Complete Learning Module

SW Critical Path & DFA

Identifying safety-critical execution paths and performing Dependent Failure Analysis for automotive software

12
In-depth chapters
DFA
Dependent Failure Analysis
CFG
Control Flow Graphs
Risk-based
Verification focus
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What You'll Learn

Build complete competency in sw critical path & dfa through structured, progressive learning.

Construct control flow graphs

Build accurate CFGs for safety-critical software modules and identify all execution paths requiring verification

Perform data flow analysis

Trace safety-critical variable definitions and uses to detect potential corruption and propagation of faults

Execute software DFA

Identify dependent failures in software through shared resource analysis and common cause failure assessment

Prioritize verification

Apply risk-based prioritization to allocate review and testing resources to the highest-impact execution paths

Place safety mechanisms

Determine optimal placement of software safety mechanisms to maximize fault detection on critical paths

Achieve structural coverage

Design targeted tests that satisfy MC/DC and branch coverage requirements for ASIL C/D software modules

12 Comprehensive Chapters

Each chapter builds your sw critical path & dfa expertise systematically from foundations to advanced application.

1

Overview

Introduce the concepts of software critical path analysis and Dependent Failure Analysis (DFA) within the ISO 26262 software development framework.

Critical path conceptDFA purposeISO 26262-6 contextAnalysis objectives
2

Critical Path Analysis Methodology

Learn the systematic methodology for identifying, tracing, and documenting safety-critical execution paths in automotive software.

Path identification criteriaTracing methodologyDocumentation formatCoverage metrics
3

Control Flow Analysis

Apply control flow graph (CFG) construction and analysis to identify all execution paths through safety-critical software modules.

CFG constructionBranch analysisLoop boundingUnreachable code detection
4

Data Flow Analysis

Use data flow analysis techniques to track how safety-critical variables are defined, used, and may be corrupted along execution paths.

Def-use chainsVariable lifetimeAliasing detectionCorruption propagation
5

Call Graph Analysis

Construct and analyze software call graphs to identify all functions on the critical path and ensure complete verification coverage.

Static call graphDynamic dispatchRecursive callsDead code identification
6

Safety-Critical Execution Paths

Classify execution paths by safety criticality level and establish criteria for determining which paths require the highest verification rigor.

Criticality criteriaPath classificationASIL taggingPath documentation
7

Risk-Based Verification Prioritization

Apply risk-based prioritization to focus verification resources on the execution paths with the highest potential safety impact.

Risk scoring modelPriority matrixResource allocationCoverage targets
8

Focused Code Reviews

Execute targeted code reviews on safety-critical paths using structured checklists and independence requirements appropriate to ASIL level.

Review scope definitionChecklist customizationIndependence requirementsFinding classification
9

Targeted Testing Strategies

Design test cases specifically targeting critical execution paths to achieve structural coverage requirements mandated by ISO 26262-6.

Path-based test designMC/DC for critical pathsBoundary value analysisEquivalence classes
10

Safety Mechanism Placement

Determine optimal placement of software safety mechanisms along critical execution paths to detect and handle faults before safety goal violations.

Mechanism placement rulesDetection latencyReaction time budgetsCoverage analysis
11

Dependent Failure Analysis

Perform DFA for software to identify shared resources, common cause failures, and cascading failure paths that could violate independence requirements.

DFA scope for SWShared memory analysisCommon cause identificationIndependence violations
12

Best Practices

Consolidate best practices for integrating critical path analysis and DFA into the software development workflow for efficient ISO 26262 compliance.

Tool integrationAutomation opportunitiesReview efficiencyAssessment preparation
ISO 26262-6

6 Critical Path Analysis Diagrams

Experiment with visual tools that bring sw critical path & dfa concepts to life.

Control Flow Graph Example

Annotated control flow graph for a safety-critical SW module showing all execution paths, decision nodes, and critical path highlighting

Call Graph with ASIL Tagging

Software call graph with ASIL level tagging per function showing which functions reside on safety-critical paths requiring highest verification

Data Flow Critical Variable Trace

Data flow diagram tracing safety-critical sensor value from input through processing to actuator output with potential corruption points marked

DFA Shared Resource Map

Diagram identifying shared memory regions, hardware peripherals, and OS resources accessed by multiple ASIL-partitioned software components

Safety Mechanism Placement

Execution path diagram showing optimal placement of runtime checks, watchdogs, and CRC verifications along the critical software path

Verification Coverage Matrix

Matrix mapping critical execution paths to review activities, unit tests, integration tests, and structural coverage achievements

ADAS Software Case

Critical Path Analysis for an ASIL D Lane Keeping Controller

An ADAS software team applied critical path analysis to a lane-keeping assist controller with 85,000 lines of ASIL D code. The analysis reduced the module verification scope by 60% while increasing defect detection density by 3x on the critical paths.

  • Identified 23 unique safety-critical execution paths out of 4,700 total program paths
  • DFA revealed 3 unintended shared memory regions between ASIL D and QM partitions
  • Focused reviews on critical paths found 18 defects vs. 2 found in remaining code
  • MC/DC coverage achieved 100% on critical paths with 40% fewer test cases than full-module approach

Critical Path Checklist

CP-01: All safety-critical inputs are range-checked before first use on the path
29 additional critical path checklist items (unlock Advanced plan)

Master SW Critical Path Analysis

Focus your verification effort where it matters most by identifying and rigorously verifying safety-critical software execution paths

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12 chapters6 technical diagramsRisk-based verification