Title: SW Critical Path & Dependent Failure Analysis | ISO 26262 Academy URL: https://iso26262.academy/features/concepts/sw-critical-path-analysis Description: Learn how to identify safety-critical software execution paths and prioritize verification effort where it matters most. --- Concept guide · ISO 26262-6 · 7 chapters # SW Critical Path & Dependent Failure Analysis Find the software paths that can violate a safety goal, rate component criticality, expose the couplings that defeat independence, and spend verification effort where it changes the outcome. 7 Chapters 6 Figures and interactive visuals 2 Worked examples Included in [Expert](https://iso26262.academy/pricing#plan-advanced) [Preview free](https://iso26262.academy/register?plan=free&from=%2Fconcepts%2Fsw-critical-path-analysis&utm_source=website&utm_medium=cta&utm_campaign=features_concepts) See the chapters Inside the course 1. 01 **Overview** 2. 02 **Critical Path Analysis** 3. 03 **Dependent Failure Analysis** 4. 04 **Methodology** 5. 05 **Templates & Tools** The short version ## Quick answers What is software critical path analysis in functional safety? Software critical path analysis identifies the paths through which a software fault can lead to a safety goal violation. It traces safety-related inputs through processing to safety-critical outputs using control flow, data flow and call relationships, then classifies components and signals by criticality. The result shows where safety mechanisms, reviews and tests have the most effect. What is dependent failure analysis (DFA) in ISO 26262? DFA checks whether elements that are assumed to fail independently actually do. Redundancy, monitoring and ASIL decomposition all rest on independence, and common cause or cascading failures can quietly void it. ISO 26262-9, Clause 7 covers the analysis of dependent failures: the architecture is examined for initiators and coupling factors, and each one is shown to be absent or controlled by a safety measure. Keep going, free - [Demo exam · no account Test yourself with 7 exam-style questions](https://iso26262.academy/demo-exam) Why this course · ISO 26262, Part 6 ## Why it pays for itself ### Verification effort where it matters Rating components and signals by criticality lets you concentrate reviews, tests and safety mechanisms on the paths that can violate a safety goal, instead of spreading effort evenly across code that cannot. ### Common causes made visible Coupling factor classes systematically expose the shared power, buses, memory, teams and tools that quietly defeat redundancy, before one common cause takes out both channels. ### Templates, not blank pages Templates, tool recommendations and checklists for both analyses mean your first analysis starts from structure instead of an empty spreadsheet. After the course ## What you’ll be able to do ### Trace critical paths Follow safety-related signals from input to output and name the paths that can violate a safety goal. ### Rate component criticality Classify software components and use the rating to prioritize reviews and tests. ### Find couplings early Expose shared resources, inputs and development factors that defeat independence. ### Support decomposition Use DFA as the evidence that decomposed elements are sufficiently independent. ### Place mechanisms deliberately Put safety mechanisms on rated critical paths with a documented rationale. The curriculum · 7 chapters ## Chapter by chapter 1. 01 **Overview** See what critical path analysis and dependent failure analysis each answer, and when in a project to perform them. - Critical path analysis - Dependent failure analysis - When to perform them 2. 02 **Critical Path Analysis** Trace safety-related signals through the software step by step and classify components and signals by criticality. - Step-by-step process - Signal path tracer - Criticality classes 3. 03 **Dependent Failure Analysis** Apply coupling factor classes to find dependent failures and see how memory partitioning and E2E protection contain them. - Coupling factor classes - Common cause versus cascading - MPU and E2E mitigation 4. 04 **Methodology** Understand why DFA is the precondition for ASIL decomposition and follow the methodology for both analyses. - Decomposition independence gate - CPA methodology - Safety goal tracing 5. 05 **Templates & Tools** Start from structured templates, recommended tools and checklists for both analyses. - CPA templates - DFA templates - Analysis checklists 6. 06 **Examples** Apply both analyses to a steer-by-wire system and a brake-by-wire system, including a fault-handling timing budget. - Steer-by-wire CPA - Brake-by-wire DFA - Timing budget 7. 07 **Best Practices** Adopt practices for both analyses, connect them to ISO 26262 expectations and measure analysis quality. - CPA best practices - DFA best practices - Example KPIs Read all 7 chapters with Expert. Start with a free account: the complete Functional Safety Concept guide and 5 practice exams a month, then upgrade when you need this guide. [Expert](https://iso26262.academy/pricing#plan-advanced) [Preview free](https://iso26262.academy/register?plan=free&from=%2Fconcepts%2Fsw-critical-path-analysis&utm_source=website&utm_medium=cta&utm_campaign=features_concepts) [Try the 7-question demo exam](https://iso26262.academy/demo-exam) Figures and interactive visuals ## Not just text: the visual toolkit ### Safety-signal path tracer Follow a signal through the software and classify its criticality. ### Common cause versus cascading How one coupling defeats redundancy in different ways. ### Memory partition with MPU A wild write trapped before it corrupts another component. ### E2E frame protection Protection of messages on a shared bus. ### Steer-by-wire timing budget Fault handling against the fault tolerant time interval. Worked examples ## Steer-by-wire paths and brake-by-wire couplings Two systems show the analyses in practice: critical paths in a steer-by-wire architecture and dependent failure couplings in a brake-by-wire design. - Critical paths for normal operation, failure detection and fallback - Coupling factors in a brake-by-wire design - A steer-by-wire fault-handling timing budget - Mitigations for the couplings found Steer-by-wire critical paths Normal operation: from driver input through the primary controller to the motor Unlock in course Built for ## Who this guide is for - Software architects who must show independence between components of different ASILs - Verification leads deciding where review and test budget actually reduces risk - Safety engineers performing dependent failure analysis on redundant architectures - Developers of fail-operational systems such as brake-by-wire and steer-by-wire ## Frequently Asked Questions Common questions about SW Critical Path & Dependent Failure Analysis Coupling factors are shared properties that can make supposedly independent elements fail together or let one fail because of the other. Typical classes are shared resources such as a power rail or memory, shared input information, systematic coupling from common development, people or tools, components of identical type, communication between elements, and unintended interfaces. The guide works through each class with examples and mitigations such as memory protection and end-to-end protection. Early enough that the findings can still change the architecture. A first pass belongs with the software architectural design, when critical paths and couplings are still cheap to redesign, and the analyses are updated as the design and its changes mature. DFA is also a precondition for ASIL decomposition, because decomposition is only valid if the independence it relies on has been shown. The guide has 7 chapters: an overview, critical path analysis with its step-by-step process and criticality classes, dependent failure analysis with coupling factor classes, the methodology and its link to ASIL decomposition, templates and tools, worked examples on steer-by-wire and brake-by-wire systems, and best practices with example KPIs. It includes 6 figures and interactive visuals. A free account starts you off, and the Pro and Expert plans unlock more of the library. ## Running this analysis on a real project? Have an engineer check it, or help you build it. You get written findings on method, coverage and results. From **$1,490** with a written quote before any charge [See how we can help](https://iso26262.academy/features/consulting?service=analysis#sample) ## Start the course today A free account unlocks one full concept guide, 3 work product templates, 1 guided process, the Markov and RBD simulators, and 5 practice exams per month. The Pro and Expert plans unlock more of the 93-guide library. No credit card required. [Preview free](https://iso26262.academy/register?plan=free&from=%2Fconcepts%2Fsw-critical-path-analysis&utm_source=website&utm_medium=cta&utm_campaign=features_concepts) [View Pricing Plans](https://iso26262.academy/pricing) Continue with ## Where this topic leads next. [Browse all 93 guides](https://iso26262.academy/features/concepts#library) - Software [Agile Development Methods in ISO 26262](https://iso26262.academy/features/concepts/agile-development-iso26262) Learn how to integrate Scrum and SAFe with ISO 26262 without compromising safety evidence or audit readiness. Covers safety backlogs, ASIL-aware definition of done, sprint-level traceability, and automated verification gates. 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