Embedded System Design Patterns and Best Practices

Embedded System Design Patterns and Best Practices

In the complex and critical field of embedded system design, design patterns and best practices shine like a beacon, serving as the core elements that ensure the system possesses high reliability, excellent efficiency, and good maintainability. The following will elaborate on the key points involved in the design patterns and best practices in the embedded system design process:

1. Real-time System Design

Real-time systems are an indispensable part of embedded systems, occupying a unique position. These systems have strict requirements that must accurately meet the timeliness constraints to ensure the correctness of the entire system. Real-time systems can be further divided into “hard” real-time systems and “soft” real-time systems based on their sensitivity to time. For “hard” real-time systems, time is an absolute constraint, and each task must be completed within the specified time limit; any delay may lead to severe system failures or even crashes. In contrast, “soft” real-time systems are relatively flexible, introducing other metrics such as average response time and task completion priority to evaluate whether the system meets requirements.

2. Embedded Design Constraints

One of the significant characteristics of embedded system design is that it faces numerous strict constraints. Reliability is paramount, meaning the system must stably execute its functions during long-term operation without being affected by external disturbances and internal failures. Robustness requires the system to maintain normal operation or degrade gracefully in the event of abnormal situations, such as inputting abnormal data or hardware failures, rather than crashing directly. Security involves protecting data, preventing unauthorized access, and avoiding harm to personnel and the environment in critical application scenarios. These constraints intertwine, establishing strict boundaries for embedded system design.

3. Operating System Selection

In the vast world of embedded systems, developers have diverse choices regarding operating systems. They can opt for traditional operating systems (OS), real-time operating systems (RTOS) designed specifically for real-time applications, or even choose a bare-metal implementation. RTOS demonstrates unique advantages in real-time and embedded application scenarios by scheduling tasks based on priority. This priority-based scheduling mechanism ensures that high-priority critical tasks are processed promptly, thereby guaranteeing the system’s real-time performance. For example, in embedded systems in the aerospace field, tasks related to flight control are assigned high priority to ensure stable flight.

4. Embedded Middleware

The development of embedded systems is a complex process that closely collaborates with hardware. In this process, hardware and software are interdependent, and any minor hardware change can trigger significant changes in software architecture, akin to the butterfly effect. Embedded middleware plays a crucial role as a bridge between hardware and software, effectively reducing this coupling, minimizing the impact of hardware changes on software, and facilitating software updates and maintenance.

5. Debugging and Testing

In the arduous journey of embedded system development, debugging on specified hardware is undoubtedly a challenging peak. This is because the hardware environment of embedded systems is often quite special, differing significantly from ordinary computer systems, posing huge challenges for debugging. Test-driven development (TDD), an agile practice, provides a powerful tool to address this issue. By writing test cases first during the development process, developers can gain a clearer understanding of software functional requirements and expected behaviors, thereby improving software quality. For instance, in the development of automotive electronic control systems, TDD can help developers promptly identify and fix potential software vulnerabilities, ensuring the safety of vehicle operation.

6. Hardware Access Concepts

Embedded systems are closely linked to hardware and must be able to access hardware directly. Hardware in embedded systems can be roughly categorized into four major types: infrastructure hardware, such as power supply modules, which provide basic support for the entire system; communication hardware, including various communication interfaces and protocol chips, responsible for data exchange between the system and external devices; sensor hardware, such as temperature and pressure sensors, which can sense changes in the external environment and convert these physical quantities into electrical signals for system processing; and actuator hardware, such as motors and valves, which act on the external environment based on system instructions. This classification of hardware helps developers better understand and design hardware access mechanisms.

7. Design Patterns

In the design landscape of embedded systems, several design patterns have been validated through long-term practice and proven to be highly valuable. For example, the hardware proxy pattern provides a unified access interface for hardware resources, hiding the complex details of hardware, making it easier for the software to utilize hardware functions. The hardware adapter pattern builds a bridge between different hardware platforms, enabling software to operate normally across various hardware configurations. The mediator pattern introduces a mediator object to coordinate interactions between multiple hardware or software modules, reducing their coupling. The observer pattern handles one-to-many dependencies between objects in the system, allowing dependent objects to automatically receive notifications and respond accordingly when the state of one object changes. Debouncing and interrupt patterns play crucial roles in handling hardware signal jitter and efficiently responding to hardware interrupts, ensuring the system can accurately capture and process critical signals.

8. Hardware/Firmware Interface Design

The book “Hardware/Firmware Interface Design: Best Practices for Improving Embedded System Development Efficiency” serves as a treasure trove, providing us with rich principles and best practices for optimizing hardware/firmware interfaces. It covers critical content such as register layout, where a reasonable register layout can enhance the efficiency and accuracy of hardware access. The design of interrupt mechanisms is also crucial, determining how the system responds to hardware interrupt requests to ensure timely processing of important events. Timing and performance considerations involve the timing of data transfer between hardware and firmware, instruction execution order, and other factors that directly affect the overall system performance. Additionally, abort and error handling mechanisms ensure that the system can take appropriate measures in the event of abnormal situations, such as hardware failures or firmware execution errors, to avoid system crashes or data loss.

9. Development Models

There are various development models for embedded system design, each with its unique characteristics and applicable scenarios. The waterfall model, with its phased and sequential nature, can systematically advance the development process in projects with clear and stable requirements. The prototype model allows for the rapid construction of a runnable prototype system, enabling users to experience and provide feedback early, thus continuously improving the system. The iterative model permits multiple repetitions of certain stages during development to gradually enhance system functionality. Agile development emphasizes rapid responsiveness to changes, teamwork, and customer satisfaction, making it suitable for projects with changing requirements. Model-driven development guides the development process by establishing system models, raising the abstraction level of development. Component-based development decomposes the system into multiple reusable components, improving development efficiency and system maintainability.

10. OS-less Embedded System Software

For embedded systems that do not use an operating system, an effective best design approach is to carefully segment the software into multiple sub-functions or sub-businesses, writing corresponding subprograms for each sub-function. Then, these functional subprograms are sequentially called in an infinite loop. This design approach can effectively manage system resources and execute tasks without an operating system. For example, in some simple electronic devices, such as small remote control embedded systems, this method can achieve stable and efficient functionality.

In summary, these rich and diverse design patterns and best practices build a solid theoretical foundation for embedded system design, while also playing an indispensable guiding role in practice, greatly assisting developers in improving development efficiency and enhancing the overall system performance, pushing embedded systems towards a more stable and efficient direction.