embedded-trainings-2020/embedded-workshop-book/src/parts-embedded-program.md

Parts of an Embedded Program

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

✅ Open the beginner/apps folder in VS Code.

$ # or use "File > Open Folder" in VS Code
$ code beginner/apps

✅ Then open the src/bin/hello.rs file.

NOTE: If you find it more convenient to open the repository at the root then please also add the beginner/apps folder to the VS Code workspace: right click the left side panel, select "Add folder to workspace" and add the beginner/apps folder.

In the file, you will find the following attributes:

#![no_std]

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

#[entry]

The #[entry] attribute declares 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.