Pro lesson · Preview

The HAL Pattern

Abstract a peripheral behind an interface so app logic survives an MCU swap and runs in a PC unit test, using runtime virtuals or zero-overhead compile-time polymorphism.

25 min read

In this lesson:

the HAL pattern, separate what hardware does from how a chip does it
runtime polymorphism (virtual interface), flexible, testable, small cost
compile-time polymorphism (templates / CRTP), zero overhead, type fixed early
the testability payoff: run firmware logic in a PC unit test with a fake
choosing between the two, and not over-abstracting

This is the capstone: it combines classes, RAII, references, const, and templates into the pattern that makes firmware portable and testable.

This lesson is part of Pro

Upgrade to unlock the full lesson and the complete interview Q&A.

Unlock with Pro

5 interview questions on this topic

Each one opens a full worked answer.

What is a HAL and what problem does it solve?What's the difference between runtime and compile-time polymorphism for a HAL, and when do you use each?Why does an abstract base class need a virtual destructor?How does the HAL pattern make firmware testable, and why does that matter?What's the downside of the HAL pattern, and how do you avoid over-abstracting?

This is just the start

More in C++ for Embedded

C++ vs C for Embedded Classes & Encapsulation Constructors, Destructors & RAII

References vs Pointers

const Correctness & constexpr

Function & Operator Overloading

The HAL Pattern | EmbeddedPrep.io