Creating a Hardware Abstraction Layer (HAL) in C

Creating a Hardware Abstraction Layer (HAL) in C

Jacob Beningo

TimelessIntermediate

In my last post, C to C++: Using Abstract Interfaces to Create Hardware Abstraction Layers (HAL), I discussed how vital hardware abstraction layers are and how to use a C++ abstract interface to create them. You may be thinking, that’s great for C++, but I work in C! How do I create a HAL that can easily swap in and out different drivers? In today’s post, I will walk through exactly how to do that while using the I2C bus as an example.

Summary

This blog post shows how to implement a Hardware Abstraction Layer (HAL) in C, using the I2C bus as a running example. It explains patterns and idioms—such as function-pointer-based interfaces and dependency injection—that make drivers swappable, testable, and portable across microcontrollers.

Key Takeaways

Implement a HAL in C using structures of function pointers to define consistent driver interfaces.
Design swappable I2C drivers so hardware-specific code can be replaced without changing application logic.
Apply dependency injection techniques to select and initialize drivers at build or runtime.
Write drivers to be testable and mockable to enable unit testing of higher-level firmware.