Low Power Verification · All levels

X-Propagation in LPV: Debug Playbook

Debug Playbook for X-Propagation in LPV.

Debug playbook

Debug Playbook for X-Propagation in LPV is anchored on illegal transition rate, corruption incidence, and deterministic replay quality under low-power scenarios. Convert observations into mechanism-backed and owner-bound actions.

Freeze seed, metadata, and boundary under investigation.
Locate first persistent low-power phase divergence.
Classify mechanism: setup, transition, boundary, retention, or X-prop class.
Apply one focused reproducer and one bounded fix.
Re-run determinism and broader regression matrix.

Review memo template

diagram

LPV REVIEW MEMO - LPV Debug & Signoff / X-Propagation in LPV

1. Symptom
   - Failing metric: illegal transition rate, corruption incidence, and deterministic replay quality under low-power scenarios
   - Trigger context: <seed/mode/sequence>
   - First failing phase: <entry/off/exit/boundary>

2. Mechanism hypothesis
   - Candidate mechanism: X-propagation in low-power verification is not just unknown logic from uninitialized flops; it is often intentional corruption caused by domain shutdown and therefore carries power-state meaning. Debug requires separating expected corruption from dangerous leakage by correlating X onset with power intent events: isolation assertion timing, switch acknowledgment, retention save/restore windows, and legal PST transitions. Teams should instrument checks that tag each X with boundary origin, power state, and control sequence so failures are triaged as missing isolation, wrong clamp policy, illegal access to an off domain, or simulator setup gap. Unique LPV risk appears when optimistic X handling masks protocol violations in active domains, so signoff-grade environments use pessimism-aware runs and targeted assertions to prove X cannot silently bypass safety-critical handshakes.
   - Competing hypotheses: setup, transition race, boundary bug, retention drift, X-prop noise
   - Missing evidence: <trace/assertion/report>

3. Proposed action
   - Smallest reversible change: <intent/RTL/checker/flow>
   - Expected movement: <failure trend/replay stability>
   - Regression risk: compatibility, coverage, signoff delay

4. Signoff
   - Required artifact: evidence packet for X-Propagation in LPV: transition timeline, assertions, and before-after replay summary
   - Required owners: LPV lead, power-intent owner, LPV Debug & Signoff owner
   - Final decision: ship, bounded rollout, rollback, or escalate

Low-power verification deep dive

Signoff confidence comes from triage discipline, reproducible proof, and explicit residual-risk decisions.

Concept diagram

diagram

LPV SIGNOFF LADDER

reproduce -> classify -> isolate boundary -> bounded fix -> replay -> signoff decision

Metric graph

diagram

SIGNOFF CONFIDENCE

open ambiguous failures  ██████
reproducible closures    ███████
residual-risk unknowns   ███

Metrics and artifacts to collect

X-prop triage classification report
bug root-cause closure packet
regression stability and recurrence trend
signoff checklist completion matrix

Mini case study

A signoff block cleared after the team replaced broad waivers with boundary-specific evidence and replay criteria.

Debug branches

Classify X behavior before broad waiving.
Capture one definitive artifact packet per closure claim.
Define residual risk and rollback path at signoff.

Senior review question

Ask: what exact low-power transition boundary failed first, and which artifact proves the closure claim reproducibly?

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.

Debug ladder

Sequence: reproduce -> classify -> isolate boundary -> prove mechanism -> bounded fix.

Avoid mixed fixes before first-principles classification.

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