Maddy Osman For every software development project you have, early decisions matter. The approach you take from the start can have a significant ripple effect on the overall performance, efficiency, and scalability of your final deliverable. This is especially true when you’re dealing with embedded systems projects that have strict requirements around efficiency and quick response rates.
Two main approaches for embedded systems are bare metal and RTOS. Both bare metal and RTOS can provide the streamlined performance you need, but they each have their own strengths and limitations. For instance, RTOS introduces an operating system (OS) layer that may consume more resources but provides more structure and built-in services. A bare metal environment, on the other hand, has no OS-induced overhead and gives you the benefits of direct control over your hardware.
So, which one is best? In this article, we’ll examine how both approaches work and explore their tradeoffs so you can make confident decisions about your embedded systems projects.
Here’s a look at what you’ll learn in this comprehensive guide to choosing the best approach for your embedded systems projects.
- The growing importance of embedded systems
- Understanding RTOS
- Understanding bare metal programming
- Bare metal vs RTOS for embedded systems
- Choosing between bare metal vs RTOS
- Final thoughts: Bare metal vs RTOS — Choose the right option
Key points
- Embedded systems development projects are becoming more common because they’re essential for powering a wide range of cutting-edge products, from hybrid cars to patient monitoring devices.
- For software developers, two of the most common approaches for embedded systems are bare metal and RTOS.
- The bare metal approach has the benefit of direct hardware control and minimal overhead, while RTOS comes with a light abstraction layer that helps automate more complex tasks but tends to use up more resources.
The growing importance of embedded systems
Embedded systems are on the rise. This is mainly because they are integral elements of several modern technologies, including the Internet of Things (IoT). From 2023 to 2032, Global Market Insights predicts that the embedded systems market will grow from $110.3 billion to $190 billion.
You might be surprised to discover just how many industries rely on embedded systems. You can find them in products like hybrid cars, entertainment systems, factory robots, and monitoring systems.
One quality that’s often required of these embedded systems products is that they complete tasks in real time. For example, when you give a factory robot a command, you want it to execute right away.
Not to mention, for many of these products, such as patient monitoring systems or air traffic control, the cost of mistakes or delays in response time can be high. As such, these systems need to have a software foundation that’s exceptionally efficient and reliable. So, it’s crucial to find a development approach that can meet these unique needs.
As commercial and consumer demand for embedded systems rises, they’ll create many great opportunities for software development projects. If you want to make the most of them, it’s essential to start off on the right foot by choosing the most appropriate approach for the final product or application.
Often, you’ll be choosing between using bare metal programming or relying on an RTOS. In this guide, we’ll look at each option and its trade offs so you can confidently make the best decisions for each project.
Understanding RTOS
RTOS stands for real-time operating system. As the name implies, it’s often used for real-time applications because it’s more lightweight than a traditional OS.
Compared to a general-purpose OS like Windows or Linux, RTOS offers fewer built-in services, but that means it’s more streamlined. Its superpower lies in its ability to enable deterministic scheduling, which gives you the predictability and fast response times you need for real-time applications.
Deterministic scheduling means that you’ll get the same output whenever you repeat an input, thus providing predictability. Specifically, it means that the execution order and task time remain consistent for each input.
This is different from the non-deterministic scheduling used by traditional OS solutions. In those cases, factors like CPU upload and resource availability can change which processes get run, meaning the same input can have different outputs and response times.
The most popular RTOS solutions include FreeRTOS, SAFERTOS®, and VxWorks.
Advantages of the RTOS approach for an embedded systems project:
- Multitasking support
- Inter-task communication
- Task prioritization
- Real-time performance
- Scalable modular design
Disadvantages of the RTOS approach for an embedded systems project:
- OS learning curve
- Higher overhead
- Additional resource consumption
Understanding bare metal programming
Bare metal programming refers to the process of writing software that runs directly on a system’s hardware. There’s no abstraction layer like a device driver or operating system, meaning you’re essentially removing a middleman and creating more efficiency.
Because you have direct hardware access, you get precise control and optimal resource management.
One of the best things about bare metal programming is there’s no OS-induced overhead. That said, when there’s no OS handling operations, the management of memory, interrupts, peripherals, and hardware initialization become the developer’s responsibility.
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Advantages of the bare metal approach in embedded systems:
- Lower resource consumption
- Higher ability to customize
- Direct hardware control
- Minimal latency
- Less overhead
Disadvantages of the bare metal approach in embedded systems:
- Increased developmental complexity for larger projects
- Lack of built-in services
- Limited multitasking
- Difficulty scaling
Bare metal vs RTOS for embedded systems
The efficiency you get from bare metal programming and RTOS-based software engineering are both well-suited for embedded systems. Ultimately, the choice of which approach to use comes down to whether or not you need the OS. Let’s look at how each of these options impacts different aspects of a development project.
Multitasking
One requirement you’ll see in many embedded systems projects is efficient multitasking. Bare metal and RTOS can both accomplish these, but they do it differently.
In bare metal programming, cooperative and task interruption approaches are often used for multitasking. While these can work well for a smaller number of tasks, manual resource management can become overwhelming as your project scales. Another major challenge is the lack of a built-in scheduler to enable preemption, which can lead to delays in response times.
With RTOSes, you have the benefit of preemptive scheduling, which lets you offload task management and multitasking to the OS. Furthermore, an RTOS is excellent for facilitating inter-task communication with tools like semaphores, message queues, and event flags. These built-in services are helpful if you want to maintain efficiency as you scale a project.
Resource constraint
While RTOS and bare metal are more efficient than a traditional OS, they differ in terms of resource usage and power consumption.
Typically, a bare metal environment uses up fewer resources than an RTOS because there’s no abstraction layer running in the background. The direct control you get with bare metal also gives you the opportunity to optimize code paths and manage the power modes of microcontrollers to ensure maximum efficiency and minimal waste.
With an RTOS, you have significantly less control over the system. Not to mention, there’s often a minimum amount of memory needed to load and maintain the operating system. Compared to bare metal, RTOS generally consumes more memory and processing power. If you’re dealing with a highly constrained environment, an RTOS may not be the best fit.
Development complexity
Differences in developmental complexity between RTOS and bare metal approaches boil down to the presence (or absence) of an operating system.
The bare metal approach does not use an operating system, which gives developers direct control over the hardware. As such, you can tailor the software to maximize hardware resources and lower your overall footprint, which is crucial for many embedded systems.
The downside of bare metal programming happens when projects scale or require more functions. For instance, functions like task scheduling and memory management that are built into an OS will need to be created using bare metal code from scratch.
With an RTOS project, the OS provides a basic level of structure and built-in functionality. For smaller projects, an OS can mean added complexity, but the structure and services it offers can help simplify larger projects. Another disadvantage of an RTOS here is the initial learning curve required for the system and its API, which can lead to a longer development time and more challenges with debugging code.
Real-time capabilities
RTOS and bare metal programming can both meet real-time requirements, but they differ in how they handle response times at different levels of project complexity.
With bare metal systems, the lack of an OS allows for efficiency and quick response times. In particular, you don’t have to worry about OS-induced overhead or context switching. As long as your code is efficient, you can expect fast responses and consistent outputs.
The absence of the OS layer means that bare metal is a manually managed environment. This has two key disadvantages in terms of real-time capabilities. First, it becomes increasingly difficult to maintain real-time response rates as projects scale. Second, unexpected delays can happen if developers don’t manage interrupts well.
With an RTOS, on the other hand, you don’t have to worry as much about manual task management because the OS handles timing, scheduling, and interrupts. That said, the presence of an OS (even if it’s lightweight) does introduce some overhead.
Security
Security is crucial for many embedded systems, such as those used in patient monitoring, advanced automobiles, and consumer devices. Safeguarding these applications helps protect against cyber threats, maintain reliability, and comply with industry regulations. As such, it’s important to understand the implications each approach has regarding security.
With bare metal programming, the direct control allows developers to tailor security measures to the hardware. This environment also has a lower attack surface due to the lack of an abstraction layer. Still, implementing the necessary security precautions can become more challenging as projects grow in size.
For larger projects, built-in security services offered by an RTOS become an advantage. Most RTOSes come with a comprehensive set of features such as memory protection and user and kernel modes.
Choosing between bare metal vs RTOS
At the end of the day, the right approach can lead to a smoother and more successful embedded systems project, while the wrong one can lead to complications, timeline delays, and performance issues.
When choosing which way to go about an embedded system software design, you need to look at the unique needs of each project. In particular, look at the overall complexity, level of scale, resource availability, and timing requirements.
In general, bare metal is a great choice for straightforward projects and highly-constrained environments. RTOS, on the other hand, is more appropriate when you’re working on a more complex project or need to scale in the future. Because of their unique tradeoffs, bare metal and RTOS are employed in different types of projects.
Bare metal use cases include:
- Digital signal processing (DSP) systems
- Microcontroller-based appliances
- Low-power IoT sensors
- Real-time controllers
RTOS use cases include:
- Consumer electronics like smartphones and tablets
- Advanced automotive systems
- Patient monitoring systems
- Industrial automation
- IoT gateways
Final thoughts: Bare metal vs RTOS — Choose the right option
Both bare metal and RTOS are capable of meeting the efficiency requirements of embedded systems projects. That said, they offer different benefits and present contrasting challenges. Figuring out the best approach involves understanding the tradeoffs and how they impact the needs and goals of each project.
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