In Rust, it is well-known that static mut is dangerous. The docs for the static keyword have this to say about mutable statics:
This makes perfect sense, so far. But my program is single threaded. I know it is single threaded because it runs on bare metal with no_std . I also know that I will need global state to manage access to memory-mapped I/O, and the global state needs to be mutable so that I can replace it at runtime. I can do this with static mut because I do not have to worry about data races with multiple threads right?
Well, that's the thought I initially had, anyway. And I believe I am not alone. But there is a lot of subtlety with static mut references that are problematic, even in a guaranteed single-threaded context. At first I believed it all has to do with the special 'static lifetime, but that is not the case. Rust By Example describes this lifetime as follows:
That also makes sense, and it's exactly what I want. In my case, the memory-mapped I/O that I wanted to control was a serial port. The primary goal was to reproduce something akin to standard I/O with println! and dbg! macros like those provided by the Rust standard library. A secondary goal was to make the sink configurable at runtime. This would allow the software to run on hardware with different serial interfaces, for example, without recompiling it for each distinct device.