View Mismatch Triage: Debug Playbook

Debug playbook

Debug Playbook for View Mismatch Triage focuses on slack delta between views, SPEF tag mismatch count. 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 — View Mismatch Triage

slack delta between views, SPEF tag mismatch count 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 — STA Debug Playbook / View Mismatch Triage

1. Symptom
   - Watched metric: slack delta between views, SPEF tag mismatch count
   - Failing scenario: <corner/mode/view>
   - Path group: <reg2reg / in2reg / reg2out / async>
   - Database tags: <netlist, SDC, SPEF, lib>

2. Mechanism hypothesis
   - Primary mechanism: Different SPEF, RC corners, or parasitic modes between runs explain apparent regressions without any design change.
   - 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: view diff report, SPEF metadata, run comparison script
   - Required owners: STA owner, extraction owner, CAD owner
   - Final decision: ECO, waive, constraint fix, or escalate

STA deep dive

Debug hygiene separates senior STA leads from report readers.

Concept diagram

DEBUG ORDER

1. same tags?  2. constraints?  3. view?  4. real path?  5. ECO

Metric graph

ROOT CAUSE MIX (typical)

constraint bugs  ████████  35%
view mismatch    ██████    25%
real path        ██████    25%
methodology      ████      15%

Reports and artifacts

• run manifest

• SDC diff

• SPEF tag

• scenario isolation

Mini case study

Mystery regression: SPEF corner tag typo in run script — not a design bug.

Debug branches

• Manifest every run

• War room by path group

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

Different SPEF, RC corners, or parasitic modes between runs explain apparent regressions without any design change.

Metric: slack delta between views, SPEF tag mismatch count