embedded-hal

A Hardware Abstraction Layer (HAL) for embedded systems

This project is developed and maintained by the HAL team.

Companion crates

The main embedded-hal crate contains only blocking traits, where the operation is done synchronously before returning. Check out the following crates, which contain versions of the traits for other execution models:

• embedded-hal-async: async/await-based.
• embedded-hal-nb: polling-based, using the nb crate.

The embedded-hal-bus crate provides utilities for sharing SPI and I2C buses.

Additionally, more domain-specific traits are available in separate crates:

• embedded-can: Controller Area Network (CAN)
• embedded-io: I/O byte streams (like std::io, but no-std-compatible).

Serial/UART traits

There is no serial traits in embedded-hal. Instead, use embedded-io. A serial port is essentially a byte-oriented stream, and that's what embedded-io models. Sharing the traits with all byte streams has some advantages. For example, it allows generic code providing a command-line interface or a console to operate either on hardware serial ports or on virtual ones like Telnet or USB CDC-ACM.

Design goals

The HAL

• Must erase device specific details. Neither register, register blocks, nor magic values should appear in the API.

• Must be generic within a device and across devices. The API to use a serial interface must be the same regardless of whether the implementation uses the USART1 or UART4 peripheral of a device or the UART0 peripheral of another device.

• Where possible must not be tied to a specific asynchronous model. The API should be usable in blocking mode, with the futures model, with an async/await model or with a callback model. (cf. the nb crate)

• Must be minimal, and thus easy to implement and zero cost, yet highly composable. People that want higher level abstraction should prefer to use this HAL rather than re-implement register manipulation code.

• Serve as a foundation for building an ecosystem of platform-agnostic drivers. Here driver means a library crate that lets a target platform interface an external device like a digital sensor or a wireless transceiver. The advantage of this system is that by writing the driver as a generic library on top of embedded-hal driver authors can support any number of target platforms (e.g. Cortex-M microcontrollers, AVR microcontrollers, embedded Linux, etc.). The advantage for application developers is that by adopting embedded-hal they can unlock all these drivers for their platform.

• Trait methods must be fallible so that they can be used in any possible situation. Nevertheless, HAL implementations can additionally provide infallible versions of the same methods if they can never fail in their platform. This way, generic code can use the fallible abstractions provided here but platform-specific code can avoid fallibility-related boilerplate if possible.

Out of scope

• Initialization and configuration stuff like "ensure this serial interface and that SPI interface are not using the same pins". The HAL will focus on doing I/O.

Platform agnostic drivers

You can find platform-agnostic drivers built on top of embedded-hal on crates.io by searching for the embedded-hal keyword.

If you are writing a platform-agnostic driver yourself you are highly encouraged to add the embedded-hal keyword to your crate before publishing it!

Optional Cargo features

• defmt-03: Derive defmt::Format from defmt 0.3 for enums and structs.

Minimum Supported Rust Version (MSRV)

This crate is guaranteed to compile on stable Rust 1.60 and up. It might compile with older versions but that may change in any new patch release.

See here for details on how the MSRV may be upgraded.

License

Licensed under either of

• Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.

Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.