Title: Freedom from Interference (FFI) | ISO 26262 Academy URL: https://iso26262.academy/features/concepts/freedom-from-interference Description: Learn how to ensure elements of different ASILs do not interfere through temporal, spatial, and data partitioning. --- Concept guide · ISO 26262-9 §6 / -6 Annex D · 12 chapters # Freedom from Interference Design and verify Freedom from Interference partitioning for mixed-ASIL systems, multi-core processors, and AUTOSAR platforms per ISO 26262-6 and -9. 12 Chapters 6 Interactive Tools 1 Case Study 1 Video Included in Expert [Start learning](https://iso26262.academy/register?plan=free&from=%2Fconcepts%2Ffreedom-from-interference&utm_source=website&utm_medium=cta&utm_campaign=features_concepts) See the chapters Inside the course 1. 01 **FFI Overview** 2. 02 **ISO 26262 FFI Requirements** 3. 03 **Temporal Partitioning** 4. 04 **Spatial Partitioning** 5. 05 **Communication Partitioning** The short version ## Quick answers What is freedom from interference in ISO 26262? Freedom from interference (FFI) is the absence of cascading failures between software elements that could lead to the violation of a safety requirement - in practice, assurance that a lower-ASIL or QM element cannot corrupt a higher-ASIL element sharing the same resources. ISO 26262-6 Annex D structures the interference into three channels: memory (wild writes, stack overflows), timing and execution (blocking, starvation, deadline misses), and exchange of information (corrupted, lost, or delayed data). Together with the coexistence criteria of ISO 26262-9, Clause 6, FFI is what allows mixed-ASIL software to share one processor without every component being developed at the highest ASIL present. When is freedom from interference required? Whenever software elements of different ASILs - or ASIL and QM elements - coexist on shared resources such as a processor, memory, or communication path. ISO 26262-9 allows the lower-rated elements to keep their lower ASIL only if interference with the higher-rated elements is prevented or can be shown not to violate a safety requirement. Without that demonstration, the default position is that all coexisting software must be treated at the highest ASIL, which is usually prohibitively expensive for QM code like diagnostics and comfort functions. Keep going, free - [Article · 7 min read Software in ISO 26262: A Fault With No Failure Rate](https://iso26262.academy/blog/software-in-iso-26262-a-fault-with-no-failure-rate) - [Demo exam · no account Test yourself with 7 exam-style questions](https://iso26262.academy/demo-exam) Why this course · ISO 26262, Part 9, Clause 6 ## Why it pays for itself ### Mix ASILs without lifting everything up Demonstrated freedom from interference is what lets QM and ASIL software coexist on one processor - without it, every component on the ECU inherits the highest ASIL present. ### Configure real partitioning mechanisms Work with MPU regions, OS scheduling windows, deadline monitoring, and AUTOSAR OS-Applications - down to cache partitioning and cross-core interrupt handling on multi-core processors. ### Generate verification evidence Plan the WCET analysis, static analysis, fault injection, and documentation that turn a partitioning design into FFI evidence an assessor will accept, with a checklist to find the gaps. After the course ## What you’ll be able to do ### Design FFI Partitioning Architecture Architect temporal and spatial partitioning strategies that prevent interference between mixed-ASIL software components. ### Configure Memory Protection Specify and verify MPU configurations that enforce spatial isolation between software components of different ASILs. ### Address Multi-Core FFI Challenges Identify and mitigate cache sharing, bus contention, and cross-core interrupt interference in multi-core processor designs. ### Implement FFI in AUTOSAR Configure AUTOSAR OS partitions, MemMap, and MemProtection to implement production-grade FFI in automotive software. ### Generate FFI Verification Evidence Plan and execute FFI verification including WCET analysis, fault injection, static analysis, and documentation. ### Comply with ISO 26262 Parts 6 and 9 Satisfy all normative FFI requirements from ISO 26262 Parts 6 and 9 with justified partitioning decisions and evidence. The curriculum · 12 chapters ## Chapter by chapter 1. 01 **FFI Overview** Understand Freedom from Interference: what it means, why it is required, and where it applies in ISO 26262. - FFI definition - Interference types - Regulatory basis 2. 02 **ISO 26262 FFI Requirements** Map the specific FFI requirements from ISO 26262 Part 6 (software) and Part 9 (mixed ASIL) with clause references. - Part 6 clauses - Part 9 clauses - ASIL mixing rules 3. 03 **Temporal Partitioning** Design time-based partitioning strategies using OS scheduling, time windows, and deadline monitoring. - OS scheduling - Time windows - Deadline monitoring 4. 04 **Spatial Partitioning** Implement memory protection to prevent spatial interference between software components of different ASILs. - MPU configuration - Address space isolation - Stack protection 5. 05 **Communication Partitioning** Partition inter-process and inter-core communication to prevent data corruption across ASIL boundaries. - IPC protection - Shared memory guards - API restrictions 6. 06 **Data Partitioning** Protect safety-relevant data from corruption by lower-ASIL components using data integrity and access control. - Data ownership - Access rights - Integrity verification 7. 07 **Multi-Core Considerations** Address FFI challenges specific to multi-core processors: cache sharing, bus contention, and cross-core interrupts. - Cache partitioning - Bus bandwidth - Cross-core IRQ 8. 08 **AUTOSAR Integration** Configure AUTOSAR OS, MemMap, and MemProtection modules to implement FFI partitioning in production software. - OS configuration - MemMap setup - Protection hooks 9. 09 **Analysis Techniques** Apply formal and semi-formal analysis methods to demonstrate FFI: worst-case execution time, code review, static analysis. - WCET analysis - Static analysis tools - Review criteria 10. 10 **Verification & Evidence** Generate verification evidence for FFI partitioning: test strategies, fault injection, and documentation requirements. - Test strategies - Fault injection - Evidence templates 11. 11 **Common Challenges** Recognize and resolve frequent FFI implementation challenges including false positives, performance impacts, and tool limitations. - False MPU violations - Runtime overhead - Debugging partitioned SW 12. 12 **Best Practices** Apply proven best practices for FFI architecture design, configuration management, and cross-project reuse. - Architecture guidelines - Config management - Reuse strategies Interactive Tools ## Not just text: the visual toolkit ### FFI Partitioning Visualizer Visualize temporal and spatial partitioning boundaries between ASIL components in an interactive system view. ### MPU Configuration Tool Configure memory protection unit regions for your MCU architecture and validate ASIL boundary isolation. ### Multi-Core Interference Analyzer Identify shared resource contention points between cores and model their impact on timing and interference. ### AUTOSAR OS Configurator Explore AUTOSAR OS partition and application configuration options for FFI compliance interactively. ### Temporal Budget Calculator Calculate and validate time partition budgets for mixed-ASIL tasks with deadline monitoring configuration. ### FFI Evidence Checklist Work through the required verification evidence for FFI partitioning with status tracking and gap identification. Real-World Application ## FFI Partitioning for a Mixed-ASIL Body Control Module on a Dual-Core MCU Design and verify Freedom from Interference for a Body Control Module hosting ASIL-B airbag functions alongside QM body comfort functions on a shared dual-core processor. - Temporal partitioning: ASIL-B tasks in 1 ms protected window, QM tasks in 5 ms window with 10% budget margin - MPU configured with 8 regions isolating ASIL-B RAM, stack, and peripheral access from QM software - Multi-core: cache locking applied to ASIL-B code sections; L2 cache monitoring added for shared data regions - AUTOSAR OS: separate OS-Applications with trusted/non-trusted split; MemProtectionHook configured - Verification: 500-cycle fault injection test, 0 FFI violations detected across 1M test iterations FFI Partition Map Core 0 / ASIL-B App: RAM Region 0x2000_0000-0x2000_FFFF [R/W, MPU protected, no QM access] Unlock in course Built for ## Who this guide is for - Architects hosting mixed-ASIL and QM software on a shared ECU - Embedded developers configuring MPU regions or AUTOSAR OS partitions - Multi-core platform engineers dealing with cache sharing and bus contention - Safety engineers assembling the coexistence argument for ISO 26262 Part 9 ## Frequently Asked Questions Common questions about Freedom from Interference Spatial partitioning uses the memory protection unit: MPU regions isolate each partition's RAM, stack, and peripheral access so a wild pointer in QM code traps before the byte changes. Temporal partitioning uses OS-level mechanisms: scheduling windows, execution time budgets, and deadline monitoring bound how much CPU time a lower-ASIL task can steal. Communication and data partitioning complete the picture with protected IPC, shared-memory guards, data ownership rules, and integrity verification across ASIL boundaries. On multi-core parts you additionally manage cache sharing, bus bandwidth, and cross-core interrupts. AUTOSAR Classic maps partitions onto OS-Applications with a trusted/non-trusted split: the OS configures the MPU per partition, MemMap places code and data into protected sections, and protection hooks define the reaction when a violation is trapped - from terminating the offending task to a partition restart. The course walks the OS configuration, MemMap setup, and MemProtection modules, and its case study configures exactly this for a body control module hosting ASIL B and QM functions on a dual-core MCU. Twelve chapters run from the ISO 26262 Part 6 and Part 9 requirements through temporal, spatial, communication, and data partitioning to multi-core and AUTOSAR specifics, analysis techniques, and verification evidence. Six interactive tools support the material, and the case study partitions a mixed-ASIL body control module on a dual-core MCU. A free account starts you off, and the Pro and Expert plans unlock more of the library. ## Start the course today A free account unlocks one full concept guide, 3 work product templates, 1 guided process, the Markov simulator, and 5 practice exams per month. The Pro and Expert plans unlock more of the 78-guide library. No credit card required. [Start learning](https://iso26262.academy/register?plan=free&from=%2Fconcepts%2Ffreedom-from-interference&utm_source=website&utm_medium=cta&utm_campaign=features_concepts) [View Pricing Plans](https://iso26262.academy/pricing)