Assignment 1: GPIO

Time to get hands-on. In this module, you’ll apply the Instantiate → Configure → Control pattern to GPIO — the most fundamental peripheral on any microcontroller.

GPIO Foundations

#

What is GPIO?

#

General Purpose Input/Output — the standard digital interface to the outer world. The most basic peripheral: making pins go high or low, and reading whether they’re high or low.

Configurations: Direction

#

• Output — you drive the pin (e.g., turn on an LED)
• Input — you read the pin (e.g., detect a button press)

Output Modes

#

• Push-pull (typically default) — actively drives the pin high and low
• Open-drain — actively drives low, but floats when “high” (needs external pull-up)

Drive Strength: How much current the pin can source or sink. Higher drive strength = brighter LED, but more power consumption.

This article is also a good reference for more detail about output modes.

Input Pull Resistors

#

• Pull-up — pin reads high when nothing is connected; button pulls it low
• Pull-down — pin reads low when nothing is connected; button pulls it high
• Floating — no pull resistor; pin state is undefined when nothing is connected

Exercise A: Blinky

#

Goal: Get an LED blinking by finding and adapting an existing example from the esp-hal documentation.

1. Create a New Project

#

esp-generate --chip esp32c3 -o unstable-hal -o vscode -o esp-backtrace -o log --headless gpio_blinky
cd gpio_blinky

2. Find the Example

#

Navigate to the esp-hal GPIO documentation.

Look for a blinky example — check:

• The module-level documentation (esp_hal::gpio)
• The Output struct page
• The esp-hal examples directory on GitHub

3. Apply the Mental Model

#

Read the example and identify:

• Instantiate — How is the Output created? What arguments does it take?
• Configure — What configuration is applied? (Level, OutputConfig)
• Control — What method is used to change the LED state?

4. Adapt to Your Hardware

#

• Check your board’s pinout for the LED pin
• Update the GPIO pin in the example to match
• Make sure the initial level matches your hardware (active high or active low?)

5. Build and Flash

#

cargo build --release
espflash flash target/riscv32imc-unknown-none-elf/release/gpio_blinky --monitor

Alternatively, you can build and flash using either one of the following commands:

cargo run --release
# or
cargo r -r

Exercise B: Button Input

#

Goal: Read a physical button press and use it to control the LED. You’ll need to find the Input abstraction and configure it correctly.

1. Create a New Project

#

esp-generate --chip esp32c3 -o unstable-hal -o vscode -o esp-backtrace -o log --headless gpio_button
cd gpio_button

2. Find the Input Abstraction

#

Navigate to the esp-hal GPIO documentation.

• Find the Input struct
• Read what arguments its constructor takes
• Look at what configuration options are available

3. Understand the Hardware

#

The button is wired to pull the pin to ground when pressed:

• When not pressed: pin floats (needs pull-up to read high)
• When pressed: pin is pulled low

This means you need a pull-up resistor configuration and detect a low level to know the button is pressed.

4. Configure the Input

#

Apply the mental model:

• Instantiate — Create an Input instance for the button pin
• Configure — Set the pull resistor to pull-up

Check the InputConfig struct and its methods. How do you set the pull direction?

5. Read the Button and Control the LED

#

Find the method on Input that reads the current pin state. Use it to:

• Detect when the button is pressed (low)
• Turn on the LED when pressed
• Turn off the LED when released

6. Build and Flash

#

cargo build --release
espflash flash target/riscv32imc-unknown-none-elf/release/gpio_button --monitor

Exercise C: Alternative Blink

#

Goal: Find a different way to achieve the same blink behavior, without using the same approach as in Exercise A.

1. Create a New Project

#

esp-generate --chip esp32c3 -o unstable-hal -o vscode -o esp-backtrace -o log --headless gpio_challenge
cd gpio_challenge

2. Explore the Output Documentation

#

Go back to the Output struct documentation and scroll through all the available methods.

3. Find an Alternative

#

The blinky example in Exercise A used one specific approach. Your task: find a different method that achieves the same result.

Hints:

• There’s more than one way to change pin state
• Some methods combine multiple operations
• Check both the inherent methods and the trait methods

4. Modify and Test

#

Update your blinky code to use the alternative approach. The LED should still blink at the same rate.

cargo build --release
espflash flash target/riscv32imc-unknown-none-elf/release/gpio_challenge --monitor

Cross-HAL Comparison

#

How do other HALs handle GPIO? Navigate the documentation for these two libraries and find how they approach the same tasks:

• rp2040-hal
• stm32f4xx-hal

Compare how each HAL handles Instantiate, Configure, and Control for GPIO.