The Pros and Cons of RTOS vs Bare Metal: Which Will You Choose?

When developing embedded systems, developers have two options: using a Real-Time Operating System (RTOS) or programming directly on the hardware, also known as bare metal programming. Both approaches have their advantages and disadvantages, and choosing between them depends on various factors such as the system’s complexity, performance requirements, and available resources. This article discusses the pros and cons of using an RTOS versus bare metal programming.

What is an RTOS?

An RTOS is a software layer that runs on top of the hardware and provides scheduling, resource management, and inter-task communication services. The primary purpose of an RTOS is to enable the development of complex, real-time applications that require deterministic behavior, low latency, and high reliability. An RTOS achieves this by providing a framework for developers to organize their code into independent, concurrently executing tasks that can communicate with each other and access shared resources in a controlled and predictable manner.

Pros of using an RTOS

1. Task Management: One of the significant advantages of using an RTOS is that it provides a task management system that simplifies the development of complex applications. The RTOS handles the scheduling of tasks, ensuring that they execute in a predictable and deterministic manner. Tasks can be created, deleted, and suspended, and their priority can be changed at runtime. This flexibility enables developers to design applications that can handle multiple concurrent tasks and respond quickly to changing system conditions.
2. Resource Management: An RTOS provides a mechanism for managing system resources such as memory, I/O, and peripherals. The RTOS ensures that resources are allocated and released in a controlled and predictable manner, preventing resource conflicts and improving system reliability. The RTOS also provides mechanisms for inter-task communication and synchronization, enabling tasks to share resources and coordinate their activities.
3. Modularity: An RTOS encourages the development of modular code, where different parts of the system are encapsulated in separate tasks. This modularity makes it easier to maintain and extend the system and improves code reusability. Developers can add new functionality to the system by creating new tasks without disrupting the existing tasks.
4. Debugging: Debugging an RTOS-based application is easier than debugging bare metal code. An RTOS provides visibility into the system’s internal state, including task scheduling, resource allocation, and inter-task communication. Developers can use this information to diagnose system problems and optimize system performance.

Cons of using an RTOS

1. Overhead: An RTOS introduces overhead into the system, which can reduce performance and increase memory usage. The RTOS must manage the scheduling of tasks, allocate and release system resources, and provide inter-task communication services, all of which require CPU cycles and memory. On smaller RTOS’s this overhead may be small enough not to matter.
2. Complexity: An RTOS introduces complexity into the system, which can make it harder to understand and debug. Developers must be familiar with the RTOS API and understand how tasks, resources, and inter-task communication work. This knowledge can take time to acquire, increasing development time and cost.
3. Cost: Using an RTOS can increase the cost of the system. Many commercial RTOS vendors charge licensing fees, which can be expensive for small projects. Additionally, an RTOS requires more memory and processing power than bare metal programming, which can increase the hardware cost of the system.

What is bare metal programming?

Bare metal programming is the practice of programming directly on the hardware, without the use of an operating system or middleware. In this approach, developers write code that interacts directly with the hardware, accessing registers and memory locations to control system behavior. Bare metal programming is typically used for low-level tasks, such as device driver development and hardware initialization.

Pros of bare metal programming

1. Performance: Bare metal programming can provide better performance than an RTOS because there is no overhead from an operating system. Developers have direct control over the hardware, allowing them to optimize code for specific hardware features and reduce processing time. This approach is especially useful in applications where speed and real-time response are critical.
2. Efficiency: Bare metal programming can be more efficient than using an RTOS in terms of memory usage. The absence of an operating system eliminates the overhead associated with managing system resources, resulting in a smaller code footprint and lower memory usage. This approach is useful in applications with limited memory resources.
3. Simplicity: Bare metal programming is simpler than using an RTOS because developers have complete control over the system. There is no need to learn an RTOS API or understand the complexities of task management and resource allocation. This approach is useful in applications where code size and complexity need to be minimized.

Cons of bare metal programming

1. Lack of abstraction: Bare metal programming requires developers to interact directly with the hardware, which can be challenging and error-prone. Developers must understand the hardware’s specific features and limitations and write code that takes advantage of those features while avoiding potential pitfalls. This approach can be time-consuming and increase the risk of errors.
2. Limited scalability: Bare metal programming is not scalable, which can make it difficult to develop complex applications. As the system becomes more complex, the code becomes harder to manage and maintain. This approach is useful in applications with relatively simple requirements, but it is not suitable for more complex systems.
3. Debugging: Debugging bare metal code can be challenging because there is no abstraction layer between the code and the hardware. Developers must rely on low-level debugging techniques, such as hardware breakpoints and memory dumps, which can be time-consuming and difficult to use.

Comparison between an RTOS and bare metal programming

1. Performance: Bare metal programming can provide better performance than an RTOS because there is no overhead from an operating system. However, an RTOS can still provide high performance overall, especially in complex applications with real-time requirements.
2. Complexity: Using an RTOS introduces complexity into the system, which can make it harder to understand and debug. Bare metal programming is simpler, but it requires developers to interact directly with the hardware, which can be challenging and error-prone.
3. Scalability: An RTOS is more scalable than bare metal programming, making it easier to develop and maintain complex applications. Bare metal programming is suitable for relatively simple systems but can become unwieldy in more complex applications.
4. Modularity: An RTOS encourages modularity, which makes it easier to maintain and extend the system. Bare metal programming requires developers to manage the system’s complexity manually, which can make it harder to maintain and extend.
5. Debugging: Debugging an RTOS-based application is easier than debugging bare metal code because the RTOS provides visibility into the system’s internal state. Bare metal programming requires developers to rely on low-level debugging techniques, which can be time-consuming and challenging to use.
6. Cost: Using an RTOS can increase the cost of the system, especially if commercial RTOS vendors charge licensing fees. Bare metal programming can be more cost-effective, but it may require more hardware resources and deeper technical skills which can increase the project costs.

The choice between using an RTOS and bare metal programming depends on various factors, including performance requirements, system complexity, and available resources. An RTOS provides task management, resource allocation, and inter-task communication services, making it easier to develop complex, real-time applications. However, an RTOS introduces complexity and overhead into the system, which can increase development time and cost. Bare metal programming is simpler and more efficient but requires developers to interact directly with the hardware, which can be challenging and error-prone. Ultimately, the choice between an RTOS and bare metal programming depends on the specific requirements of the system and the resources