STM32 in Medical Device Development: What You Need to Know
The STM32 family is one of the most capable and cost-effective choices for medical device firmware — but using it in a regulated product requires more than just writing good code.
ST Microelectronics' STM32 family has become a go-to platform for embedded engineers across industries, and for good reason. The devices offer an exceptional combination of processing power, peripheral depth, power efficiency, and toolchain maturity. At SiGenix, we have used STM32 microcontrollers in multiple FDA-regulated medical devices — and in this article we want to share what that experience has taught us.
Why STM32 Works Well in Medical Applications
Medical devices place demands on a microcontroller that consumer products simply do not. You need deterministic timing for safety-critical control loops, sufficient processing headroom for signal processing and communication stacks running simultaneously, low-power modes for battery-operated devices, and a long product lifecycle with guaranteed supply.
The STM32 family checks all of these boxes. The L-series devices (STM32L4, STM32L5) are purpose-built for ultra-low-power applications — ideal for wearable monitors and implant-adjacent devices. The H-series (STM32H7) brings Cortex-M7 performance at clock speeds up to 550 MHz, making it suitable for real-time signal processing in diagnostic equipment. And ST has a strong track record of maintaining long-term availability, which matters enormously when you are planning a product that will be in the field for ten or fifteen years.
IEC 62304 and What It Means for Your Firmware
If your device is FDA-regulated, your software must be developed under IEC 62304 — the international standard for medical device software lifecycle processes. This standard does not tell you how to write code. What it does require is that you have a documented and repeatable process for everything you do: requirements, architecture, unit testing, integration testing, anomaly tracking, and change control.
In practice, this means every function in your STM32 firmware needs a traceable requirement behind it. It means your test cases need to be written before the code is reviewed, not after. It means when a bug is found in the field, you have a formal process for assessing its impact, documenting the fix, and re-verifying the affected software units.
None of this changes how you write C code for an STM32. It changes how you manage the work around that code.
Choosing the Right RTOS
Most medical device firmware of any complexity benefits from a real-time operating system. FreeRTOS is the most common choice on STM32 — it is well-documented, widely understood, and ST provides native integration through their STM32CubeIDE toolchain. For IEC 62304 Class C software (the highest safety classification), some teams prefer SAFERTOS, which is a pre-certified variant of FreeRTOS with additional documentation artifacts included.
Whatever RTOS you choose, the key discipline is task prioritization and stack sizing. We have seen more than one medical device ship with stack overflows that only manifested under specific load conditions in the field. Static analysis tools and stack high-water mark monitoring during verification testing are non-negotiable.
Hardware Considerations
IEC 60601-1 — the electrical safety standard for medical devices — imposes isolation and leakage current requirements that directly affect your PCB design around the STM32. If your device makes patient contact, you need to think carefully about creepage and clearance distances, optoisolation on communication interfaces, and how your power supply achieves the required means of protection.
The STM32 itself is not certified to any medical standard — it is a commercial component. Your design controls and risk management process are what make the system safe, not the component datasheet.
Watchdog Timers and Fault Handling
The STM32 includes both an independent watchdog (IWDG) and a window watchdog (WWDG). In a medical device, both should be used and both should be documented in your risk analysis as risk control measures. The independent watchdog runs off its own RC oscillator and will reset the device even if the main clock fails — critical for devices where a hung processor could have patient safety implications.
Beyond watchdogs, your firmware should include explicit fault handlers for HardFault, MemManage, BusFault, and UsageFault. Do not let these handlers spin in an infinite loop — log the fault, capture the stack frame, and perform a controlled reset. In a regulated device, that fault log may become evidence in an investigation.
What to Get Right From the Start
The most expensive mistakes in medical device firmware happen early. Choosing the wrong processor variant before understanding your full peripheral requirements. Starting to write application code before the software architecture is reviewed. Skipping unit tests because the schedule is tight. These decisions compound over time and become very expensive to unwind during verification.
Our recommendation: spend the first weeks of a project on requirements and architecture. Define your software items, their safety classifications, and their interfaces before a line of application code is written. The STM32 will handle whatever you build on top of it — the question is whether your process can support the claim that what you built is safe.
If you are starting a medical device project and evaluating the STM32 family for your platform, we are happy to talk through the technical and regulatory considerations. Reach out to the SiGenix team.