Path Group Prioritization: Inputs & Outputs

Inputs and outputs contract

Inputs & Outputs for Path Group Prioritization focuses on WNS by path group, reg2reg vs in2reg vs reg2out slack. The goal is to connect the observable symptom to timing mechanism, ownership, and regression risk.

Treat these as a signed interface contract. Ambiguity here is the single biggest source of wasted integration weeks, because two teams debug against different assumptions.

INPUTS
  - SDC (clocks, IO delays, exceptions)
  - Liberty libraries per corner
  - SPEF/parasitics and RC corner
  - MMMC scenario definition

OUTPUTS
  - WNS/TNS reports per scenario
  - path group summaries
  - constraint audit / waiver log
  - signoff closure memo

Timing path sequence

TIMING PATH — Path Group Prioritization

launch FF --logic stages--> capture FF
     |                           |
  launch clock                capture clock
     |                           |
  required: arrival < capture_edge - setup
  metric: WNS by path group, reg2reg vs in2reg vs reg2out slack

Ownership map

OWNERSHIP MAP — Path Group Prioritization

artifact              owner
----------------      -----------------
timing report       STA lead
SDC/constraint      synthesis owner
implementation      PD owner

Every WNS cluster needs a named owner before ECO.

STA deep dive

Slack is a path story — read the graph, not just the number.

Concept diagram

TIMING GRAPH

FF --cell-- logic --net-- logic --cell-- FF
launch                              capture

Metric graph

SLACK TAIL

paths |    ***
      |  *******
      |*********  <- fix WNS first

Reports and artifacts

• WNS/TNS

• path slack histogram

• cell vs net %

• path group summary

Mini case study

WNS -90ps but 80% net delay on one congested route — PD route fix beat upsizing three cells.

Debug branches

• Cell-heavy -> sizing/VT

• Net-heavy -> route/layer

• Check launch/capture clocks

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

Path groups classify timing intent so optimization and debug focus on the paths that matter for signoff and product modes.

Metric: WNS by path group, reg2reg vs in2reg vs reg2out slack