Synthesis & Logic Optimization · All levels

ECO Regression Discipline: Debug Playbook

Debug Playbook for ECO Regression Discipline.

Debug playbook

Debug Playbook for ECO Regression Discipline focuses on post-ECO regressions caught, corner coverage, signoff approval latency. The goal is to connect observed QoR movement to mechanism, ownership, and regression risk.

Synthesis debug finds the first causal drift, not the loudest downstream symptom.

Root-cause tree

diagram

ROOT-CAUSE TREE — ECO Regression Discipline

post-ECO regressions caught, corner coverage, signoff approval latency regressed
        |
   same RTL/constraints tag?
     /              \
   no                yes
   |                  |
input drift      transform side-effect
 /    \             /         \
SDC    libs      mapping      physical estimate
diff   diff      choice       mismatch

Freeze baseline and regressed run manifests.
Verify RTL/SDC/library deltas before transform tuning.
Classify issue: constraints, mapping choice, physical estimate, or ECO side effect.
Pick one minimal reversible change.
Re-run full timing/area/power checks with ownership signoff.

Review memo template

diagram

STAFF SYNTHESIS REVIEW MEMO — Incremental & ECO Synthesis / ECO Regression Discipline

1. Symptom
   - Watched metric: post-ECO regressions caught, corner coverage, signoff approval latency
   - Affected compile run: <tag/build ID>
   - Impacted path/class: <critical group / power lane / area lane>
   - Database tags: <RTL, SDC, libs, switches>

2. Mechanism hypothesis
   - Primary mechanism: Regression discipline prevents late-stage surprises by enforcing setup/hold, power, and equivalence checks after every ECO wave.
   - Competing hypothesis: <constraint drift, mapping choice, physical estimate mismatch>
   - Missing evidence: <report diff, dashboard trend, ownership board>

3. Proposed action
   - Minimal reversible change: <constraint patch, compile knob, ECO cell move>
   - Expected movement: <timing / area / power delta>
   - Regression risk: hold, power spike, leakage drift, formal mismatch

4. Signoff
   - Re-run artifact: regression matrix, signoff checklist, release memo
   - Required owners: timing closure lead, verification owner, program owner
   - Final decision: merge, rollback, or escalate

Synthesis deep dive

Incremental and ECO synthesis protect schedule only with strict regression discipline.

Concept diagram

diagram

INCREMENTAL ECO LOOP

identify delta -> localized compile -> patch -> regression -> release

Metric graph

diagram

ECO CYCLE TIME

full compile      ███████████
incremental       █████

Reports and artifacts

incremental reuse
ECO patch list
LEC status
regression matrix

Mini case study

Localized compile cut turnaround 40%, but skipped LEC caused rollback.

Debug branches

Reuse ratio is not enough
Patch locality check
Always include equivalence hooks

Senior review question

Ask: what evidence proves this QoR move is real and stable?

Key takeaways

State exact run context (RTL, SDC, libs, switches) with every QoR claim.
Re-run timing, area, and power regressions after each synthesis ECO.

Common pitfalls

Comparing runs with mismatched constraints or library views.
Timing-only fixes that violate power or area budgets.
Skipping equivalence checks after structural changes.

Principal synthesis review addendum

Regression discipline prevents late-stage surprises by enforcing setup/hold, power, and equivalence checks after every ECO wave.

Metric: post-ECO regressions caught, corner coverage, signoff approval latency

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