Path Group Prioritization: Step-by-Step Walkthrough

Step-by-step analysis walkthrough

Use when you own Path Group Prioritization in a timing war room.

1. Open signoff scenario list — note worst WNS corner.

2. report_timing -max/-min on failing group.

3. Trace launch and capture clocks on critical path.

4. Check exceptions and generated clocks on path.

5. Break down cell vs net delay.

6. Compare implementation vs signoff view if delta suspicious.

7. Assign owner: RTL, synth, PD, CTS, SI.

8. Propose ECO with hold/SI check plan.

9. Run regression matrix.

10. Update closure dashboard and memo.

Artifacts to collect

• path group summary, group_policy SDC, endpoint classification report

• SDC file

• SPEF tag

• MMMC scenario list

• ECO ticket

Decision memo template

STA DECISION MEMO — Path Group Prioritization
corner/mode:
WNS/TNS:
hypothesis:
ECO:
regression:
owners: STA lead, synthesis owner, PD owner

Reference visuals

Path group map

PATH GROUPS

reg2reg   : FF -> logic -> FF     (core closure)
in2reg    : input -> FF           (interface)
reg2out   : FF -> output          (interface)
reg2cg    : FF -> clock gate      (special hold risk)

Optimize and report WNS per group — not global average only.

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