Certified functional safety run-time system (FuSa RTS)

Arm’s FuSa RTS is a set of certified software components for speeding up final safety certification in a wide range of embedded applications. It enables developers use the highest safety integrity levels (SIL) for their end applications. This set of qualified components is highly optimized for Arm Cortex-M processors. It contains a robust real-time operating system (RTOS), an independent processorabstraction layer and a verified C library. FuSa RTS is certified by TÜV SÜD for use in a wide range of safety standard certification processes.

Covered safety standards:

• Automotive: ISO 26262, ASIL D
• Industrial: IEC 61508, SIL 3
• Medical: IEC 62304, Class C
• Railway: EN 50128, SIL 4

FuSa RTS components



Safety variant of Keil RTX5- a proven and well-established RTOS in the embedded space. Its predecessors have been around for more than 20 years. The latest implementation is the reference design for the CMSIS-RTOS API v2. It is easy to use and well supported within the μVision IDE/debugger, which features RTX aware tools enabling you to quickly debug your applications. It offers flexible, low-latency scheduling, allowing you to use the best suited one in your application. It delivers fully deterministic behavior meaning that events and interrupts are handled within a predefined time (deadline). Your application can rely on consistent and known process timings. Finally, it is specifically written for applications running on Arm Cortex-M based MCUs. It runs quickly and requires only minimal MCU resources with a memory footprint as small as 5 KB (ROM

FuSa Event Recorder

Safety-verified Event Recorder offers an API (function calls) for event annotations to be added to
the application code. These functions record events along with timestamps and additional
information. The data is stored in the event buffer located in the RAM of the target hardware, so
that it is available even in Cortex-M0+ devices. The μVision debugger reads the content of the
event buffer and displays it in multiple windows, depending on the data and its usage.


The Arm specific part of CMSIS-Coreprovides a hardware abstraction layer (HAL) for Cortex-M processor registers with standardized definitions for the SysTick, Nested Vectored Interrupt Controller (NVIC), System Control Block (SCB), FPU registers, as well as core access functions

FuSa C library

This library implements a restricted subset of functions specified in the ISO C99 C language standard and comes with usage guidelines and examples on how to work effectively with it

Productivity boosting IDE integration

FuSa RTS components are verified for use with safety-qualified Arm C/C++ compiler and natively supported in Arm Keil MDK development tools. This integration significantly simplifies system design, development, validation and certification processes for safety-critical applications.


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