By Markus Stix and Stefan Pruisken

For decades, the world of automotive software has been dominated by AUTOSAR Classic – a reliable but heavyweight standard. Recently, however, OEMs and suppliers are increasingly investigating lightweight alternatives like FreeRTOS. Even though FreeRTOS is not an equivalent replacement for AUTOSAR Classic, it brings significant value to the developers of embedded devices.

FreeRTOS serves as a lightweight, open real-time operating system (RTOS) that is particularly well-suited for applications demanding little resources. The FreeRTOS kernel and other FreeRTOS libraries are distributed for free under the MIT open-source license1. It is available for all major architectures (Arm, RISC-V, MIPS, Intel) and allows high flexibility in sourcing the right MCU and semiconductor vendor. For example, Infineon also provides FreeRTOS support as part of their MCU Starter Kits2.

What OEMs can gain from using FreeRTOS

Value	Description
Lightweight footprint	Minimal RAM/ROM usage, ideal for cost-sensitive platforms
Open licensing	No license fees, no vendor lock-in
Portability	Runs on many architectures (e.g., ARM Cortex-M, RISC-V)
Agility & transparency	Immediate access to code, fast customization; great for early-stage projects
DevOps-friendly	Easily integrates with CI/CD pipelines and modern development workflows

FreeRTOS does not provide an automotive-grade middleware stack and associated tooling out of the box. Essential middleware functions like communication, diagnostic, or system state management are missing and force the OEM developers to find individual solutions. Thus, it is not a surprise that today’s OEMs experiment with hybrid solutions based on FreeRTOS & AUTOSAR Classic modules.

FreeRTOS Challenge	Description
No Standardized Software: Architecture and the need to build a solution on heterogeneous software layers	Each OEM/Tier-1 must define its own software components and architecture layers, which might introduce unexpected incompatibility and misbehavior. This creates risks when scaling across multiple projects that interface with different industry partners.
Maintenance & Long-Term Support	FreeRTOS-based projects need strong internal governance.

While AUTOSAR with SAFERTOS3 is still the dominant solution for safety-critical ECUs, Synopsys is seeing solutions that use FreeRTOS in safety critical systems. Additionally, we are seeing market transformations for:

• Microservice-based architecture
• Zone controllers
• Software-defined vehicles

These concepts demand modular, scalable software – and for many domains, AUTOSAR Classic is too rigid and resource-heavy. FreeRTOS is filling the gap and is gaining share.

Importance of Virtual ECUs in the development and validation of ECUs

Virtual ECUs (vECUs) have significantly changed software development and testing within the automotive industry. By simulating the functionality of physical ECUs in a virtual environment, vECUs facilitate quicker software development and validation, and significantly reduce the need for physical hardware. This allows software teams to initiate development and testing even in the beginning when no actual hardware is available. More importantly, enabling Software-Defined Vehicle (SDV) processes, such as Continuous Integration and Continuous Deployment (CI/CD), utilizes vECUs throughout the entire software lifecycle and enables the fastest feedback on code changes and bug fixes.

Validating FreeRTOS-based ECUs in SIL simulations

It is crucial for leading Software-in-the-Loop (SIL) tools like Synopsys Silver to address the latest industry requirements by supporting the virtualization of open-source operating systems such as FreeRTOS. This enables customers to use Silver in known comprehensive workflows to build vECUs. It was never simpler to generate FreeRTOS-based vECUs for deterministic and reproducible SIL test execution.

Silver has prioritized delivering a simulation solution that is independent of any software stack or framework. Today, this enables our customers to benefit from the same maturity level of simulation capabilities and expertise to explore and adapt new approaches like FreeRTOS/SAFERTOS for automotive software development. Silver provides a comprehensive, automotive-grade development environment – also applicable for RTOS-based ECUs – featuring:

• vECU creation and integration into a vast co-simulation and 3rd party tool ecosystem to enable closed-loop, multi-node validation and verification based on automotive standards

• Reproducible simulation results by deterministic task scheduling decoupled from the host system’s time

• Single- and multi-core support for realistic simulation behavior

• Intuitive hands-on stimulation, measurement and debugging during simulation runtime

• Interactive UI and headless simulation execution

• Windows and Linux support

The listed features by far exceed the capabilities of other RTOS simulators, which lack the requirements of automotive software development and testing teams and their supply chain.

The solution lends itself to shift left not only start of production (SOP) dates, but also technological assessments and decision making as described above. For instance, porting resource intensive AUTOSAR Classic software components to a lightweight RTOS-based stack running on a separate core.

This video showcases how to debug a Silver vECU that runs an Onboard Charging software component on top of FreeRTOS, in addition to a MICROSAR-based Battery Management System distributed on two cores.

Conclusion

Automotive OEMs and suppliers are looking at FreeRTOS as a lightweight, open RTOS. Automotive ECUs can be built utilizing a hybrid of FreeRTOS and AUTOSAR to enable modular, scalable software.

With the advanced feature set outlined in this blog, the Silver vECU solution is a transformative tool for automotive software development and validation. Its integration capability, deterministic simulation, multi-core realism, and flexible runtime options empower engineering teams to accelerate production timelines and make informed technological decisions early in the process. By supporting industry standards and offering compatibility across platforms, it surpasses conventional RTOS simulators and stands as an essential asset for modern automotive software projects.

References

1. https://www.freertos.org/Documentation/02-Kernel/01-About-the-FreeRTOS-kernel/04-Licensing
2. AURIX TC3x from Infineon supports FreeRTOS: https://www.infineon.com/market-news/2024/infatv202411-027
3. SAFERTOS is a pre-certified safety Real Time Operating System (RTOS) for embedded processors: SAFERTOS, the safety certified RTOS – available pre-certified to IEC 61508

Stefan Pruisken is a senior director of product management in the Systems Software line of business within PMG and manages the Synopsys Silver product.

Markus Stix

(all posts) Markus Stix is a senior staff technical product manager responsible for definition, realization, and deployment of Synopsys’ Silver product. He holds a BSc in Technical Computer Science and an MSc in Information Systems from the University of Applied Sciences Ulm.