Path Group War Room: Worked Example

Worked example

Worked Example for Path Group War Room focuses on WNS per path group, endpoint owner assignment rate. The goal is to connect the observable symptom to timing mechanism, ownership, and regression risk.

A signoff run shows WNS per path group, endpoint owner assignment rate. The first review mistake is to blame implementation without checking constraints. A better review starts by pinning one critical path, proving where slack was lost, and checking whether the SDC rule is correct for Path Group War Room.

Sequence under inspection

TIMING PATH — Path Group War Room

launch FF --logic stages--> capture FF
     |                           |
  launch clock                capture clock
     |                           |
  required: arrival < capture_edge - setup
  metric: WNS per path group, endpoint owner assignment rate

War room board

PATH GROUP | WNS  | OWNER    | ACTION
reg2reg    | -80  | PD       | upsize buf
in2reg     | -40  | STA+pkg  | IO delay review
reg2cg     | -25  | CTS      | skew check

1. Capture report_timing and the relevant SDC excerpt.

2. Tag corner, mode, view, and path group.

3. Find the first cell or net that dominates critical delay.

4. Compare against path group heatmap, owner assignment sheet, daily WNS standup notes.

5. Choose one reversible ECO and write the regression matrix before editing netlist or constraints.

Did the fix work?

BEFORE / AFTER ECO — Path Group War Room

WNS (ps)
  0 |                    --- target
-50 |    ● regressed
-80 |         ● before ECO
-20 |              ● after ECO
    +-------------------------------> ECO iteration
Prove setup AND hold moved safely.

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

War rooms assign failing path groups to owning teams (RTL, synth, PD, CTS) based on delay breakdown and path class.

Metric: WNS per path group, endpoint owner assignment rate