SI Signoff Reports: Worked Example

Worked example

Worked Example for SI Signoff Reports focuses on SI-clean path %, remaining aggressor violations, signoff waiver count. The goal is to connect the observable symptom to timing mechanism, ownership, and regression risk.

A signoff run shows SI-clean path %, remaining aggressor violations, signoff waiver count. 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 SI Signoff Reports.

Sequence under inspection

TIMING PATH — SI Signoff Reports

launch FF --logic stages--> capture FF
     |                           |
  launch clock                capture clock
     |                           |
  required: arrival < capture_edge - setup
  metric: SI-clean path %, remaining aggressor violations, signoff waiver count

SI signoff summary

SI SIGNOFF DASHBOARD

delta delay violations : 12  (owner: PD)
noise violations       : 3   (owner: SI)
waivers pending        : 1   (owner: STA lead)

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 SI signoff summary, foundry SI checklist, waiver log.

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

Did the fix work?

BEFORE / AFTER ECO — SI Signoff Reports

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

STA deep dive

Coupling makes delay a function of neighbors, not just wire RC.

Concept diagram

SI ON VICTIM

victim net delay = base_RC + coupling_from_aggressors

Metric graph

DELTA DELAY ON CRITICAL PATHS

no SI   ████████  1.2ns
with SI ██████████  1.35ns  (+150ps)

Reports and artifacts

• delta delay report

• aggressor list

• noise peaks

• SI WNS delta

Mini case study

Setup fixed by upsize but SI worsened — spacing ECO on bus bits recovered margin.

Debug branches

• Re-run SI after every timing ECO

• Shield wide switching buses

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

SI signoff aggregates delta delay and noise against foundry rules and product margin; reports must map to fix ownership.

Metric: SI-clean path %, remaining aggressor violations, signoff waiver count