# Embassy STM32 HAL

The embassy-stm32 HAL aims to provide a safe, idiomatic hardware abstraction layer for all STM32 families. The HAL implements both blocking and async APIs for many peripherals. Where appropriate, traits from both blocking and asynchronous versions of [embedded-hal](https://docs.rs/embedded-hal/latest/embedded_hal/) v0.2 and v1.0 are implemented, as well as serial traits from embedded-io\[-async].

* [embassy-stm32 on crates.io](https://crates.io/crates/embassy-stm32)
* [Documentation](https://docs.embassy.dev/embassy-stm32/) (**Important:** use docs.embassy.dev rather than docs.rs to see the specific docs for the chip you’re using!)
* [Source](https://github.com/embassy-rs/embassy/tree/main/embassy-stm32)
* [Examples](https://github.com/embassy-rs/embassy/tree/main/examples)

## embassy-stm32 supports all STM32 chip families

STM32 microcontrollers come in many families and flavors, and supporting all of them is a big undertaking. Embassy takes advantage of the fact that the STM32 peripheral versions are shared across chip families. For example, instead of re-implementing the SPI peripheral for every STM32 chip family, embassy has a single SPI implementation that depends on code-generated register types that are identical for STM32 families with the same version of a given peripheral.

In practice, this works as follows:

1. You tell the compiler which chip you’re using with a feature flag
1. The stm32-metapac module generates register types for that chip at compile time, based on data from the stm32-data module
1. The embassy-stm32 HAL picks the correct implementation each peripheral based on automatically-generated feature flags, and applies any other tweaks which are required for the HAL to work on that chip

Be aware that, while embassy-stm32 strives to consistently support all peripherals across all chips, this approach can lead to slightly different APIs and capabilities being available on different families. Check the [documentation](https://docs.embassy.dev/embassy-stm32/) for the specific chip you’re using to confirm exactly what’s available.

## embassy-time Time Driver
If the `time` feature is enabled, embassy-stm32 provides a time driver for use with [embassy-time](https://docs.embassy.dev/embassy-time/). You can pick which hardware timer is used for this internally via the `time-driver-*` features, or let embassy pick with `time-driver-any`.

embassy-time has a default tick rate of 1MHz, which is fast enough to cause problems with the 16-bit timers currently supported by the embassy-stm32 time driver (specifically, if a critical section delays an IRQ by more than 32ms). To avoid this, it’s recommended to pick a lower tick rate. 32.768kHz is a reasonable default for many purposes.