| Aspect | Guidance | Good Example | Bad Example |
|---|---|---|---|
| Scope | State what must NOT happen (negative requirement) | 'Avoid unintended EPS torque > 3 Nm above driver intent' | 'Ensure EPS works correctly' (not a safety requirement) |
| Quantification | Include measurable limits where possible | 'Emergency braking activation only when deceleration demand > 0.3g AND object confidence > 95%' | 'Only activate emergency braking when appropriate' |
| ASIL | State the ASIL directly on the goal | '[ASIL-D] Avoid unintended....' | Safety goal without ASIL |
| Traceability | Reference the hazardous event | 'Derived from HE-04 (unintended AEB, highway)' | No reference to HARA |
| Safe state | State what the system should do instead | '...; safe state: maintain current speed, alert driver' | No safe state defined |
Safety Goal Formulation
Safe States: Design Considerations
| System | Primary Hazard | Safe State | Transition Time |
|---|---|---|---|
| EPS (electric power steering) | Unintended steering torque | Remove motor torque; driver uses manual steering | < 50 ms (FTTI) |
| AEB (emergency braking) | Inadvertent braking at speed | Disable AEB; maintain cruise; alert driver | < 20 ms (FTTI) |
| Throttle-by-wire | Unintended acceleration | Close throttle; apply engine brake; alert driver | < 100 ms |
| ADAS domain controller | Sensor fusion failure | Disable all ADAS features; driver notification | < 500 ms |
| Gateway ECU | Loss of safety message routing | Default to fail-safe values; log fault | < 10 ms |
Fault Tolerance Time Interval (FTTI)
FTTI, FHTI, and FSM Timing Relationship
t=0: Fault occurs in hardware/software
│
├── Fault detection begins (diagnostic runs)
│
t=FHTI: Fault Handling Time Interval ends
(fault has been detected and reported)
│
├── Safety mechanism activates (transition to safe state)
│
t=FTTI: Fault Tolerance Time Interval ends
(must be in safe state before hazardous event can occur)
Example: AEB inadvertent activation
├── FTTI = 20 ms (time from AEB activation request to potential hazardous event)
├── FHTI = 10 ms (detection must complete in half of FTTI — guideline)
└── FSM must transition to safe state within remaining 10 ms
Calculation of FTTI:
For AEB inadvertent activation: FTTI = reaction_time_following_driver
Conservative: 1.2s average brake reaction time
But: at 130 km/h with 2s gap, deceleration starts immediately
→ FTTI ≈ 200ms (time until deceleration creates unsafe gap closure)
→ Diagnostic must detect in < 100ms; safe state within 200msFunctional Safety Concept (FSC) Structure
Markdownfsc_structure.md
# Functional Safety Concept — FCAB Item
## Safety Goal 1 (SG-01)
**[ASIL-D]** Avoid unintended activation of emergency braking above 5 km/h unless
a collision-imminent object is detected with confidence ≥ 95%.
**Safe state:** Disable emergency braking; maintain driver-commanded deceleration;
activate FCW warning; log fault.
**FTTI:** 200 ms from inadvertent brake request to safe state.
## Functional Safety Requirements (FSRs) derived from SG-01:
| ID | Requirement | ASIL |
|-------|-----------------------------------------------------------------|--------|
| FSR-01| The FCAB system shall only issue emergency brake requests when | ASIL-D |
| | radar AND camera independently confirm object with TTC < 1.5s | |
| FSR-02| The FCAB system shall detect internal sensor fusion failure | ASIL-D |
| | within 100 ms and disable emergency braking | |
| FSR-03| The FCAB system shall monitor radar communication | ASIL-D |
| | and disable AEB if radar timeout > 50 ms | |
| FSR-04| The FCAB system shall transition to safe state within 200 ms | ASIL-D |
| | of detecting a safety-relevant fault | |
## Allocation of FSRs to System Elements
- FSR-01: FCAB Domain Controller (perception fusion software)
- FSR-02: FCAB Domain Controller (self-monitoring software + hardware)
- FSR-03: FCAB Domain Controller (communication watchdog)
- FSR-04: FCAB Domain Controller + Brake System ECU (interface)Summary
Safety goals are the top-level safety requirements from which all downstream requirements are derived — every TSR, SSR, and hardware requirement must be traceable back to a safety goal. The FTTI is the most critical timing parameter: it determines the diagnostic latency budget for all safety mechanisms. If FTTI = 200 ms, and FHTI must be ≤ 100 ms, then every diagnostic cycle time, communication timeout, and software task period must be designed to fit within 100 ms. The functional safety concept bridges the gap between abstract safety goals and concrete system architecture decisions — it is where the first technical safety decisions are made.
🔬 Deep Dive — Core Concepts Expanded
This section builds on the foundational concepts covered above with additional technical depth, edge cases, and configuration nuances that separate competent engineers from experts. When working on production ECU projects, the details covered here are the ones most commonly responsible for integration delays and late-phase defects.
Key principles to reinforce:
- Configuration over coding: In AUTOSAR and automotive middleware environments, correctness is largely determined by ARXML configuration, not application code. A correctly implemented algorithm can produce wrong results due to a single misconfigured parameter.
- Traceability as a first-class concern: Every configuration decision should be traceable to a requirement, safety goal, or architecture decision. Undocumented configuration choices are a common source of regression defects when ECUs are updated.
- Cross-module dependencies: In tightly integrated automotive software stacks, changing one module's configuration often requires corresponding updates in dependent modules. Always perform a dependency impact analysis before submitting configuration changes.
🏭 How This Topic Appears in Production Projects
- Project integration phase: The concepts covered in this lesson are most commonly encountered during ECU integration testing — when multiple software components from different teams are combined for the first time. Issues that were invisible in unit tests frequently surface at this stage.
- Supplier/OEM interface: This is a topic that frequently appears in technical discussions between Tier-1 ECU suppliers and OEM system integrators. Engineers who can speak fluently about these details earn credibility and are often brought into critical design review meetings.
- Automotive tool ecosystem: Vector CANoe/CANalyzer, dSPACE tools, and ETAS INCA are the standard tools used to validate and measure the correct behaviour of the systems described in this lesson. Familiarity with these tools alongside the conceptual knowledge dramatically accelerates debugging in real projects.
⚠️ Common Mistakes and How to Avoid Them
- Assuming default configuration is correct: Automotive software tools ship with default configurations that are designed to compile and link, not to meet project-specific requirements. Every configuration parameter needs to be consciously set. 'It compiled' is not the same as 'it is correctly configured'.
- Skipping documentation of configuration rationale: In a 3-year ECU project with team turnover, undocumented configuration choices become tribal knowledge that disappears when engineers leave. Document why a parameter is set to a specific value, not just what it is set to.
- Testing only the happy path: Automotive ECUs must behave correctly under fault conditions, voltage variations, and communication errors. Always test the error handling paths as rigorously as the nominal operation. Many production escapes originate in untested error branches.
- Version mismatches between teams: In a multi-team project, the BSW team, SWC team, and system integration team may use different versions of the same ARXML file. Version management of all ARXML files in a shared repository is mandatory, not optional.
📊 Industry Note
Engineers who master both the theoretical concepts and the practical toolchain skills covered in this course are among the most sought-after professionals in the automotive software industry. The combination of AUTOSAR standards knowledge, safety engineering understanding, and hands-on configuration experience commands premium salaries at OEMs and Tier-1 suppliers globally.