Bare Metal (no_std)

Using no_std may be more familiar to embedded Rust developers; it does not use std (the Rust standard library) but instead uses a subset, the core library. The official Rust embedded book has a great section on this.

It's important to note that in general a no_std crate can always compile in std environment but the inverse is not true. Therefore, when creating crates it's worth keeping in mind if it needs the standard library to function.

Hardware Abstraction Layers

Previously, the primary focus of no_std development was the ESP32 and (to a lesser extent) the ESP8266.

Now there is a renewed effort to implement no_std support for the entire lineup of Espressif devices from the ESP32 and newer. These new HALs can be found in the esp-rs/esp-hal repository.

There is also some level of support for Wi-Fi and Bluetooth via esp-rs/esp-wifi for ESP32, ESP32-C3, ESP32-S2, and ESP32-S3.

Chip Support

Chip support for no_std requires LLVM/Clang support just like for std. However, this has no dependency on esp-idf. In addition to compiler support, it's necessary to have peripheral access crates (PAC) and hardware abstraction layers (HAL) for your desired chip.

Refer to the table below to see if your chip is supported. Please note that the no_std HALs are still in the early phases of development, so not all peripherals have had drivers implemented.

Relevant esp-rs Crates