Embedded Patterns

# Embedded Patterns

## Mental Model

Embedded Development All Follows a Similar Pattern

**Instantiate → Configure → Control**

We will adopt this as a Mental Model to navigate the Rust Ecosystem

---

## Peripheral Singletons

**Each Block is a Peripheral Singleton**

```rust
let peripherals = Peripherals::take().unwrap();
```

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---

## Instantiation

PAC Singletons are Promoted (passed to) to HAL abstraction instances

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## GPIO can be Tricky

Some HALs (Ex. esp-hal) provide abstractions at the **pin level**, not the GPIO block level

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## GPIO Instantiation Examples

How three different HALs instantiate a GPIO output pin:

**rp2040-hal**

```rust
let pac = pac::Peripherals::take()
    .unwrap();
let sio = Sio::new(pac.SIO);
let pins = Pins::new(
    pac.IO_BANK0,
    pac.PADS_BANK0,
    sio.gpio_bank0,
    &mut pac.RESETS,
);
let led = pins.gpio25
    .into_push_pull_output();
```

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**esp-hal**

```rust
let peripherals = esp_hal::init(
    Config::default()
);
let led = Output::new(
    peripherals.GPIO0,
    Level::High,
    OutputConfig::default(),
);
```

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**stm32f4xx-hal**

```rust
let pac = Peripherals::take()
    .unwrap();
let gpioa = pac.GPIOA.split();
let led = gpioa.pa5
    .into_push_pull_output();
```

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---

## Configure

The instance gives us **configure** and **control** methods

**rp2040-hal**

```rust
let button = pins.gpio15
    .into_pull_up_input();
```

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**esp-hal**

```rust
let button = Input::new(
    peripherals.GPIO9,
    InputConfig::default()
        .with_pull(Pull::Up),
);
```

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**stm32f4xx-hal**

```rust
let button = gpioa.pa0
    .into_pull_up_input();
```

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---

## Control

**rp2040-hal**

```rust
if button.is_high().unwrap() {
    led.set_high().unwrap();
}
```

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**esp-hal**

```rust
if button.is_high() {
    led.set_high();
}
```

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**stm32f4xx-hal**

```rust
if button.is_high() {
    led.set_high();
}
```

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---

## Things to Note

- HAL Peripheral instances are **drivers for microcontroller peripheral blocks**

- Off-controller device drivers (e.g. an I2C sensor) are a similar concept. They are instances that use microcontroller peripheral drivers to provide abstraction. Same concept as how peripherals use the PAC.

- Configuration is sometimes passed as an argument to the **instantiation** statement rather than as a separate step

- HALs often implement **embedded-hal** traits to provide device drivers with a common interface across controllers

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## embedded-hal in Practice

**esp-hal**

```rust
use bme280::Bme280;
use esp_hal::i2c::master::I2c;

let i2c = I2c::new(
    peripherals.I2C0,
    I2cConfig::default(),
);
let mut sensor = Bme280::new(i2c);
```

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**stm32f4xx-hal**

```rust
use bme280::Bme280;
use stm32f4xx_hal::i2c::I2c;

let i2c = I2c::new(
    pac.I2C1,
    (scl, sda),
    100.kHz(),
    &clocks,
);
let mut sensor = Bme280::new(i2c);
```

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**rp2040-hal**

```rust
use bme280::Bme280;
use rp2040_hal::I2C;

let i2c = I2C::i2c0(
    pac.I2C0,
    sda_pin, scl_pin,
    100.kHz(),
    &mut pac.RESETS,
    &clocks,
);
let mut sensor = Bme280::new(i2c);
```

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The Embedded Rustacean · Rust Week 2026