Transform Your Embedded Software Architecture with These Powerful Practices

Traditional embedded software architecture has been monolithic designs that tightly couple the application code to the hardware. As many learned during the COVID microcontroller shortage, there are many disadvantages to this type of architecture. There is a better way!

If you’re struggling to adapt your embedded system to new requirements or finding that adding features is becoming increasingly complex and risky, you need to modernize your embedded software architecture.

In this post, we’ll explore how to adopt modern architectural practices to help you meet your companies and customers’ evolving needs.

Let’s explore modern software architecture and how to apply it to your systems.

Note: If you’re unsure why you need an embedded software architecture, check out my post: 5 Reasons to Develop a Software Architecture.

The Cost of Architectural Debt

Many embedded systems suffer from what we call “architectural debt“—design decisions made years ago that now restrict innovation, complicate testing, and slow development. This debt manifests as:

• Tightly coupled components that can’t be modified independently
• Hardware-dependent software that’s difficult to test
• Monolithic codebases that are challenging to understand and maintain
• Feature implementations that cross-cut through multiple system layers

The result? Slower development cycles, increased bugs, difficulty onboarding new team members, and ultimately, products that can’t keep pace with market demands.

Shifting to Modern Embedded Software Architecture Thinking

When you stop to think about software architecture, the first thing you probably think about is software diagrams that show the structure of the software. While software diagrams certainly are a critical piece of the software architecture process, they are only the tip of the iceberg.

Over time, the definition of software architecture has evolved as the software industry has matured. One of my favorite definitions is from the now-deprecated IEEE 1471:

“A software architecture is the fundamental organization of a system embodied in its components, their relationship to each other and the environment, and the principles guiding its design and evolution.”

While this is a great definition, it’s strictly focused on the structural aspects of the system and only hints that there is more to architecture than meets the eye!

Software architecture isn’t just about the structure, it’s also about the trade-offs, and the principles that make the architecture.

A modern embedded software architecture should at least cover these four critical points:

1. Software characteristics that the software system must exhibit
2. Principles and philosophies, the rules that are used to make decisions about the architecture
3. Decisions and the trade-offs that are made when designing the architecture.
4. Structure and the styles are used to define the organization of the software.

I like to look at these four points as pieces in the software architecture puzzle as shown below:

Most embedded software architectures barely document the structure of the software, let alone the other three pieces. However, if you want a modern, scalable, and flexible embedded software architecture, you must ensure that you don’t neglect these other areas.

Let’s look at these areas and how they can impact your development.

Identifying Embedded Software Architecture Characteristics

It’s crucial to understand what characteristics your software needs to exhibit. These characteristics should drive your architectural decisions and serve as evaluation criteria for your design choices.

Software characteristics are often defined by the “ilities” your software must exhibit. For example:

• Portability
• Scalability
• Flexibility
• Reliability
• Reusability
• Etc

In “Building Evolutionary Architectures”, the first chapter defines dozens of these “ilities” that software systems might need to exhibit.

Explicitly documenting these “ilities” and prioritizing them based on your specific application domain can help you focus on the most critical characteristics your software architecture needs to exhibit.

Note: I often will call these “ilities” software qualities or attributes.

If you’re unsure how to get started with this analysis, you can download my Software Architecture Characteristics Prioritization Worksheet. It’ll walk you through a simple process to identify the most critical characteristics for your software system.

Remember, while there are more than 70 different ilities, you want to identify just the top five most important ones that will drive your architectural principles and decisions. Focusing on more than that will compromise your architecture by having it try to do too much!

Defining Embedded Software Architecture Guiding Principles

Architectural guiding principles serve as a decision-making framework for your team. They represent the “rules of the road” that all design decisions must follow, ensuring consistency across the system even as it evolves.

Over a typical development cycle, losing sight of what is guiding your decisions is easy. Development cycles can decay into a firefighting effort where every developer has their head down and works furiously to deliver the project.

Getting things done is great, but not at the cost of high technical debt that cripples future development efforts. Documenting guiding principles helps to ensure that everyone knows the rules for development.

For embedded software systems, a few examples of powerful guiding principles include:

• Data dictates design: Focus on data flows first, then build processing elements around them
• There is no hardware, only data: No application code should directly interact with hardware registers or memory (design from the top down)
• Component isolation: Each module should have a single responsibility and well-defined interfaces
• Test-driven development: All components must be designed for automated testing
• Practical beats perfect: Focus on practical implementations, and don’t let perfection get in the way of delivering software.

Your development team should document, share, and reinforce the most essential principles of your software. They become the foundation upon which all architectural decisions are built and ensure that no one can conveniently forget the rules of the software.

Embedded Software Architecture Decisions and ADRs

One of the most significant shifts in modern architectural practice is the recognition that architecture evolves through a series of decisions, each with its own context, constraints, and tradeoffs.

Architecture Decision Records (ADRs) provide a structured way to document these critical decisions. For example, check out the following ADR for adopting message queues for inter-task communication:

# ADR-001: Adopt Message Queue for Inter-Task Communication

## Context

Our current direct function call approach between tasks is creating tight coupling and making unit testing difficult. We need a communication mechanism that isolates components and supports asynchronous operations.

## Decision

We will implement a message queue system for all inter-task communication, with standardized message formats and priority levels.

## Consequences

- Positive: Components can be tested in isolation

- Positive: Asynchronous processing becomes possible

- Positive: New components can be added without modifying existing ones

- Negative: May introduce additional memory overhead

- Negative: Could add latency to critical operations

## Compliance Verification

All inter-task communications will be reviewed during code reviews to ensure they use the message queue system.

The benefits of ADRs cannot be overstated:

• They create a decision history that explains why the system is designed the way it is
• They explicitly document tradeoffs, acknowledging that every decision has both benefits and drawbacks
• They provide context for future modifications, helping new team members understand the rationale behind existing designs
• They prevent the same architectural debates from recurring repeatedly

I can’t tell you how many times I’ve had a new engineer join the project, and in their great wisdom tell us how everything we are doing is wrong. After pointing them to the ADRs and telling them to read, it’s funny how quickly they understand what decisions were made and why and suddenly our existing software is brilliant!

ADRs maintain a valuable history of what trade-offs were made and why and explain how your system evolved.

Modern Embedded Software Architecture Styles

Embedded software architecture has evolved significantly beyond the traditional monolithic approach. While many systems today use some level of layering to try to separate the system into more reusable parts, there are many more architectural styles and patterns that can be applied to embedded systems.

Let’s look at a few architectural patterns worth considering.

Service-Based Architecture

In this model, your system comprises independent services responsible for a specific domain function. Services communicate through well-defined interfaces, typically using message passing rather than direct function calls.

This approach:

• Allows services to be developed and tested independently
• Makes it easier to replace or upgrade individual services
• Supports parallel development by different team members or teams

Microkernel Architecture

A microkernel architecture separates core system functionality (the kernel) from extended services. This pattern is particularly valuable for embedded systems where reliability is critical.

Benefits include:

• The minimal kernel is easier to verify and validate
• Services can be started, stopped, or replaced without rebooting
• Hardware-specific code can be isolated from application logic

Layered Architecture with Clean Interfaces

While layered architectures are standard, modern implementations focus on clean interfaces between layers with dependency rules that flow in only one direction.

For example, a four-layer approach might include:

1. Hardware Abstraction Layer: Isolates hardware-specific code
2. Platform Services Layer: Provides OS abstractions and core utilities
3. Domain Layer: Implements application-specific business logic
4. Application Layer: Manages workflows and external interfaces

Each layer should only depend on the layer directly beneath it, and interfaces should be abstracted through dependency inversion where appropriate.

Documenting your Architecture with 4C and Data-Driven Design

Modern embedded software architecture benefits enormously from two complementary approaches: the 4C modeling method and data-driven design.

4C modeling is a process that can help you diagram your software consistently in a way that naturally flows from the most generic level (what I call the 37,000-foot view) all the way down to the detailed class diagrams used to implement the code.

Data-driven design can be used independently or augment the 4C modeling method. The idea here is that we first identify the data assets in our system and then trace how they are generated and flow through the system.

Let’s look at these in a little more detail.

The 4C Model for System Visualization

The 4C model provides a way to visualize your system at four increasingly detailed levels:

1. Context: How your system relates to users and external systems
2. Containers: The high-level technical building blocks of your system
3. Components: The logical components inside each container
4. Code: The implementation classes and relationships

This hierarchical approach allows stakeholders to understand the system at the level of detail most relevant to them and helps ensure that implementation decisions align with architectural intent.

In many cases this model allows architects and developers to work closely together. An architect will often live in the Context, Container, and Components diagrams. However, they must carefully coordinate with developers on the Code (class) diagrams.

The developers often have a better understanding of the implementation, so that careful coordination can ensure that the architecture isn’t just a pretty picture, but something that reliably represents the embedded software system.

Data-Driven Design: There Is No Hardware, Only Data

Perhaps the most transformative shift in embedded thinking is moving from a hardware-centric to a data-centric mindset. We often say, “There is no hardware, only data.”

This principle recognizes that hardware elements—sensors, actuators, and peripherals—are fundamentally just data sources and sinks. By focusing on data flows first, you:

• Isolate hardware specifics behind clean data interfaces (See 5 Tips for Designing an Interface in C)
• Can simulate inputs and outputs for testing
• Design around the information needed, not the hardware providing it
• Create systems that can adapt when hardware changes
• Enable hardware/software co-design rather than sequential development

This approach leads to architectures where data schemas and transformations become first-class design elements, with hardware interactions pushed to the system’s edges.

That doesn’t mean that we ignore the hardware. It’s still an important part of any embedded system, but it allows us to architect our system to work on any hardware platform and start not just the design but also the implementation long before the hardware team is able to provide us with prototypes.

Enabling Long-Term Flexibility

The ultimate measure of architectural quality is how well it supports change over time. While many systems might be one off products, there is a growing number of teams that are developing what I call platform systems.

These are embedded software systems that will be used and supported for a decade or more to support multiple product lines and customers. While these have always existed, the number of teams engaging in this type of development has grown considerably over the last 20 years.

Because of these changes, what a software architecture provides has changed.

A modern embedded architecture provides:

• Flexibility: The ability to modify one component without affecting others
• Scalability: The capacity to handle growing requirements and expand functionality
• Testability: The ease with which components can be verified in isolation
• Adoptability: The capability to incorporate new technologies and techniques

Your modern build system (from Step 1) directly enables this architectural flexibility by:

• Supporting conditional compilation for feature variants
• Enabling different build targets for testing vs. production
• Managing dependencies between components
• Facilitating continuous integration and testing
• Providing configuration mechanisms that support architectural boundaries

As you’ll see throughout this paper, each piece of the 7-Step process is interrelated. While they can be implemented separately, they build on each other to help you create modern embedded software that helps you deliver faster.

Self-Assessment Checklist

Rate your current architectural approach against these modern practices. Simply place a check next to each if you are currently following this practice:

• We have documented software characteristics and prioritized them
• We have established architectural guiding principles
• We document architectural decisions with their context and tradeoffs
• Our system uses clear component boundaries with well-defined interfaces
• Our architecture separates hardware-specific from application code
• We design around data flows rather than hardware interactions
• We can test most components without hardware

Scoring:

• 0-2 checks: Legacy Architecture – Immediate modernization needed
• 3-4 checks: Transitional Architecture – Significant improvements possible
• 5-7 checks: Modern Architecture – You’re ahead of the curve

Your Next Steps

Architecture isn’t something you create once and then implement—it’s a continuous practice of making intentional design decisions that allow your system to evolve gracefully over time. By embracing these modern architectural approaches, you’ll build embedded systems that remain adaptable, maintainable, and competitive for years to come.

Some additional next steps you might consider taking after reading this post include:

1. Document your current architecture using the 4C model
2. Identify the most painful architectural limitations
3. Create guiding principles for future development
4. Start documenting new architectural decisions as ADRs
5. Implement a hardware abstraction layer if you don’t have one
6. Define clear data models for your system’s information flows
7. Use the characteristics worksheet to identify your software characteristics

Pro Tip: Don’t attempt to refactor everything at once. Start with the most problematic areas and gradually transform your architecture as you add new features.

If you find that you’re stuck and need guidance, feel free to contact me at [email protected]!

Happy Coding!