How do we choose the most suitable real-time operating system?
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How do we choose the most suitable real-time operating system?

Posted Date: 2024-02-01

Real-time operating system (RTOS) has entered more than 50% of embedded projects. RTOS can help us manage system timing, resources, memory, etc. They provide us with tools for efficient scheduling, such as time slicing and thread preemption, while simplifying inter-task communication.

As more teams move to 32-bit microcontrollers and continue to adopt IoT technologies, the need for RTOS will only continue to grow. If you are transitioning to an RTOS or have done so recently, you know that choosing an RTOS can be a significant challenge. So, how to choose RTOS?

Avoid common selection mistakes

There are several common mistakes we should avoid when choosing an RTOS.

First, it's not uncommon for teams to immediately rule out the option of using a commercial RTOS. With so many open source RTOS available, why would anyone pursue a commercial RTOS? The reasons usually come down to considerations such as certification, quality, security, and support. For these reasons, commercial RTOSs should not be ruled out immediately.

Secondly, don't choose your silicon vendor as your RTOS just because it is directly supported by it. While this support is often encouraging, you'll find that they often lag behind the latest versions of RTOS. In this case, we may not be able to get critical security updates as quickly as if we had direct access to the source.

Finally, don't choose an RTOS just because it's currently popular. Over the course of my career, I have seen many trends come and go. In some cases, they vary by years, or even less. Technology loves shiny new toys, but if you're building a product that requires years of support, you may not be able to adopt trendy, unproven solutions.

The right way to choose RTOS

Choosing an RTOS should be an engineering pursuit. This means choosing in a scientific, engineering-focused way. Start by identifying the key functionality required in the RTOS. It could be performance, code size, security features, etc. It’s best to make a list first.

Next, look at your list and give it a numerical value based on its importance. For example, if licensing costs are important, you could list it as 5. If licensing costs are not important, specify 1 or even 0. By ranking in this way, you can understand which factors are essential to the selection process. It tells us what functions and features we want the RTOS to have. After all, no two RTOSs are exactly the same, or provide the same functionality in the same way.

Only after the feature list has been identified and sorted can we evaluate which RTOS is suitable for our application. Each developer's own biases may influence the selection process. I usually recommend that teams use the KT matrix to perform assessments. Each developer can rate how well each RTOS under consideration matches the list of required features. They can provide a rating between 0–5, which can then be used together with the feature ranking to generate a weighted value. The weighted sum of features can be used to compare how well each RTOS meets the application's needs.

This enables an unbiased decision to be made to select an RTOS that fits the needs of the team. We may find that, depending on our application, more than one RTOS is suitable. When this happens, we can then choose which system to use based on personal preference.

in conclusion

Choosing an RTOS that will work with our application and continue to perform well for the foreseeable future is no easy task. It's not uncommon to select an RTOS, only to discover months or quarters later that it doesn't quite meet our expectations. As we've seen, it's crucial to spend a little more time upfront and determine what we expect from the RTOS. After we understand our needs, we can carefully evaluate which RTOS best meets the application needs.

Only in this way can we truly be satisfied with our choice of RTOS. If you choose the trendiest, most popular, or vendor-direct RTOS, you may find that your future development efforts are a bit bumpy.


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