Interview Drills for Retention Register Design focuses on retention coverage %, restore mismatch count, and retained state corruption escapes. The goal is to link observed behavior to power-intent mechanism, ownership, and release risk.
PROMPT
You see retention coverage %, restore mismatch count, and retained state corruption escapes on Retention Register Design. Walk through root cause and release decision.
STRONG ANSWER
1. Names failing state transition and domains.
2. Explains Retention flops preserve selected state through power collapse by copying data into retention latches powered by an always-on supply.
3. Requests retention list, save/restore controller spec, and retention verification report.
4. Proposes bounded fix and regression matrix.
WEAK ANSWER
Jumps to generic UPF edits without transition timeline, ownership, or signoff evidence.RETENTION FLOP MODEL
functional FF ----save----> retention latch (AON rail)
functional FF <---restore-- retention latch
retention_supply must remain alive through collapse.ROOT-CAUSE TREE — Retention Register Design
retention coverage %, restore mismatch count, and retained state corruption escapes regressed
|
reproducible in same sequence?
/ \
no yes
| |
stimulus drift intent mismatch or
testbench issue implementation bug
/ \ |
power checker crossing/strategy audit
state model + waveform timelineIsolation and retention are sequence-sensitive contracts, not static checkboxes.
SEQUENCE
save -> isolate -> power-off -> power-on -> restore -> releaseTRANSITION DEFECT MIX
polarity errors ███████
late iso assertion █████
restore ordering ████isolation crossing report
retention list
save/restore timing
X-propagation log
A late isolation enable caused intermittent X leaks only on one PMU path.
Validate control polarity
Trace AON source
Replay transition waveform
Ask: what transition evidence proves this topic is closed, and which owner signs it?
State transition context must accompany every low-power metric claim.
Intent changes require simulation, formal, and implementation re-validation.
Comparing results from mismatched UPF revisions.
Assuming static checks replace transition validation.
Shipping with aged waivers and unclear ownership.
Use this pack to rehearse low-power closure on low-power/isolation-retention/retention-register-design/interview: transition framing, policy ownership, implementation evidence, and release confidence.
State transition explicitly named with legal source/target states.
Crossing and domain ownership are mapped and agreed.
Policy controls are traced to always-on source logic.
Waveform bookmarks align controls with state timestamps.
Which policy object is first to deviate from intent?
Which owner can apply the smallest reversible fix?
What regression matrix proves no collateral damage?
Which waiver conditions would still block release?
LP EVIDENCE CAPSULE 1
PATH: low-power/isolation-retention/retention-register-design/interview
STATE WINDOW: <from -> to>
POLICY OBJECT: <isolation / retention / shifter / switch>
OWNER: <name>
PRIMARY ARTIFACT: <report/waveform/formal result>
RELEASE DECISION: <close / bounded waiver / escalate>Use this pack to rehearse low-power closure on low-power/isolation-retention/retention-register-design/interview: transition framing, policy ownership, implementation evidence, and release confidence.
State transition explicitly named with legal source/target states.
Crossing and domain ownership are mapped and agreed.
Policy controls are traced to always-on source logic.
Waveform bookmarks align controls with state timestamps.
Which policy object is first to deviate from intent?
Which owner can apply the smallest reversible fix?
What regression matrix proves no collateral damage?
Which waiver conditions would still block release?
LP EVIDENCE CAPSULE 2
PATH: low-power/isolation-retention/retention-register-design/interview
STATE WINDOW: <from -> to>
POLICY OBJECT: <isolation / retention / shifter / switch>
OWNER: <name>
PRIMARY ARTIFACT: <report/waveform/formal result>
RELEASE DECISION: <close / bounded waiver / escalate>Use this pack to rehearse low-power closure on low-power/isolation-retention/retention-register-design/interview: transition framing, policy ownership, implementation evidence, and release confidence.
State transition explicitly named with legal source/target states.
Crossing and domain ownership are mapped and agreed.
Policy controls are traced to always-on source logic.
Waveform bookmarks align controls with state timestamps.
Which policy object is first to deviate from intent?
Which owner can apply the smallest reversible fix?
What regression matrix proves no collateral damage?
Which waiver conditions would still block release?
LP EVIDENCE CAPSULE 3
PATH: low-power/isolation-retention/retention-register-design/interview
STATE WINDOW: <from -> to>
POLICY OBJECT: <isolation / retention / shifter / switch>
OWNER: <name>
PRIMARY ARTIFACT: <report/waveform/formal result>
RELEASE DECISION: <close / bounded waiver / escalate>Use this pack to rehearse low-power closure on low-power/isolation-retention/retention-register-design/interview: transition framing, policy ownership, implementation evidence, and release confidence.
State transition explicitly named with legal source/target states.
Crossing and domain ownership are mapped and agreed.
Policy controls are traced to always-on source logic.
Waveform bookmarks align controls with state timestamps.
Which policy object is first to deviate from intent?
Which owner can apply the smallest reversible fix?
What regression matrix proves no collateral damage?
Which waiver conditions would still block release?
LP EVIDENCE CAPSULE 4
PATH: low-power/isolation-retention/retention-register-design/interview
STATE WINDOW: <from -> to>
POLICY OBJECT: <isolation / retention / shifter / switch>
OWNER: <name>
PRIMARY ARTIFACT: <report/waveform/formal result>
RELEASE DECISION: <close / bounded waiver / escalate>Use this pack to rehearse low-power closure on low-power/isolation-retention/retention-register-design/interview: transition framing, policy ownership, implementation evidence, and release confidence.
State transition explicitly named with legal source/target states.
Crossing and domain ownership are mapped and agreed.
Policy controls are traced to always-on source logic.
Waveform bookmarks align controls with state timestamps.
Which policy object is first to deviate from intent?
Which owner can apply the smallest reversible fix?
What regression matrix proves no collateral damage?
Which waiver conditions would still block release?
LP EVIDENCE CAPSULE 5
PATH: low-power/isolation-retention/retention-register-design/interview
STATE WINDOW: <from -> to>
POLICY OBJECT: <isolation / retention / shifter / switch>
OWNER: <name>
PRIMARY ARTIFACT: <report/waveform/formal result>
RELEASE DECISION: <close / bounded waiver / escalate>Use this pack to rehearse low-power closure on low-power/isolation-retention/retention-register-design/interview: transition framing, policy ownership, implementation evidence, and release confidence.
State transition explicitly named with legal source/target states.
Crossing and domain ownership are mapped and agreed.
Policy controls are traced to always-on source logic.
Waveform bookmarks align controls with state timestamps.
Which policy object is first to deviate from intent?
Which owner can apply the smallest reversible fix?
What regression matrix proves no collateral damage?
Which waiver conditions would still block release?
LP EVIDENCE CAPSULE 6
PATH: low-power/isolation-retention/retention-register-design/interview
STATE WINDOW: <from -> to>
POLICY OBJECT: <isolation / retention / shifter / switch>
OWNER: <name>
PRIMARY ARTIFACT: <report/waveform/formal result>
RELEASE DECISION: <close / bounded waiver / escalate>Use this pack to rehearse low-power closure on low-power/isolation-retention/retention-register-design/interview: transition framing, policy ownership, implementation evidence, and release confidence.
State transition explicitly named with legal source/target states.
Crossing and domain ownership are mapped and agreed.
Policy controls are traced to always-on source logic.
Waveform bookmarks align controls with state timestamps.
Which policy object is first to deviate from intent?
Which owner can apply the smallest reversible fix?
What regression matrix proves no collateral damage?
Which waiver conditions would still block release?
LP EVIDENCE CAPSULE 7
PATH: low-power/isolation-retention/retention-register-design/interview
STATE WINDOW: <from -> to>
POLICY OBJECT: <isolation / retention / shifter / switch>
OWNER: <name>
PRIMARY ARTIFACT: <report/waveform/formal result>
RELEASE DECISION: <close / bounded waiver / escalate>Use this pack to rehearse low-power closure on low-power/isolation-retention/retention-register-design/interview: transition framing, policy ownership, implementation evidence, and release confidence.
State transition explicitly named with legal source/target states.
Crossing and domain ownership are mapped and agreed.
Policy controls are traced to always-on source logic.
Waveform bookmarks align controls with state timestamps.
Which policy object is first to deviate from intent?
Which owner can apply the smallest reversible fix?
What regression matrix proves no collateral damage?
Which waiver conditions would still block release?
LP EVIDENCE CAPSULE 8
PATH: low-power/isolation-retention/retention-register-design/interview
STATE WINDOW: <from -> to>
POLICY OBJECT: <isolation / retention / shifter / switch>
OWNER: <name>
PRIMARY ARTIFACT: <report/waveform/formal result>
RELEASE DECISION: <close / bounded waiver / escalate>Use this pack to rehearse low-power closure on low-power/isolation-retention/retention-register-design/interview: transition framing, policy ownership, implementation evidence, and release confidence.
State transition explicitly named with legal source/target states.
Crossing and domain ownership are mapped and agreed.
Policy controls are traced to always-on source logic.
Waveform bookmarks align controls with state timestamps.
Which policy object is first to deviate from intent?
Which owner can apply the smallest reversible fix?
What regression matrix proves no collateral damage?
Which waiver conditions would still block release?
LP EVIDENCE CAPSULE 9
PATH: low-power/isolation-retention/retention-register-design/interview
STATE WINDOW: <from -> to>
POLICY OBJECT: <isolation / retention / shifter / switch>
OWNER: <name>
PRIMARY ARTIFACT: <report/waveform/formal result>
RELEASE DECISION: <close / bounded waiver / escalate>Use this pack to rehearse low-power closure on low-power/isolation-retention/retention-register-design/interview: transition framing, policy ownership, implementation evidence, and release confidence.
State transition explicitly named with legal source/target states.
Crossing and domain ownership are mapped and agreed.
Policy controls are traced to always-on source logic.
Waveform bookmarks align controls with state timestamps.
Which policy object is first to deviate from intent?
Which owner can apply the smallest reversible fix?
What regression matrix proves no collateral damage?
Which waiver conditions would still block release?
LP EVIDENCE CAPSULE 10
PATH: low-power/isolation-retention/retention-register-design/interview
STATE WINDOW: <from -> to>
POLICY OBJECT: <isolation / retention / shifter / switch>
OWNER: <name>
PRIMARY ARTIFACT: <report/waveform/formal result>
RELEASE DECISION: <close / bounded waiver / escalate>Use this pack to rehearse low-power closure on low-power/isolation-retention/retention-register-design/interview: transition framing, policy ownership, implementation evidence, and release confidence.
State transition explicitly named with legal source/target states.
Crossing and domain ownership are mapped and agreed.
Policy controls are traced to always-on source logic.
Waveform bookmarks align controls with state timestamps.
Which policy object is first to deviate from intent?
Which owner can apply the smallest reversible fix?
What regression matrix proves no collateral damage?
Which waiver conditions would still block release?
LP EVIDENCE CAPSULE 11
PATH: low-power/isolation-retention/retention-register-design/interview
STATE WINDOW: <from -> to>
POLICY OBJECT: <isolation / retention / shifter / switch>
OWNER: <name>
PRIMARY ARTIFACT: <report/waveform/formal result>
RELEASE DECISION: <close / bounded waiver / escalate>Use this pack to rehearse low-power closure on low-power/isolation-retention/retention-register-design/interview: transition framing, policy ownership, implementation evidence, and release confidence.
State transition explicitly named with legal source/target states.
Crossing and domain ownership are mapped and agreed.
Policy controls are traced to always-on source logic.
Waveform bookmarks align controls with state timestamps.
Which policy object is first to deviate from intent?
Which owner can apply the smallest reversible fix?
What regression matrix proves no collateral damage?
Which waiver conditions would still block release?
LP EVIDENCE CAPSULE 12
PATH: low-power/isolation-retention/retention-register-design/interview
STATE WINDOW: <from -> to>
POLICY OBJECT: <isolation / retention / shifter / switch>
OWNER: <name>
PRIMARY ARTIFACT: <report/waveform/formal result>
RELEASE DECISION: <close / bounded waiver / escalate>Use this pack to rehearse low-power closure on low-power/isolation-retention/retention-register-design/interview: transition framing, policy ownership, implementation evidence, and release confidence.
State transition explicitly named with legal source/target states.
Crossing and domain ownership are mapped and agreed.
Policy controls are traced to always-on source logic.
Waveform bookmarks align controls with state timestamps.
Which policy object is first to deviate from intent?
Which owner can apply the smallest reversible fix?
What regression matrix proves no collateral damage?
Which waiver conditions would still block release?
LP EVIDENCE CAPSULE 13
PATH: low-power/isolation-retention/retention-register-design/interview
STATE WINDOW: <from -> to>
POLICY OBJECT: <isolation / retention / shifter / switch>
OWNER: <name>
PRIMARY ARTIFACT: <report/waveform/formal result>
RELEASE DECISION: <close / bounded waiver / escalate>Retention flops preserve selected state through power collapse by copying data into retention latches powered by an always-on supply.
Metric: retention coverage %, restore mismatch count, and retained state corruption escapes
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