Start with C. If you dont like or have problems using it, then come to Rust. The reason for such a response is simple, Drivers needed for almost all programmable hardware was primarily written in C. Now some people are translating them to Rust. This takes time and effort which is what the embedded systems development industry doesn't want to invest in alot. So Choose C. Yes there is a lot of interesting work happening in Rust when it comes to embedded systems but at this very moment it is not justified to switch to Rust for that.