Arm FuSa RTS

Arm FuSa RTS (Runtime System) is the safety-qualified runtime bundle that pairs with Arm Compiler for Embedded FuSa for Cortex-M-based safety-critical firmware. Per Arm’s FuSa RTS deck, the bundle includes FuSa RTX RTOS, FuSa CMSIS-Core, supporting CMSIS components, and an Event Recorder, the run-time pieces a Cortex-M safety project needs to land its application code on a TUV SUD-qualified foundation. FuSa RTS is distinct from the Arm Certified C Library, which is a separate ~200-function C library subset with its own Qualification Kit and distribution licence, see the note below.

The FuSa RTS is qualified to the same safety standards as the FuSa Compiler, per Arm’s published AC6 FuSa product page: ISO 26262 (Automotive) ASIL D, IEC 61508 (Industrial) SIL 3, EN 50716 (Railways) SIL 4, and IEC 62304 (Medical) Class C. FuSa RTS supports Cortex-M cores only (8 cores publicly documented: M0, M0+, M3, M4, M7, M23, M33, M55). Cortex-R and Cortex-A safety designs use different qualified run-time strategies, see the “Cortex-M Core Support Matrix” and the Cortex-R / Cortex-A note further down.

FuSa RTS vs Arm Certified C Library: what’s bundled where

Two related Arm safety deliverables that are often conflated:

• Arm FuSa RTS (this product), the runtime bundle: FuSa RTX RTOS + FuSa CMSIS-Core + Event Recorder + supporting CMSIS components. Cortex-M only. Bundled in MDK Professional.
• Arm Certified C Library: a separate ~200-function C library subset (subset of standard C runtime functions) with its own Qualification Kit and its own licence. Available with AC6.22 LTS / Arm Development Studio Gold FuSa.

This page describes Arm FuSa RTS; if you need the C library subset specifically, ask about the Arm Certified C Library product.

What FuSa RTS Covers

Component	Description
FuSa RTX RTOS	Qualified preemptive RTOS kernel, threads, mutexes, semaphores, timers. Same CMSIS-RTOS2 API as standard RTX5 with safety-class extensions and MPU-based spatial isolation support
FuSa CMSIS-Core	Qualified Cortex-M startup code, exception handlers, and core-peripheral abstraction, the boundary between application code and silicon is itself qualified
FuSa Event Recorder	Qualified runtime telemetry capture for fault-injection testing, post-deployment safety analysis, and ASIL-D evidence trails
Software Test Library (STL)	Qualified self-test library covering Cortex-M core integrity checks at runtime
Supporting CMSIS components	Qualified driver abstractions and supporting libraries surrounding the run-time
Qualification Evidence	TUV SUD certificate, Safety Manual, Test Report, Defect Report, and Development Process Report, the same 5-document Qualification Kit shipped with AC6 FuSa

Note: a qualified C library is not part of FuSa RTS. That deliverable is the separate Arm Certified C Library product, see the “FuSa RTS vs Arm Certified C Library” section above.

FuSa RTS in the Safety Toolchain

The FuSa RTS works exclusively with the Arm Compiler for Embedded FuSa, together they form a fully qualified compilation and runtime toolchain. This combination is available standalone, as part of Keil MDK Professional, or as part of Arm Development Studio Gold FuSa edition. For safety certification, both the compiler and the runtime library must be qualified; using a certified compiler with an unqualified C library would leave a gap in the tool qualification chain that assessors would flag. GSAS provides FuSa RTS licensing alongside the FuSa Compiler and assists Indian engineering teams with tool qualification documentation and safety assessor preparation.

Standards Coverage

The FuSa RTS qualification covers the same standards envelope as the FuSa Compiler:

Standard	Level	Domain
ISO 26262	ASIL D	Automotive
IEC 61508	SIL 3	Industrial
EN 50716	SIL 4	Railway (supersedes EN 50128)
IEC 62304	Class C	Medical devices

The same TÜV SÜD-issued qualification evidence package, Safety Manual, Defect Report, Test Report, Development Process Report, covers all four standards. Indian teams certifying to multiple standards simultaneously (a Tier-1 ECU programme on ISO 26262 ASIL-D plus IEC 61508 SIL-3 industrial-grade variants of the same firmware, for example) qualify both standards from one tool-qualification effort.

Cortex-M Core Support Matrix

FuSa RTS supports eight Cortex-M cores publicly:

Core	Notes
Cortex-M0	Smallest footprint; widely used in low-power industrial sensors
Cortex-M0+	Indian medical-device and IoT-edge use, with SysTick/MPU
Cortex-M3	Established generation; long-running automotive and motor-control programmes
Cortex-M4	DSP extensions; audio, motor-control, sensor-fusion
Cortex-M7	High-performance Cortex-M; cache + double-precision FP
Cortex-M23	Armv8-M baseline; TrustZone-M for security-aware safety designs
Cortex-M33	Armv8-M mainline; Indian Tier-1 next-generation ECUs
Cortex-M55	Armv8.1-M with Helium MVE; edge-AI safety designs

Cortex-R and Cortex-A use different qualified run-time strategies (Cortex-R safety designs typically standardize on AC6 FuSa directly with the application providing the run-time; Cortex-A safety designs typically standardize on AUTOSAR-Adaptive on top of POSIX).

Application Notes Indian Teams Reference Most

Arm publishes safety-class application notes on developer.arm.com covering FuSa RTS deployment with Keil MDK Professional (project setup, qualified-RTOS integration, safety-evidence trail) and safety-class API patterns including MPU-based spatial isolation and thread-watchdog idioms for Cortex-M designs. The deeper application notes are available to Arm customers via developer.arm.com sign-in. GSAS walks Indian customers through the relevant guidance during the FuSa RTS adoption engagement.

Migration from AC6.16 LTS to AC6.22 LTS

The FuSa RTS qualification ships paired with the matching FuSa Compiler generation. Indian Tier-1 / Tier-2 automotive, railway, and industrial customers running AC6.16 LTS today will move to the matching FuSa RTS generation as part of the AC6.22 LTS migration and re-run the safety re-verification cycle. See Planning the AC6.16 LTS → AC6.22 LTS Migration for Indian FuSa Programs for the 4-phase 16-28-week safety re-verification plan.

Why Indian Safety-Critical Teams Buy FuSa RTS from GSAS

• INR procurement: GeM, SAP Ariba, Coupa, TReDS supported. GST-compliant invoicing.
• Tool-qualification documentation support: we walk your safety case through the FuSa RTS qualification artefacts, help your team build the tool-qualification evidence chain, and brief your TÜV auditor / notified-body assessor.
• MPU spatial-isolation guidance: practical patterns for Cortex-M MPU-based safety partitioning, drawing on Arm’s published safety-class application notes.
• Local engineering: reachable from Bengaluru, Hyderabad, Chennai, Pune, Mumbai, Delhi NCR, and Visakhapatnam.
• Authorized Arm engineering partner since 2018: a long-standing Arm tools partner across India.

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