Save/Restore Handshake Sequencing: Software and Programmer View

Software and programmer view

Save/restore sequencing bugs look intermittent unless state snapshots and handshakes are tracked together.

What teams feel

• mode-entry regressions that are hard to reproduce

• inconsistent behavior across simulators or config profiles

• late triage loops due to weak failure classification

API and integration impact

• PMU and firmware handshake contract clarity

• power-mode API assumptions and timing envelopes

• testbench sequencing ownership and checker placement

Tooling and compile-time implications

• tool power-aware semantics and elaboration assumptions

• assertion noise versus actionable signal quality

• coverage aggregation consistency across runs

Mitigations

• standardize LPV run metadata and transition sequence capture

• gate key regressions on deterministic replay checks

• enforce boundary ownership in review templates

SOFTWARE VIEW - Save/Restore Handshake Sequencing
// prove phase ordering and boundary controls before broad waivers

Low-power verification deep dive

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

Concept diagram

RETENTION LIFECYCLE

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

Metric graph

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.

Principal LPV review addendum

Save/Restore Handshake Sequencing should be reviewed as a transition integrity system, not just isolated checks.

Use Handshake protocol compliance rate, save-to-off and restore-to-functional timing margin, and timeout escape count. as alarm and Temporal handshake checker suite with protocol assertions, timeout diagnostics, and scenario-wise latency histograms. as proof.

Retention closure requires proving save, off, and restore phases as one lifecycle with explicit handshake timing. Closure quality comes from reproducible evidence and explicit owners.