Dont-Touch & Preserve Policy: Step-by-Step Walkthrough

Step-by-step analysis walkthrough

Use when you own Dont-Touch & Preserve Policy in a synthesis closure review.

1. Confirm exact run context (RTL/SDC/lib/switch set).

2. Open section QoR dashboard and identify first drift.

3. Inspect topic-level report for mechanism evidence.

4. Determine owner and candidate reversible action.

5. Apply one change only; avoid bundled fixes.

6. Run full timing/area/power checks.

7. Validate side effects on neighboring path groups.

8. Publish memo with outcome and residual risk.

Artifacts to collect

• constraint audit, preserve list, optimization-block report

• QoR dashboard

• run manifest

• constraint diff

• regression matrix

Decision memo template

SYNTHESIS DECISION MEMO — Dont-Touch & Preserve Policy
run context:
observed metric:
hypothesis:
fix:
regression:
owners: synthesis lead, RTL owner, DFT owner

Reference visuals

Preserve policy decision tree

OBJECT MARKED preserve/dont_touch?
        |
  functional or signoff reason?
     /                \
   yes                 no
   |                   |
keep + audit       remove, re-compile

Synthesis deep dive

Constraint hygiene determines whether synthesis QoR is trustworthy.

Concept diagram

CONSTRAINT FLOW

RTL intent -> synthesis SDC -> compile checks -> QoR dashboard -> review gate

Metric graph

QOR HEALTH

constraint lint pass   ███████████████
unconstrained count    ███
policy violations      ██

Reports and artifacts

• compile QoR

• unconstrained endpoints

• constraint lint

• policy audit log

Mini case study

Nightly WNS improved but unconstrained paths jumped; strict SDC lint restored true QoR picture.

Debug branches

• Diff SDC first

• Audit dont_touch scope

• Track unconstrained trend weekly

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

dont_touch and preserve are surgical controls; overuse blocks optimization and underuse breaks intended structures such as CDC wrappers or DFT hooks.

Metric: preserved object count, blocked optimization opportunities, ECO rework