Safety-critical toggles: Managing features that affect timing and WCET in automotive software

Hook: Why your next feature flag could break a timing budget

Feature flags accelerate releases, enable fast rollback and support OTA updates — but in automotive embedded systems they can also change the worst-case execution time (WCET) of safety-critical control paths. If your team treats toggles like web flags, you risk missing timing regressions that can compromise functional safety and certification. This article shows how to integrate modern timing analysis — notably RocqStat (now part of Vector) — into a toggle lifecycle and CI/CD test gates so you can ship features quickly without blowing real-time budgets.

2026 context: why this matters now

In January 2026 Vector Informatik acquired StatInf’s RocqStat product and team, signaling industry consolidation around unified timing and verification toolchains. Vector has stated plans to integrate RocqStat into VectorCAST, which will make static WCET analysis and functional testing more tightly coupled. For teams building software-defined vehicles in 2026, that convergence matters: regulators, OEMs and Tier‑1s increasingly demand traceable evidence that software changes do not violate timing contracts.

Vector's acquisition highlights a trend: verification and timing analysis are moving from separate toolchains into unified workflows that produce evidence for certification and release.

Why WCET belongs in your feature-flag strategy

Traditional feature flags focus on behavior and configuration. In automotive embedded software, a toggle can alter control flow, add algorithmic complexity, or enable additional I/O — any of which affects WCET. You must treat toggles as potential timing regressions and manage them accordingly.

• Safety impact: Timing violations can cause missed deadlines in powertrain, braking, or ADAS stacks.
• Certification risk: ISO 26262 and product approval processes require evidence that timing constraints are met under all authorized configurations.
• Operational risk: OTA enabling of a feature without timing validation can force emergency rollbacks or recalls.

High-level strategy: integrate timing analysis into the toggle lifecycle

The core idea is simple: treat WCET as a first-class attribute of every toggle. That means extending your toggle lifecycle — from design to removal — to include timing classification, analysis, measurement and gated promotion.

1. Classify toggles by timing risk

Not all toggles require exhaustive WCET analysis. Create a risk matrix based on where the toggle executes and the safety criticality of that path.

• High-risk: Toggles that touch control loops, ISR paths, or arbitration code. Require static WCET and measurement-based confirmation for every release.
• Medium-risk: Toggles in perception or path planning where latency influences behavior. Require targeted timing analysis and prioritized measurement.
• Low-risk: User-visible features or diagnostics. Monitor for performance regressions but do not block release unless budgets are violated.

2. Design rules and safe defaults

Apply design constraints so toggles cannot unknowingly increase WCET beyond budgets:

• Safe default: Flags default to the proven, lower‑latency implementation.
• Fail-safe paths: Provide simple, bounded fallback code paths that maintain timing guarantees.
• Bounded allocations: For run-time flags, avoid unbounded loops, dynamic allocation on critical paths, or large worst-case branches.

3. Timing contracts and budgets

Define explicit timing contracts for each critical task. For example, if a control task must complete in 2 ms, specify that any toggle-dependent variant must have a verified WCET <= 2 ms. Store these budgets in the requirements traceability matrix so they appear in certification artifacts.

Integrating RocqStat and VectorCAST into your CI/CD and test gates

Statically verifying WCET with a tool like RocqStat and complementing it with VectorCAST tests gives you both formal timing estimates and functional correctness evidence. With Vector's acquisition of RocqStat, expect tighter integration that produces unified artifacts for safety cases and audits.

Static vs measurement-based vs hybrid analysis

Use a blended approach:

• Static timing analysis (RocqStat): Produces conservative WCET bounds based on code paths, hardware model and cache pipeline modeling. Mandatory for high-risk toggles.
• Measurement-based testing (VectorCAST instrumentation, on-hardware benches): Confirms execution profiles and catches modeling errors. Useful to reduce over-conservatism and identify rare timing combinations.
• Hybrid: Use static analysis to identify worst-case paths, then exercise those paths with targeted test vectors on hardware to validate and tighten bounds.

CI/CD example: test gates for toggles

Place timing analysis in your pipeline early and as a final check before deployment. A practical pipeline includes:

1. Unit tests and static code analysis (MISRA, clang-tidy)
2. Compile with instrumentation for microbenchmarking (if needed)
3. Run RocqStat static timing analysis for the current toggle matrix
4. Run VectorCAST functional tests; collect timing traces
5. Gate: Compare reported WCET against the task’s timing budget; fail pipeline on violations

Example GitLab CI stage (illustrative):

stages:
  - build
  - timing
  - test

build:
  stage: build
  script:
    - make all

wcet_analysis:
  stage: timing
  script:
    - rocqstat analyze --project build/elf --config timing_model.xml --output wcet_report.json
    - python tools/check_wcet.py wcet_report.json --budgets budgets.yaml
  artifacts:
    paths:
      - wcet_report.json

unit_tests:
  stage: test
  script:
    - vectorcast run --project tests/vcast_project
    - python tools/collect_timing_traces.py --artifacts vcast/trace.log
    - python tools/check_wcet.py vcast/trace.log --budgets budgets.yaml

Notes: replace the commands with your toolchain’s CLI. The key is the test gate that programmatically fails the pipeline when WCET > budget.

Managing combinatorial explosion of toggle states

Analyzing every combination of toggles is often infeasible. Use these practical strategies:

• Risk-based selection: Fully analyze combinations only when multiple high-risk toggles can interact on the same critical path.
• Pairwise or orthogonal arrays: Use combinatorial testing to cover interactions efficiently — similar approaches appear in guides on cost-aware combinatorial testing.
• Feature gating groups: Model related toggles as a single multi-mode switch for timing analysis.
• Change impact analysis: Run static dependency analysis to identify which toggles can affect a given task’s call graph, then restrict WCET runs to relevant sets.

Auditability, access control, and certification evidence

Regulators and OEM certifiers require clear, traceable evidence that timing constraints are respected. Make timing analysis part of your audit trail.

What to record

• Per-toggle WCET reports: Store static analysis outputs and measurement traces indexed by toggle version and commit hash.
• Change approvals: Require RBAC-enforced approvals for toggles that affect timing budgets — and align identity controls with the view that identity is central to zero trust.
• Toolchain evidence: Capture tool versions, models, and configuration files used by RocqStat/VectorCAST — include tool qualification notes where required.
• Traceability: Map toggles back to requirements and hazard logs (e.g., HARA) in your DOORS or ALM system.

Access control and production safety

Implement strict controls over who can change high-risk toggles:

• RBAC: Separate roles for development, QA, safety approval and release engineers.
• Signed configurations: Toggle manifests pushed to vehicles must be cryptographically signed and have sequence numbers to prevent rollback to unsafe combinations.
• Audit logs: Immutable logs of toggle state changes, approvals and analysis artifacts — store in SIEM or secure artifact store for audits.

Tool qualification and certification considerations

Tools used to generate evidence for certification may themselves need qualification. VectorCAST is commonly used in safety workflows; with RocqStat integration, expect an even tighter evidence chain. Work with your safety engineering team to:

• Document tool use cases and limitations.
• Collect qualification evidence (test cases, configuration, operational boundaries).
• Include tool outputs in the safety case and ensure traceability from requirements to WCET reports.

Rollback, mitigation and live safety controls

In addition to pre-release gates, design live rollback and mitigation patterns that protect timing budgets at run-time.

Safe rollback patterns

• Kill switch: A high-priority, authenticated command that immediately disables the feature and reverts to the safe default. Ensure the kill path itself preserves timing budgets.
• Graceful degradation: If feature code detects it’s exceeding soft time budgets (via hardware timers or watchdogs), it should disable non-essential processing rather than blocking the control loop.
• Pre-validated fallback: Keep a minimal, pre-verified implementation of the critical path that can be toggled on with minimal latency.

Runtime telemetry and thresholds

Collect lightweight telemetry to detect emerging timing risks post-deployment:

• Per-task execution histograms (p99, max)
• Toggle-state-correlated traces
• Automatic alerting when margins fall below thresholds — and feed those signals into edge sync and low-latency workflows for responsive mitigations.

Practical code patterns: C example for a timing-safe toggle

The following C-style example shows a toggle guarded by a safe-default code path, a timing check, and a fail-safe fallback. This pattern is suitable for a control loop where meeting a deadline is mandatory.

#include <stdint.h>
#include <stdbool.h>
#include "hw_timer.h"  // platform timer API
#include "toggle_cfg.h" // secure toggle manifest

// Timing budget in microseconds
#define CONTROL_BUDGET_US 2000

bool feature_enabled(void) {
    // Read from signed toggle manifest/cache. Access control required.
    return toggle_cfg_get("USE_ADV_CTRL");
}

void simple_control_step(void) {
    // Proven safe implementation
}

void advanced_control_step(void) {
    // New algorithm; may have larger WCET
}

void control_task(void) {
    uint64_t t0 = hw_timer_read_us();

    if (feature_enabled()) {
        advanced_control_step();
    } else {
        simple_control_step();
    }

    uint64_t elapsed = hw_timer_read_us() - t0;
    if (elapsed > CONTROL_BUDGET_US) {
        // Exceeded soft budget; trigger safe fallback next cycle
        toggle_cfg_request_local_disable("USE_ADV_CTRL");
        // Log event for telemetry
        telemetry_log_timing_violation(elapsed);
    }
}

Key points:

• Toggle reads come from a signed, authenticated manifest — not ad-hoc memory.
• Task measures elapsed time and requests local disable if soft budget exceeded.
• Telemetry allows post‑hoc analysis and supports the safety case.

Operationalizing: checklist and actionable takeaways

1. Classify toggles by timing risk and require RocqStat static analysis for high-risk flags.
2. Define timing contracts for every critical task and store them in your ALM traceability matrix.
3. Instrument and measure: combine RocqStat outputs with VectorCAST traces to validate on-target WCET.
4. Gate CI/CD: fail builds automatically when WCET exceeds budgets for the active toggle set.
5. Harden runtime: safe defaults, kill switches, and pre-validated fallbacks must be implemented for safety-critical toggles.
6. Record evidence: store per-toggle reports, tool configurations, approvals and signed manifests in an immutable artifact store for audits.
7. Limit access: enforce RBAC and multi-person approvals for changes that affect high-risk toggles.
8. Plan removal: include toggle deprecation in your lifecycle and re-run WCET analysis when removing or refactoring toggles.

Looking ahead: trends and predictions for 2026+

Expect the following trends through 2026 and beyond:

• Tighter tool integration: Vector's acquisition of RocqStat is a step toward toolchains that produce unified timing and functional evidence for safety cases.
• Automation of safety gates: CI/CD pipelines will commonly include static WCET checks before merge and deployment.
• Feature-flag governance at scale: OEMs will require centralized feature registries with built-in timing metadata and signed manifests for OTA.
• Runtime safety fabrics: More vehicles will include runtime monitors that correlate toggles and timing telemetry and auto‑rollback unsafe configurations.

Final thoughts and next steps

Feature flags are valuable in automotive development, but they require different discipline than in cloud-native apps. By making WCET part of your flag lifecycle, integrating static analysis (RocqStat) with functional testing (VectorCAST), and enforcing CI/CD test gates and access controls, you can enjoy fast deployments while preserving timing safety and certification evidence.

Ready to apply this in your pipeline? Start by identifying your high-risk toggles today, add timing budgets to requirements, and plug a RocqStat run into your CI timing stage. If you already use VectorCAST, watch for the RocqStat integration to simplify producing unified artifacts for your safety case — and use a build vs buy framework when deciding how to integrate.

Call to action

Audit your active toggles for timing risk this sprint. If you want a practical template to add RocqStat timing gates to your CI and toggle management process, request our CI/CD timing-check template and toggle risk matrix — we’ll share a starter configuration tailored to embedded automotive stacks and certification workflows.

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