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extend hal explanation

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Lotte Steenbrink 2021-04-20 13:34:49 +02:00
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16
embedded-workshop-book/src/using-hal.md
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@ -2,7 +2,17 @@
Open the `src/bin/led.rs` file.
The `dk` crate / library is a Hardware Abstraction Layer (HAL) over the nRF52840 Development Kit. The purpose of a HAL is to abstract away the device-specific details of the hardware, for example registers, and instead expose a higher level API more suitable for application development.
You'll see that it initializes your board using the `dk` crate:
```rust
let board = dk::init().unwrap();
```
This grants you access to the board's peripherals, like its LEDs.
The `dk` crate / library is a Board Support Crate tailored to this workshop to make accessing the peripherals used in this workshop extra seamless.
You can find its source code at `boards/dk/src/`.
`dk` is based on the [`nrf52840-hal`] crate, which is a Hardware Abstraction Layer (HAL) over the nRF52840 Development Kit. The purpose of a HAL is to abstract away the device-specific details of the hardware, for example registers, and instead expose a higher level API more suitable for application development.
The `dk::init` function we have been calling in all programs initializes a few of the nRF52840 peripherals and returns a `Board` structure that provides access to those peripherals. We'll first look at the `Leds` API.
@ -24,4 +34,8 @@ Among the logs you'll find the line "I/O pins have been configured for digital o
After the `dk::init` logs you'll find logs about the `Led` API. As the logs indicate an LED becomes active when the output of the pin is a *logical zero*, which is also referred as the "low" state. This "active low" configuration does not apply to all boards: it depends on how the pins have been wired to the LEDs. You should refer to the [board documentation] to find out which pins are connected to LEDs and whether "active low" or "active high" applies to it.
🔎 When writing your own embedded project, you can implement your own convenience layer similar to `dk`, or use the matching HAL crate for your board directly. Check out [awesome-embedded-rust] if there's a HAL crate for the board you'd like to use.
[`nrf52840-hal`]: https://docs.rs/nrf52840-hal/0.12.1/nrf52840_hal/
[board documentation]: https://infocenter.nordicsemi.com/index.jsp?topic=%2Fug_nrf52840_dk%2FUG%2Fnrf52840_DK%2Fintro.html
[awesome-embedded-rust]: https://github.com/rust-embedded/awesome-embedded-rust#hal-implementation-crates