Skip to content

Latest commit

 

History

History
58 lines (49 loc) · 2.3 KB

embedded_hal.md

File metadata and controls

58 lines (49 loc) · 2.3 KB

embedded-hal

This project contains Traits that are common to embedded devices.

The motivation for this can be thought of as if we look at what we did when
writing the assembly language programs for various devices, we had to specify
the registers used in each program (or include them from a common include file). We had to look these registers up in the datasheet for the microcontroller in
question.

To turn on an LED we need to perform some specific tasks for the microcontroller like enabling the PORT that the LED is connected to, set the mode, the output type, the speed and finally set/unset the PIN of the LED to turn it on. An example can be found in led-ext.s.

And in Rust we did something similar main.rs. The main point is that doing this over and over again is error prone and the code is not very nice or safe.

API reference

Take embedded_hal::digital::v2::InputPut which is a Trait:

pub trait InputPin {
    type Error;
    fn is_high(&self) -> Result<bool, Self::Error>;
    fn is_low(&self) -> Result<bool, Self::Error>;
}

We can see a concrete implementation of this in stm32f0xx-hal:

impl InputPin for Pin<Output<OpenDrain>> {
    type Error = Infallible;

    #[inline(always)]
    fn is_high(&self) -> Result<bool, Self::Error> {
        self.is_low().map(|v| !v)
    }

    #[inline(always)]
    fn is_low(&self) -> Result<bool, Self::Error> {
        Ok(unsafe { (*self.port).is_low(self.i) })
    }
}

A driver can write code using the interfaces/traits in embedded_hal and then someone wanting to use the driver can import any embedded-hal implemenation and still use the driver. Users of Drivers can the use/import a specific hal using:

use stm32f0xx_hal as hal;

If they want to switch to a different type of microcontroller they will only have to update the dependency in Cargo.toml and then replace stm32f0xx_hal with the name of that create instead.