Low Power Verification · All levels

Save/Restore Handshake Sequencing: Debug Playbook

Debug Playbook for Save/Restore Handshake Sequencing.

Debug playbook

Debug Playbook for Save/Restore Handshake Sequencing is anchored on Handshake protocol compliance rate, save-to-off and restore-to-functional timing margin, and timeout escape count.. 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 - Retention & Restore / Save/Restore Handshake Sequencing

1. Symptom
   - Failing metric: Handshake protocol compliance rate, save-to-off and restore-to-functional timing margin, and timeout escape count.
   - Trigger context: <seed/mode/sequence>
   - First failing phase: <entry/off/exit/boundary>

2. Mechanism hypothesis
   - Candidate mechanism: Save/restore sequencing must be verified as a protocol, not only as a waveform snapshot. The environment should assert legal ordering between save request, save acknowledge, isolation enable, clock gating, power switch transitions, and restore deassertion. Verification should model realistic controller jitter, firmware delays, and concurrent requests from neighboring domains so sequencing robustness is validated under system pressure. Critical checks include ensuring restore is blocked until clocks and supplies are stable, retained state is visible before dependent logic resumes, and no stale handshake from a prior cycle leaks into the next power event. Negative tests should intentionally inject early wake, missing save ack, and double-trigger conditions to prove recovery paths and watchdog behavior instead of assuming clean operation.
   - 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: Temporal handshake checker suite with protocol assertions, timeout diagnostics, and scenario-wise latency histograms.
   - Required owners: power controller owner, firmware/power management owner, low-power verification owner, SoC integration owner
   - Final decision: ship, bounded rollout, rollback, or escalate

Low-power verification deep dive

Retention closure requires proving end-to-end state lifecycle through save, off, and restore windows.

Concept diagram

diagram

RETENTION LIFECYCLE

save request -> state capture -> power off -> power on -> restore -> traffic resume

Metric graph

diagram

RETENTION STABILITY

restore mismatch       █████
save timing defects    ████
stable wake cycles     ███████

Metrics and artifacts to collect

retention save/restore timing report
pre/post state diff matrix
multi-cycle retention stress summary
state-loss bug trend by mode

Mini case study

A corruption issue persisted until retention checks compared multi-cycle state snapshots rather than single wake events.

Debug branches

Track save acknowledgement against actual state capture.
Validate restore completion before functional traffic resumes.
Run repeated sleep/wake cycles to expose drift.

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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