Legal and Illegal PST Transition Checks: Step-by-Step Walkthrough

Step-by-step analysis walkthrough

Use this sequence when owning Legal and Illegal PST Transition Checks in a low-power verification review.

1. Freeze deterministic reproducer with mode and seed metadata.

2. Trace domain, supply, and handshake sequence around first mismatch.

3. Correlate assertion failures with waveform and intent checkpoints.

4. Separate setup/config issues from true design intent violations.

5. Run one hypothesis branch at a time and record disproof evidence.

6. Apply minimal fix and validate on local and suite-level LPV runs.

Artifacts to collect

• Transition-arc checker specification with guard predicates, timeout rules, and illegal-arc diagnostics taxonomy.

• power-state transition log

• cross-domain boundary trace

• assertion failure bucket report

• post-fix regression closure summary

Decision memo template

LPV DECISION MEMO - Legal and Illegal PST Transition Checks
symptom:
phase:
root cause:
fix:
validation:
owners: DV assertion owner, power controller RTL lead, firmware sequencing owner, formal verification owner, SoC integration owner

Low-power verification deep dive

Power-state correctness is a protocol contract: legal transitions, robust sequencing, and safe concurrent event handling.

Concept diagram

PST CONTROL LOOP

state request -> legality check -> handshake sequencing -> mode entry -> monitored exit

Metric graph

STATE RISK MIX

illegal transitions     ██████
sequence race bugs      █████
stable mode paths       ████████

Metrics and artifacts to collect

• PST legality matrix

• illegal transition histogram

• entry/exit handshake coverage

• mode sequencing anomaly log

Mini case study

A sporadic low-power failure closed only after proving a wake-versus-thermal race in PMU transition sequencing.

Debug branches

• Validate legal state graph first.

• Stress concurrent control events and asynchronous wakeups.

• Bind fixes to explicit transition and owner contracts.

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.

Principal LPV review addendum

Legal and Illegal PST Transition Checks should be reviewed as a transition integrity system, not just isolated checks.

Use Illegal transition escape rate, transition-checker latency to first error, and percentage of legal arcs exercised with pass/fail evidence. as alarm and Transition-arc checker specification with guard predicates, timeout rules, and illegal-arc diagnostics taxonomy. as proof.

Power-state verification is a protocol verification problem: legal transitions, ordering contracts, and corner-case concurrency. Closure quality comes from reproducible evidence and explicit owners.