Low Power Verification · All levels
Low Power Assertions & Coverage: Tricky Q&A
Senior interview and review questions for Low Power Assertions & Coverage.
Section Q&A bank
Use these drills after completing all topics in Low Power Assertions & Coverage. Answer with context, mechanism proof, artifact, owner, and release decision.
Isolation cells are present and static checks pass. Why can an assertion suite still fail critically during power-down?
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[INT][LPV][LOW-POWER-ASSERTIONS-AND-COVERAGE]
Q: Isolation cells are present and static checks pass. Why can an assertion suite still fail critically during power-down?
A:
Presence does not prove temporal correctness. Assertions frequently expose late isolation enable, wrong clamp polarity, or de-isolation before source-domain validity during transition windows. Low-power bugs are often sequencing defects, so structural pass status can coexist with dynamic protocol corruption unless UPF-aware temporal properties are explicitly checked.
FOLLOW-UP TRAP: Treating isolation-cell insertion reports as equivalent to dynamic isolation correctness.What distinguishes a strong power coverage model from a dashboard showing high aggregate coverage?
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[INT][LPV][LOW-POWER-ASSERTIONS-AND-COVERAGE]
Q: What distinguishes a strong power coverage model from a dashboard showing high aggregate coverage?
A:
A strong model is intent-traceable and risk-weighted: bins correspond to legal/illegal state arcs, transition timing classes, isolation and retention behaviors, and interface activity under mixed-power operation. High aggregate percentages can hide missing critical crosses, such as specific transition plus retention class combinations that are rare but silicon-critical.
FOLLOW-UP TRAP: Accepting high top-line coverage without validating transition and boundary-risk completeness.Why do low-power checker frameworks remain necessary even with extensive assertion-based verification?
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[INT][LPV][LOW-POWER-ASSERTIONS-AND-COVERAGE]
Q: Why do low-power checker frameworks remain necessary even with extensive assertion-based verification?
A:
Assertions prove local temporal contracts, but checker frameworks add multi-transaction context, protocol causality, and richer diagnostics across domain boundaries. This is essential when root cause occurs during a power sequence while visible failure appears later as data mismatch, timeout, or ordering violation in another domain.
FOLLOW-UP TRAP: Assuming assertion count alone guarantees debuggable and complete low-power verification.Coverage is above target, yet signoff review blocks release. What gap usually causes this?
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[INT][LPV][LOW-POWER-ASSERTIONS-AND-COVERAGE]
Q: Coverage is above target, yet signoff review blocks release. What gap usually causes this?
A:
Closure quality is typically missing, not quantity: unresolved high-risk bins, weak waiver rationale, unstable transition regressions, or poor linkage between uncovered bins and mitigation plans. Signoff expects evidence that remaining gaps are either closed by targeted proof/stimulus or consciously accepted with documented risk ownership.
FOLLOW-UP TRAP: Believing a numeric threshold automatically implies low-power signoff readiness.Q&A drill guide
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SYMPTOM -> LPV FAILURE CLASS -> EVIDENCE -> OWNER ACTION -> VALIDATIONSketch while answering
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COVERAGE CLOSURE LOOP
intent risk -> assertions and checkers -> coverage evidence -> closure gaps -> targeted scenariosCommon traps
Prioritize coverage by product-risk scenarios.
Separate actionable assertion classes from setup noise.
Use closure criteria with explicit waiver governance.
Key takeaways
Tie each LPV claim to a concrete transition boundary and one proving artifact.
Prefer minimal reversible fixes with explicit owner and rollback criteria.
Common pitfalls
Treating power-aware failures as random before boundary classification.
Waiving X-prop failures before proving impact and root cause.
Declaring closure without deterministic replay across key modes.