Legal and Illegal PST Transition Checks: Worked Example

Worked example

Worked Example for Legal and Illegal PST Transition Checks is anchored on Illegal transition escape rate, transition-checker latency to first error, and percentage of legal arcs exercised with pass/fail evidence.. Convert observations into mechanism-backed and owner-bound actions.

A regression appears in Illegal transition escape rate, transition-checker latency to first error, and percentage of legal arcs exercised with pass/fail evidence.. Strong closure isolates first failing boundary, proves mechanism, applies one reversible fix, and validates blast radius before release.

Execution lens

LOW-POWER VERIFICATION FLOW - Legal and Illegal PST Transition Checks

power intent and mode definitions
      |
      v
domain controls and transition sequencing
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      v
simulation behavior (isolation, retention, corruption)
      |
      v
assertions and coverage evidence
      |
      v
triage, bounded fix, and signoff closure

Decision matrix

EVIDENCE MATRIX - Legal and Illegal PST Transition Checks

+-----------------------------+--------------------------------+--------------------------------+---------------------------+
| Evidence                    | Tells you                      | Does not prove                 | Next action               |
+-----------------------------+--------------------------------+--------------------------------+---------------------------+
| transition timeline traces  | first failing LP phase         | complete root-cause ownership  | correlate with intent map |
| UPF-aware assertion logs    | contract violations by phase   | silicon product impact         | map to scenario severity  |
| corruption/X classification | actionable vs noisy failures   | legal transition completeness  | replay key mode corners   |
| save/restore snapshots      | state integrity movement       | isolation correctness          | pair with crossing checks |
| before-after regressions    | mitigation movement quality    | long-tail stability            | run full matrix           |
+-----------------------------+--------------------------------+--------------------------------+---------------------------+

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.

Worked-example reasoning

Start by proving phase and boundary assumptions before tuning checks.

Use one reversible change per hypothesis to preserve causality.