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.
- Chapters
- 12
- Chapters
- Interactive Tools
- 6
- Interactive Tools
- Case Study
- 1
- Case Study
- Video
- 1
- Video
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.
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.
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.
Chapter by chapter
- 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
- 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
- 03
Temporal Partitioning
Design time-based partitioning strategies using OS scheduling, time windows, and deadline monitoring.
- OS scheduling
- Time windows
- Deadline monitoring
- 04
Spatial Partitioning
Implement memory protection to prevent spatial interference between software components of different ASILs.
- MPU configuration
- Address space isolation
- Stack protection
- 05
Communication Partitioning
Partition inter-process and inter-core communication to prevent data corruption across ASIL boundaries.
- IPC protection
- Shared memory guards
- API restrictions
- 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
- 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
- 08
AUTOSAR Integration
Configure AUTOSAR OS, MemMap, and MemProtection modules to implement FFI partitioning in production software.
- OS configuration
- MemMap setup
- Protection hooks
- 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
Verification & Evidence
Generate verification evidence for FFI partitioning: test strategies, fault injection, and documentation requirements.
- Test strategies
- Fault injection
- Evidence templates
- 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
Best Practices
Apply proven best practices for FFI architecture design, configuration management, and cross-project reuse.
- Architecture guidelines
- Config management
- Reuse strategies
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.
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
Unlock in course
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
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.