OCV / AOCV / POCV Mechanisms: Debug Playbook

Debug playbook

Debug Playbook for OCV / AOCV / POCV Mechanisms focuses on OCV derate %, depth-adjusted pessimism, POCV sigma contribution. The goal is to connect the observable symptom to timing mechanism, ownership, and regression risk.

STA debug is a search for the FIRST deviation, not the loudest downstream symptom. Hold failures after setup ECO are a classic example of fixing the wrong layer first.

Root-cause tree

ROOT-CAUSE TREE — OCV / AOCV / POCV Mechanisms

OCV derate %, depth-adjusted pessimism, POCV sigma contribution looks wrong
        |
   same netlist tag?
     /        \
   no          yes
   |            |
 view/SDC     real path or
 mismatch     constraint bug
 /    \           |
lib   SPEF    delay breakdown
diff  diff    cell vs net

1. Freeze the failing netlist tag, SDC revision, and SPEF corner.

2. Find the first constraint or delay anomaly on the critical path.

3. Map the path to launch/capture clocks and path group.

4. Classify the failure: constraint bug, view mismatch, cell delay, net delay, or SI.

5. Prove the mechanism with one reduced path or isolated scenario.

6. Patch the smallest owner-controlled fix and rerun setup, hold, and MMMC.

Review memo template

STAFF STA REVIEW MEMO — OCV, AOCV, POCV & Variation / OCV / AOCV / POCV Mechanisms

1. Symptom
   - Watched metric: OCV derate %, depth-adjusted pessimism, POCV sigma contribution
   - Failing scenario: <corner/mode/view>
   - Path group: <reg2reg / in2reg / reg2out / async>
   - Database tags: <netlist, SDC, SPEF, lib>

2. Mechanism hypothesis
   - Primary mechanism: Variation models add margin for on-chip delay spread; AOCV/POCV reduce over-pessimism by accounting for path depth and statistical correlation.
   - Competing hypothesis: <constraint bug, view mismatch, cell delay, net delay, SI>
   - Missing evidence: <report_timing, clock report, constraint trace>

3. Proposed action
   - Minimal reversible change: <SDC fix, sizing, VT swap, route, useful skew>
   - Expected metric movement: <WNS/TNS delta>
   - Regression risk: hold, other corners, SI, leakage

4. Signoff
   - Re-run artifact: variation report, derate table, depth histogram, POCV policy doc
   - Required owners: STA lead, library team, foundry interface
   - Final decision: ECO, waive, constraint fix, or escalate

STA deep dive

Variation policy is negotiated margin, not a tool checkbox.

Concept diagram

VARIATION STACK

nominal delay + OCV/AOCV/POCV margin = signoff delay

Metric graph

DERATE IMPACT ON WNS

OCV only     WNS -120ps
AOCV         WNS -45ps
POCV         WNS -60ps (policy dependent)

Reports and artifacts

• derate table

• AOCV depth report

• POCV sigma

• hold/setup split

Mini case study

Switched to AOCV without re-baselining hold — short paths failed min analysis.

Debug branches

• Short paths for hold

• Policy approval for derate changes

Senior review question

Ask: what corner/mode/view proves this topic is closed or failing?

Key takeaways

• State corner, mode, view, and database tag with every slack claim.

• Run setup and hold plus MMMC regression after every ECO.

Common pitfalls

• Comparing STA runs with different SPEF or SDC tags.

• Broad false_path to green-wash violations.

• Setup-only ECO without hold check.

Principal STA review addendum

Variation models add margin for on-chip delay spread; AOCV/POCV reduce over-pessimism by accounting for path depth and statistical correlation.

Metric: OCV derate %, depth-adjusted pessimism, POCV sigma contribution