SI ECO Fix Order: Worked Example

Worked example

Worked Example for SI ECO Fix Order focuses on post-ECO SI WNS recovery, reroute count, spacing violations cleared. The goal is to connect the observable symptom to timing mechanism, ownership, and regression risk.

A signoff run shows post-ECO SI WNS recovery, reroute count, spacing violations cleared. 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 ECO Fix Order.

Sequence under inspection

TIMING PATH — SI ECO Fix Order

launch FF --logic stages--> capture FF
     |                           |
  launch clock                capture clock
     |                           |
  required: arrival < capture_edge - setup
  metric: post-ECO SI WNS recovery, reroute count, spacing violations cleared

SI fix priority

SI ECO ORDER
1. spacing / shield on worst aggressors
2. victim upsize (if delta delay)
3. reroute victim to quiet layer
4. re-run SI + setup + hold matrix

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 ECO change list, before/after SI report, regression matrix.

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

Did the fix work?

BEFORE / AFTER ECO — SI ECO Fix Order

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 fixes use spacing, shielding, sizing, and reroute; order matters because a setup fix can worsen hold or noise elsewhere.

Metric: post-ECO SI WNS recovery, reroute count, spacing violations cleared