Report Timing Deep Read: Debug Playbook

Debug playbook

Debug Playbook for Report Timing Deep Read focuses on incremental delay attribution accuracy, false debug rate. The goal is to connect the observable symptom to timing mechanism, ownership, and regression risk.

STA debug is a search for the FIRST deviation, not the loudest downstream symptom. Hold failures after setup ECO are a classic example of fixing the wrong layer first.

Root-cause tree

ROOT-CAUSE TREE — Report Timing Deep Read

incremental delay attribution accuracy, false debug rate looks wrong
        |
   same netlist tag?
     /        \
   no          yes
   |            |
 view/SDC     real path or
 mismatch     constraint bug
 /    \           |
lib   SPEF    delay breakdown
diff  diff    cell vs net

1. Freeze the failing netlist tag, SDC revision, and SPEF corner.

2. Find the first constraint or delay anomaly on the critical path.

3. Map the path to launch/capture clocks and path group.

4. Classify the failure: constraint bug, view mismatch, cell delay, net delay, or SI.

5. Prove the mechanism with one reduced path or isolated scenario.

6. Patch the smallest owner-controlled fix and rerun setup, hold, and MMMC.

Review memo template

STAFF STA REVIEW MEMO — Delay Graph & Path Analysis / Report Timing Deep Read

1. Symptom
   - Watched metric: incremental delay attribution accuracy, false debug rate
   - Failing scenario: <corner/mode/view>
   - Path group: <reg2reg / in2reg / reg2out / async>
   - Database tags: <netlist, SDC, SPEF, lib>

2. Mechanism hypothesis
   - Primary mechanism: Senior STA debug reads incremental delay, sense, edge, clock domain, and exception flags on the critical path — not just slack number.
   - Competing hypothesis: <constraint bug, view mismatch, cell delay, net delay, SI>
   - Missing evidence: <report_timing, clock report, constraint trace>

3. Proposed action
   - Minimal reversible change: <SDC fix, sizing, VT swap, route, useful skew>
   - Expected metric movement: <WNS/TNS delta>
   - Regression risk: hold, other corners, SI, leakage

4. Signoff
   - Re-run artifact: annotated timing report, path viewer screenshot, constraint trace
   - Required owners: STA owner, timing closure lead
   - Final decision: ECO, waive, constraint fix, or escalate

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

Senior STA debug reads incremental delay, sense, edge, clock domain, and exception flags on the critical path — not just slack number.

Metric: incremental delay attribution accuracy, false debug rate