Constraint Bug Patterns: Reports & Metrics

Reports and metrics

Reports & Metrics for Constraint Bug Patterns focuses on false violation count after SDC fix, constraint audit pass rate. The goal is to connect the observable symptom to timing mechanism, ownership, and regression risk.

The job of a report is to turn false violation count after SDC fix, constraint audit pass rate into a closure decision. A single WNS number is almost never enough; you need path group breakdown, cell vs net split, and a clear gap between current slack and signoff target.

Metric movement

METRIC GRAPH — false violation count after SDC fix, constraint audit pass rate

WNS (ps)
  ^
  |                         target (0)
  |                       - - - - - - -
  |                  o after ECO + hold check
  |              o
  |         o baseline run
  |    o failing regression
  +--------------------------------------> closure iteration
    view audit     path group fix     MMMC signoff

Readout:
  - explain why WNS/TNS moved and which path group drove the change

Slack distribution

SLACK HISTOGRAM — Constraint Bug Patterns

path count
  |      ***
  |    *******
  |  ***********
  |*************  <- WNS (worst path)
  +--------------------> slack (ns)
  -0.15  0.0  0.10

Fix the left tail first; average slack misleads.

• Track false violation count after SDC fix, constraint audit pass rate by path group, corner, and analysis view.

• Report WNS/TNS and failing endpoint count together.

• Include setup and hold splits; they often diverge after ECO.

• Always store the metric next to the artifact that produced it.

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.

Reading reports