support
// extern crate panic_semihosting; // logs messages to the host stderr; requires a debugger

If it's gonna be later, put it later, don't add noise in code comments.