DenseChip

Low Power / UPF · All levels

Retention Register Design: Mechanism

Mechanism for Retention Register Design.

Mechanism to understand

Mechanism 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.

Retention flops preserve selected state through power collapse by copying data into retention latches powered by an always-on supply. Read this topic as an executable contract: power states, boundary policies, and transition sequencing must agree across architecture, UPF, RTL, and implementation.

  • Identify state transition where failure appears first.

  • Identify source and destination domains plus crossing policy.

  • Identify control signal origin and sequencing requirements.

Intent flow

diagram
POWER INTENT FLOW — Retention Register Design

architecture intent
      |
      v
UPF objects (domain/supply/state/strategy)
      |
      v
RTL + synthesis + PD interpretation
      |
      v
verification + signoff evidence
      |
      v
release decision

Primary metric: retention coverage %, restore mismatch count, and retained state corruption escapes

Retention datapath

diagram
RETENTION FLOP MODEL

functional FF ----save----> retention latch (AON rail)
functional FF <---restore-- retention latch

retention_supply must remain alive through collapse.

Layer responsibilities

diagram
LP OWNERSHIP LAYERS — Retention Register Design

layer                owns                          typical failure
------------------   ---------------------------   --------------------------
architecture         domain strategy               infeasible power states
UPF intent           policy objects + bindings     wrong/missing policy
implementation       LP cell insertion/routing     illegal physical behavior
verification         transition scenarios          uncovered LP bug
signoff governance   waiver + release decisions    late escape to silicon

Low-power deep dive

Isolation and retention are sequence-sensitive contracts, not static checkboxes.

Concept diagram

diagram
SEQUENCE

save -> isolate -> power-off -> power-on -> restore -> release

Metric graph

diagram
TRANSITION DEFECT MIX

polarity errors      ███████
late iso assertion   █████
restore ordering     ████

Reports and artifacts

  • isolation crossing report

  • retention list

  • save/restore timing

  • X-propagation log

Mini case study

A late isolation enable caused intermittent X leaks only on one PMU path.

Debug branches

  • Validate control polarity

  • Trace AON source

  • Replay transition waveform

Senior review question

Ask: what transition evidence proves this topic is closed, and which owner signs it?

Key takeaways

  • State transition context must accompany every low-power metric claim.

  • Intent changes require simulation, formal, and implementation re-validation.

Common pitfalls

  • Comparing results from mismatched UPF revisions.

  • Assuming static checks replace transition validation.

  • Shipping with aged waivers and unclear ownership.

Execution drill pack 1

Use this pack to rehearse low-power closure on low-power/isolation-retention/retention-register-design/mechanism: transition framing, policy ownership, implementation evidence, and release confidence.

Transition checklist

  • 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.

Review prompts

  1. Which policy object is first to deviate from intent?

  2. Which owner can apply the smallest reversible fix?

  3. What regression matrix proves no collateral damage?

  4. Which waiver conditions would still block release?

Evidence capsule

diagram
LP EVIDENCE CAPSULE 1

PATH: low-power/isolation-retention/retention-register-design/mechanism
STATE WINDOW: <from -> to>
POLICY OBJECT: <isolation / retention / shifter / switch>
OWNER: <name>
PRIMARY ARTIFACT: <report/waveform/formal result>
RELEASE DECISION: <close / bounded waiver / escalate>

Execution drill pack 2

Use this pack to rehearse low-power closure on low-power/isolation-retention/retention-register-design/mechanism: transition framing, policy ownership, implementation evidence, and release confidence.

Transition checklist

  • 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.

Review prompts

  1. Which policy object is first to deviate from intent?

  2. Which owner can apply the smallest reversible fix?

  3. What regression matrix proves no collateral damage?

  4. Which waiver conditions would still block release?

Evidence capsule

diagram
LP EVIDENCE CAPSULE 2

PATH: low-power/isolation-retention/retention-register-design/mechanism
STATE WINDOW: <from -> to>
POLICY OBJECT: <isolation / retention / shifter / switch>
OWNER: <name>
PRIMARY ARTIFACT: <report/waveform/formal result>
RELEASE DECISION: <close / bounded waiver / escalate>

Execution drill pack 3

Use this pack to rehearse low-power closure on low-power/isolation-retention/retention-register-design/mechanism: transition framing, policy ownership, implementation evidence, and release confidence.

Transition checklist

  • 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.

Review prompts

  1. Which policy object is first to deviate from intent?

  2. Which owner can apply the smallest reversible fix?

  3. What regression matrix proves no collateral damage?

  4. Which waiver conditions would still block release?

Evidence capsule

diagram
LP EVIDENCE CAPSULE 3

PATH: low-power/isolation-retention/retention-register-design/mechanism
STATE WINDOW: <from -> to>
POLICY OBJECT: <isolation / retention / shifter / switch>
OWNER: <name>
PRIMARY ARTIFACT: <report/waveform/formal result>
RELEASE DECISION: <close / bounded waiver / escalate>

Execution drill pack 4

Use this pack to rehearse low-power closure on low-power/isolation-retention/retention-register-design/mechanism: transition framing, policy ownership, implementation evidence, and release confidence.

Transition checklist

  • 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.

Review prompts

  1. Which policy object is first to deviate from intent?

  2. Which owner can apply the smallest reversible fix?

  3. What regression matrix proves no collateral damage?

  4. Which waiver conditions would still block release?

Evidence capsule

diagram
LP EVIDENCE CAPSULE 4

PATH: low-power/isolation-retention/retention-register-design/mechanism
STATE WINDOW: <from -> to>
POLICY OBJECT: <isolation / retention / shifter / switch>
OWNER: <name>
PRIMARY ARTIFACT: <report/waveform/formal result>
RELEASE DECISION: <close / bounded waiver / escalate>

Execution drill pack 5

Use this pack to rehearse low-power closure on low-power/isolation-retention/retention-register-design/mechanism: transition framing, policy ownership, implementation evidence, and release confidence.

Transition checklist

  • 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.

Review prompts

  1. Which policy object is first to deviate from intent?

  2. Which owner can apply the smallest reversible fix?

  3. What regression matrix proves no collateral damage?

  4. Which waiver conditions would still block release?

Evidence capsule

diagram
LP EVIDENCE CAPSULE 5

PATH: low-power/isolation-retention/retention-register-design/mechanism
STATE WINDOW: <from -> to>
POLICY OBJECT: <isolation / retention / shifter / switch>
OWNER: <name>
PRIMARY ARTIFACT: <report/waveform/formal result>
RELEASE DECISION: <close / bounded waiver / escalate>

Execution drill pack 6

Use this pack to rehearse low-power closure on low-power/isolation-retention/retention-register-design/mechanism: transition framing, policy ownership, implementation evidence, and release confidence.

Transition checklist

  • 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.

Review prompts

  1. Which policy object is first to deviate from intent?

  2. Which owner can apply the smallest reversible fix?

  3. What regression matrix proves no collateral damage?

  4. Which waiver conditions would still block release?

Evidence capsule

diagram
LP EVIDENCE CAPSULE 6

PATH: low-power/isolation-retention/retention-register-design/mechanism
STATE WINDOW: <from -> to>
POLICY OBJECT: <isolation / retention / shifter / switch>
OWNER: <name>
PRIMARY ARTIFACT: <report/waveform/formal result>
RELEASE DECISION: <close / bounded waiver / escalate>

Execution drill pack 7

Use this pack to rehearse low-power closure on low-power/isolation-retention/retention-register-design/mechanism: transition framing, policy ownership, implementation evidence, and release confidence.

Transition checklist

  • 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.

Review prompts

  1. Which policy object is first to deviate from intent?

  2. Which owner can apply the smallest reversible fix?

  3. What regression matrix proves no collateral damage?

  4. Which waiver conditions would still block release?

Evidence capsule

diagram
LP EVIDENCE CAPSULE 7

PATH: low-power/isolation-retention/retention-register-design/mechanism
STATE WINDOW: <from -> to>
POLICY OBJECT: <isolation / retention / shifter / switch>
OWNER: <name>
PRIMARY ARTIFACT: <report/waveform/formal result>
RELEASE DECISION: <close / bounded waiver / escalate>

Execution drill pack 8

Use this pack to rehearse low-power closure on low-power/isolation-retention/retention-register-design/mechanism: transition framing, policy ownership, implementation evidence, and release confidence.

Transition checklist

  • 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.

Review prompts

  1. Which policy object is first to deviate from intent?

  2. Which owner can apply the smallest reversible fix?

  3. What regression matrix proves no collateral damage?

  4. Which waiver conditions would still block release?

Evidence capsule

diagram
LP EVIDENCE CAPSULE 8

PATH: low-power/isolation-retention/retention-register-design/mechanism
STATE WINDOW: <from -> to>
POLICY OBJECT: <isolation / retention / shifter / switch>
OWNER: <name>
PRIMARY ARTIFACT: <report/waveform/formal result>
RELEASE DECISION: <close / bounded waiver / escalate>

Execution drill pack 9

Use this pack to rehearse low-power closure on low-power/isolation-retention/retention-register-design/mechanism: transition framing, policy ownership, implementation evidence, and release confidence.

Transition checklist

  • 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.

Review prompts

  1. Which policy object is first to deviate from intent?

  2. Which owner can apply the smallest reversible fix?

  3. What regression matrix proves no collateral damage?

  4. Which waiver conditions would still block release?

Evidence capsule

diagram
LP EVIDENCE CAPSULE 9

PATH: low-power/isolation-retention/retention-register-design/mechanism
STATE WINDOW: <from -> to>
POLICY OBJECT: <isolation / retention / shifter / switch>
OWNER: <name>
PRIMARY ARTIFACT: <report/waveform/formal result>
RELEASE DECISION: <close / bounded waiver / escalate>

Execution drill pack 10

Use this pack to rehearse low-power closure on low-power/isolation-retention/retention-register-design/mechanism: transition framing, policy ownership, implementation evidence, and release confidence.

Transition checklist

  • 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.

Review prompts

  1. Which policy object is first to deviate from intent?

  2. Which owner can apply the smallest reversible fix?

  3. What regression matrix proves no collateral damage?

  4. Which waiver conditions would still block release?

Evidence capsule

diagram
LP EVIDENCE CAPSULE 10

PATH: low-power/isolation-retention/retention-register-design/mechanism
STATE WINDOW: <from -> to>
POLICY OBJECT: <isolation / retention / shifter / switch>
OWNER: <name>
PRIMARY ARTIFACT: <report/waveform/formal result>
RELEASE DECISION: <close / bounded waiver / escalate>

Execution drill pack 11

Use this pack to rehearse low-power closure on low-power/isolation-retention/retention-register-design/mechanism: transition framing, policy ownership, implementation evidence, and release confidence.

Transition checklist

  • 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.

Review prompts

  1. Which policy object is first to deviate from intent?

  2. Which owner can apply the smallest reversible fix?

  3. What regression matrix proves no collateral damage?

  4. Which waiver conditions would still block release?

Evidence capsule

diagram
LP EVIDENCE CAPSULE 11

PATH: low-power/isolation-retention/retention-register-design/mechanism
STATE WINDOW: <from -> to>
POLICY OBJECT: <isolation / retention / shifter / switch>
OWNER: <name>
PRIMARY ARTIFACT: <report/waveform/formal result>
RELEASE DECISION: <close / bounded waiver / escalate>

Execution drill pack 12

Use this pack to rehearse low-power closure on low-power/isolation-retention/retention-register-design/mechanism: transition framing, policy ownership, implementation evidence, and release confidence.

Transition checklist

  • 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.

Review prompts

  1. Which policy object is first to deviate from intent?

  2. Which owner can apply the smallest reversible fix?

  3. What regression matrix proves no collateral damage?

  4. Which waiver conditions would still block release?

Evidence capsule

diagram
LP EVIDENCE CAPSULE 12

PATH: low-power/isolation-retention/retention-register-design/mechanism
STATE WINDOW: <from -> to>
POLICY OBJECT: <isolation / retention / shifter / switch>
OWNER: <name>
PRIMARY ARTIFACT: <report/waveform/formal result>
RELEASE DECISION: <close / bounded waiver / escalate>

Execution drill pack 13

Use this pack to rehearse low-power closure on low-power/isolation-retention/retention-register-design/mechanism: transition framing, policy ownership, implementation evidence, and release confidence.

Transition checklist

  • 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.

Review prompts

  1. Which policy object is first to deviate from intent?

  2. Which owner can apply the smallest reversible fix?

  3. What regression matrix proves no collateral damage?

  4. Which waiver conditions would still block release?

Evidence capsule

diagram
LP EVIDENCE CAPSULE 13

PATH: low-power/isolation-retention/retention-register-design/mechanism
STATE WINDOW: <from -> to>
POLICY OBJECT: <isolation / retention / shifter / switch>
OWNER: <name>
PRIMARY ARTIFACT: <report/waveform/formal result>
RELEASE DECISION: <close / bounded waiver / escalate>

Mechanism deep dive

Retention flops preserve selected state through power collapse by copying data into retention latches powered by an always-on supply.

Practice this lesson