Parts of an Embedded Program

We will look at the elements that distinguish an embedded Rust program from a desktop program.

✅ Open the nrf52-code/radio-app folder in VS Code.

# or use "File > Open Folder" in VS Code
code nrf52-code/radio-app

✅ Then open the nrf52-code/radio-app/src/bin/hello.rs file.

Attributes

In the file, you will find the following attributes:

#![no_std]

The #![no_std] language attribute indicates that the program will not make use of the standard library, the std crate. Instead it will use the core library, a subset of the standard library that does not depend on an underlying operating system (OS).

#![no_main]

The #![no_main] language attribute indicates that the program will use a custom entry point instead of the default fn main() { .. } one.

#[entry]

The #[entry] macro attribute marks the custom entry point of the program. The entry point must be a divergent function whose return type is the never type !. The function is not allowed to return; therefore the program is not allowed to terminate. The macro comes from the cortex-m-rt crate and is not part of the Rust language.