5. Summary of Steps

Initial target-independent steps for creating a new crate

This first step is not AVR specific.

# Create a new binary project. You may also create a new library project with '--lib'.
cargo new --bin my-new-project
cd my-new-project

# AVR requires the nightly compiler
rustup override set nightly

Step 1. Adding a target specification JSON file for AVR

Compared to most Rust targets like X86 or ARM, the AVR family of microcontrollers cannot be cleanly modelled under different "families" of chips that are ELF-compatible. This is due to the fact that there are special variants of chips with nonstandard ISA support, as well as the ELF e_flags field which has a value that also has special cases for certain microcontrollers.

The upstream Rust compiler does not provide built-in targets for specific AVR microcontrollers. Instead, a target specification JSON file targeting a specific AVR device must be passed to Rust and Cargo.

Here are the steps for creating and using a target specification JSON file for AVR.

Step 2. Adding the #[no_std] attribute to your crate root

Like many embedded targets, the standard library is not supported and so it must be opted out of.

Step 3. Creating an executable entry point with #[no_main]

As we are using the device-specific startup runtime libraries for C/C++ under AVR-GCC, we must bypass Rust's usual handling of the main function so that the main function is correctly picked up by the GCC startup libraries.

Step 4. Choosing an input/output library

Use an existing library or write your own - your choice.

Recommended is embedded-hal, which provides a architecture-independent way to expose GPIO pins and peripherals that works across devices such as AVR and ARM.

Step N. - More documentation is on its way. In the meantime, avr-rust/blink serves as a reference implementation