git:20260613.86cacb4 to git:20260721.2677e8e

---

name: sta-review

description: Read Static Timing Analysis reports, triage setup/hold/recovery/removal violations, and propose fixes (RTL pipelining, sizing, useful skew, buffer insertion). Use when the user says "STA", "timing report", "timing violation", "setup fail", "hold fail", "close timing", "WNS", "TNS".

---

# STA Review

> **Doctrine (v0.1.50):** 把修法寫進工具，而非寫進 prompt。

> Mandatory program preflight first; AI is the backstop, not the lead.

STA signoff runs in a commercial tool (PrimeTime, Tempus, OpenSTA). The

deterministic triage (5 endpoint categories → fix strategies) is now in

`programs/sta_triage_classify.py`; this skill is the wrapper that runs

it, narrates residual interpretation, and refuses to override the

program's category counts.

## Mandatory Deterministic Preflight

Before any narrative:

```bash

# 1. STA report audit (presence, WNS/TNS extraction, basic structure):

python3 plugins/vibe-ic/programs/sta_report_check.py \

--rpt <sta.rpt> --json /tmp/sta_check.json

# 2. Endpoint categorisation (5 categories + fix strategy per category):

python3 plugins/vibe-ic/programs/sta_triage_classify.py \

--endpoints-json <endpoints.json> \

--wns <wns_ns> --tns <tns_ns> \

--out-md /tmp/sta_triage.md --out-json /tmp/sta_triage.json

```

The program returns counts per category (cell_delay_limited /

net_delay_limited / logic_depth_limited / clock_skew_limited /

hold_violation) plus the fix strategy per category. **Do not author

these counts by reading the report.**

```bash

# 3. (when reviewing a PnR Tcl script) confirm the mandatory

# setup-timing-repair sequence is present, not hold-fix-only:

python3 plugins/vibe-ic/programs/pnr_timing_repair_completeness_check.py \

<pnr.tcl> --json /tmp/pnr_repair.json

```

`pnr_timing_repair_completeness_check.py` FAILs any OpenROAD PnR script

that runs only `repair_timing -hold` without `set_wire_rc` +

`repair_design` + `repair_timing -setup` (the sha256 silicon-DOA

anti-pattern). The phase3 runner already emits the full chain; this

gate is the static backstop when reviewing a hand-authored script.

## When to use

- After synthesis, after CTS, after routing, after ECO

- Any time WNS (Worst Negative Slack) or TNS (Total Negative Slack) goes positive

- When hold violations appear after routing

- Multi-corner sign-off (ss/tt/ff × low/high temp × low/high Vdd)

## Inputs

1. STA report(s) — setup + hold + recovery/removal + min-pulse-width

2. SDC constraints

3. Top violating paths (usually `-max_paths 100`)

4. Corner/mode matrix

5. Optional: RTL source for the violating module

## Workflow

1. **Categorize** every violating endpoint:

- Cell delay limited → upsize driver, Vt swap

- Net delay limited → insert buffer, reroute, shorten wire

- Logic depth limited → pipeline / restructure RTL

- Clock skew limited → useful skew, CTS re-balance

- Hold → buffer insertion on min paths

2. **Propose fix per endpoint** with an estimated slack gain

3. **Flag paths that cannot be fixed by ECO** — require RTL change

4. **Cross-corner view**: if a path fails only at one corner, adjust margin first

5. **Summarize**: WNS/TNS before → after, number of endpoints touched

## Output format

- `sta/sta_review.md`:

- Summary (WNS, TNS, #failing endpoints, corner)

- Top 20 paths with classification + fix + slack delta

- RTL change recommendations (handoff to `/rtl-repair`)

- ECO fix list (handoff to `/eco-plan`)

## Technical basis

Static timing analysis is governed by setup/hold relationships around launch/capture flops. Standard references: Bhasker & Chadha "Static Timing Analysis for Nanometer Designs". OpenSTA is the open-source signoff-class engine (https://github.com/The-OpenROAD-Project/OpenSTA).

## Handoff

- RTL change → `/rtl-repair`

- Metal-only fix → `/eco-plan`

- Power impact of sizing → `/ir-drop-triage`

## Compliance gate (mandatory)

After producing your output, save it to a file and run:

```bash

python3 plugins/vibe-ic/_shared/skill_compliance_check.py \

--requirements plugins/vibe-ic/skills/sta-review/compliance.yaml \

<your_output_file>

```

Exit 0 = PASS, exit 1 = FAIL with specific missing elements listed.

`compliance.yaml` in the corresponding skill directory enumerates

every required element of your output: section headers, metadata fields,

handoff lines, tool invocations.

**Your task is not complete until the audit returns PASS.** Missing

elements are the single largest source of skill-execution non-determinism

across different agents.

## Captured rule — PnR must run set_wire_rc + repair_design + repair_timing -setup (not hold-fix-only)

**Enforced by two programs — no longer prose judgment:**

- The full deterministic command sequence (`set_wire_rc -signal/-clock` with

NONFATAL fallbacks → `estimate_parasitics` → `repair_design` →

`repair_timing -setup` → `detailed_placement`; then post-CTS `repair_timing -hold`;

then post-global-route re-estimate + repair) is **emitted by

`programs/phase3_one_shot_runner.py`** (phase3 PnR template).

- **`programs/pnr_timing_repair_completeness_check.py`** is the static gate that

FAILs any PnR script missing that chain (the hold-only silicon-DOA shape).

Worked example (kept for context): benchmark_clean/sha256 v0.1.25 post-route

WNS = -102.76 ns, mis-blamed on the SHA round; real cause was the missing

`set_wire_rc` / `repair_design` / `repair_timing -setup` (STA optimistic,

RSZ-0089). After adding the chain (v0.1.26): WNS = +10.95 ns MET on the same RTL.

General across all OpenROAD-driven PnR — template-level, not chip-specific.

_Captured by benchmark-enhancement-capture 2026-05-28; extracted to programs in M4._