Dependencies

nrf-softdevice crate

This crate provides Rust bindings for Nordic's closed-source SoftDevice Bluetooth stack. The SoftDevice is a precompiled C binary that runs first on startup and then hands control to your app. It's battle tested, pre qualified for bluetooth certification. Learn more: nrf-softdevice GitHub.

We will use this crate to handle Bluetooth in our project. To use it, we must specify the following features for the crate:

• Exactly one SoftDevice model. Depending on the model, the crate supports different roles. The micro:bit uses the s113 SoftDevice, so we will have to use that. For this model, the crate supports only the peripheral role. It does not support central mode.

• Exactly one supported nRF chip. For the micro:bit, we already know it uses the nrf52833.

So, we will have to update the Cargo.toml with the following dependencies:

# nrf-softdevice = { version = "0.1.0", features = ["ble-peripheral", "ble-gatt-server", "s113", "nrf52833", "critical-section-impl", "defmt"] }
# To fix a conflict issue, using this latest (at the moment) revision
nrf-softdevice = { git = "https://github.com/embassy-rs/nrf-softdevice/", rev = "5949a5b", features = [
    "ble-peripheral",
    "ble-gatt-server",
    "s113",
    "nrf52833",
    "defmt",
] }
nrf-softdevice-s113 = { version = "0.1.2" }

Along with that, we've enabled a few additional features like ble-peripheral and ble-gatt-server which are needed for our use case.

StaticCell crate

The "StaticCell" crate is useful when you need to initialize a variable at runtime but require it to have a static lifetime.

Update the Cargo.toml with the following dependencies:

static_cell = "2"

Heapless crate

The main idea behind the heapless crate is that it uses data structures that don't need dynamic memory (no heap). Instead, everything is stored in a fixed-size memory area.

Update the Cargo.toml with the following dependencies:

heapless = "0.8"

For example, heapless::Vec is like Rust's regular Vec, but with one big difference: it has a fixed maximum size that you decide ahead of time, and it can't grow beyond that. This is especially useful in Embedded Rust, where heap memory is often not available

Futures

The futures crate provides core tools for writing asynchronous code. We use "select!" and "pin_mut!" macros from it to run the battery level notifier and GATT server tasks concurrently.

futures = { version = "0.3.29", default-features = false }