To Program or Not to Program with HAL?

Dear Embedded Engineer,

You should ABSOLUTELY, MAYBE, or NEVER use a Hardware Abstraction Layer (HAL) when programming your microcontroller!?

Two weeks ago, I asked a LinkedIn question about the utility of HAL. Approximately 100 of you graciously responded. I thank you for taking time out of your busy schedule to share your valuable insights about this important topic.?

Your responses were split down the middle with a slight advantage to the “don’t use HAL” argument. This was especially true for safety critical applications that required extensive testing.

To clarify and consolidate your responses, we call on OpenAI's ChatGPT to do what it does best. The remainder of this article is written by GPT 4o at 10:20 PM on the 29th of January 2025. It summarizes your responses, identifies the top 10 tips, and then provides recommendation for each category of programmer.

Again, I learned so much from the LinkedIn community. I extend a big warm THANK YOU!

Be sure to read the original comments as there are many nuanced points likely to be missed in a human or AI written summary.

Take it away GPT 4o...

Sincerely,

Aaron

For Using HAL – Summary:

Many programmers favor using a Hardware Abstraction Layer (HAL) because it optimizes development time, allowing projects to progress faster without needing deep knowledge of hardware-level programming. HAL simplifies tasks like configuring peripherals and managing microcontroller resources, which can otherwise take hours or days when working with complex devices. This efficiency is crucial in environments where deadlines are tight or when developers need to quickly prototype and iterate on designs. HAL also ensures code portability, making it easier to migrate applications across different hardware within the same manufacturer’s ecosystem, an important consideration for product scalability.

From an education and safety perspective, HAL provides an accessible on-ramp for less experienced developers and new hires who may not have the expertise to write low-level code. By abstracting hardware details, HAL minimizes the chances of introducing bugs that result from incorrect register configurations. This abstraction provides an extra safety layer by ensuring the hardware operates within manufacturer-recommended parameters, reducing risks associated with improper configurations. Developers using HAL often highlight that it supports collaborative development where teams can focus on application logic without needing individual team members to master the microcontroller’s intricate details.

Top 10 Arguments For HAL:

1. Development Time Savings: Speeds up configuration and coding by abstracting low-level details.
2. Code Portability: Allows applications to be easily transferred between boards or microcontrollers from the same vendor.
3. Rapid Prototyping: Essential for quickly creating and testing proof-of-concept designs.
4. Reduced Complexity: Simplifies the configuration of peripherals, making development less error-prone.
5. Reliable Manufacturer Updates: Fixes and optimizations provided by the manufacturer improve hardware interactions.
6. Easier Team Collaboration: Developers can focus on high-level tasks without requiring everyone to understand hardware specifics.
7. Safety and Stability: Reduces the risk of hardware misconfiguration, especially for critical systems.
8. Mix of High-Level and Low-Level Control: Developers can combine HAL with bare-metal code as needed.
9. Scalability: Enables expanding project functionality through reusable libraries.
10. Educational Benefits: Provides a learning path for students and junior engineers entering embedded systems.

Against Using HAL – Summary:

Programmers against HAL often cite performance concerns and the potential for inefficiency due to the extra layers of abstraction. HAL-based programs tend to consume more memory and CPU cycles, making them unsuitable for time-sensitive applications like real-time control systems or applications requiring precise timing. Developers also point out that HAL implementations often generate bloated, overly complex code, which is harder to debug and maintain. For those working in systems where efficiency and predictability are paramount, the overhead introduced by HAL is seen as a liability rather than an asset.

Opponents of HAL also emphasize education and long-term maintainability, arguing that reliance on HAL can stunt a programmer’s understanding of hardware and hinder the development of efficient, custom solutions. By bypassing the learning curve associated with low-level programming, developers may miss out on understanding the hardware’s full potential. Programmers who prioritize control and transparency prefer manually configuring Special Function Registers (SFRs) because they know every line of code, making it easier to troubleshoot and optimize. Many experienced engineers argue that bare-metal programming leads to simpler, cleaner, and more maintainable code in the long run, particularly for real-time applications.

Top 10 Arguments Against HAL:

1. Performance Overhead: HAL introduces latency and resource consumption, unsuitable for real-time tasks.
2. Bloat and Inefficiency: HAL often generates large, nested, and inefficient code structures.
3. Limited Customization: HAL does not always expose all microcontroller features, limiting fine-tuning.
4. Opaque Code Layers: Debugging nested HAL calls is more challenging compared to bare-metal.
5. Lack of Full Control: Developers sacrifice control over hardware optimizations when using HAL.
6. Long-Term Maintainability: Custom drivers are often smaller, easier to understand, and more maintainable.
7. Educational Limitations: Overreliance on HAL can prevent programmers from understanding hardware behavior.
8. Hardware Dependency: HAL often locks developers into a manufacturer’s ecosystem and versioning.
9. Complexity in Debugging: Finding and fixing errors in HAL can be harder due to opaque abstractions.
10. Memory and Resource Consumption: HAL’s abstraction increases memory usage, requiring more expensive hardware.

Guidelines for Choosing HAL vs Bare-Metal Programming Based on Project Types

1. Students and Novices

Recommended Approach: Start with HAL, transition to bare-metal when needed.

Rationale: HAL provides an accessible entry point for beginners to understand microcontroller basics without being overwhelmed by hardware complexities. As they progress, students should explore bare-metal programming to gain a deeper understanding of registers, timing, and hardware configurations.

Key Factors:

• Educational Value: HAL introduces embedded systems while simplifying early development tasks.
• Learning Curve: Students can transition from HAL to bare-metal once they understand the fundamentals.

2. Prototype Design (Proof-of-Concept, Rapid Development)

Recommended Approach: HAL is generally preferred.

Rationale: Rapid prototyping benefits from the speed and simplicity of HAL, allowing teams to quickly demonstrate functionality without spending time manually configuring registers.

Key Factors:

• Development Time: HAL speeds up development when time-to-market is critical.
• Flexibility: Developers can switch between HAL and bare-metal if needed during iteration cycles.
• Portability: The ability to quickly port designs across different boards is crucial during prototyping.

3. Production Design (Long-Term Maintainability)

Recommended Approach: Bare-metal or a combination of HAL and custom drivers.

Rationale: For production systems, maintainability, efficiency, and long-term reliability are key considerations. Bare-metal is preferred when performance and precise control are critical, but HAL may still be used for non-performance-critical peripherals.

Key Factors:

• Maintainability: Bare-metal code is often smaller, easier to debug, and more maintainable in the long run.
• Customizability: Developers have full control over hardware configurations with bare-metal.
• Portability vs. Performance: Some teams may use HAL selectively to achieve a balance.

4. Safety-Critical Systems (Aerospace, Medical, Automotive)

Recommended Approach: Primarily bare-metal with minimal HAL use for non-critical tasks.

Rationale: Safety-critical applications demand precise control, minimal latency, and high reliability. Bare-metal programming ensures that the code is fully deterministic and tailored for specific performance and safety requirements.

Key Factors:

• Real-Time Performance: Bare-metal allows direct control over hardware for deterministic behavior.
• Verification and Validation: Bare-metal code is easier to fully analyze and test.
• Minimal Abstraction: HAL introduces complexity and risks that can be avoided in safety-critical applications.

5. Mixed Applications (Hybrid Systems with High and Low Complexity)

Recommended Approach: Use a combination of HAL and bare-metal.

Rationale: Many embedded applications have components with varying performance requirements. Developers can use HAL for non-critical tasks like communication and basic I/O while employing bare-metal for timing-critical operations.

Key Factors:

• Selective HAL Use: Balance ease of development with performance needs.
• Reduced Complexity: HAL simplifies non-critical aspects without affecting system reliability.
• Flexibility: Developers can shift towards bare-metal in critical sections if needed.

6. Performance-Critical Systems (Real-Time Control, High-Speed I/O)

Recommended Approach: Bare-metal is preferred.

Rationale: When systems require low latency and precise timing, HAL’s overhead and abstractions can cause issues. Bare-metal programming ensures direct access to hardware, which is necessary for optimal performance.

Key Factors:

• Low Latency: Bare-metal eliminates the overhead introduced by HAL.
• Resource Efficiency: Direct hardware access optimizes memory and CPU usage.
• Deterministic Behavior: Essential for real-time applications.