Scenario: QoR Storm: Worked Example

Worked example

Worked Example for Scenario: QoR Storm focuses on overnight WNS/TNS regression with no RTL intent change. The goal is to connect observed QoR movement to mechanism, ownership, and regression risk.

A weekly compile reports overnight WNS/TNS regression with no RTL intent change regression. Instead of random knob tuning, start by proving whether input context changed and which mechanism dominates.

Sequence under inspection

SYNTHESIS FLOW — Scenario: QoR Storm

RTL + constraints
      |
      v
elaboration + checks
      |
      v
mapping + optimization
      |
      v
QoR reports (timing/area/power)
      |
      v
incremental ECO + regression

Primary metric: overnight WNS/TNS regression with no RTL intent change

QoR storm triage board

overnight regression
  -> manifest diff
  -> isolate first drift
  -> reversible fix

1. Capture baseline and regressed artifact pair.

2. Confirm manifest parity (RTL, SDC, libs, switches).

3. Pin first metric drift and mechanism hypothesis.

4. Reproduce with scenario brief, run manifest diff, triage timeline.

5. Apply one reversible fix and run matrix regression.

Did the fix hold?

BEFORE / AFTER QOR — Scenario: QoR Storm

QoR score
  0 |                     --- target zone
 -1 |        ● regression
 -2 |             ● baseline
 -0.5|                  ● after fix
    +----------------------------------> iteration

Validate timing + area + power, not one number.

Synthesis deep dive

Interview readiness comes from repeatable QoR reasoning under pressure.

Concept diagram

INTERVIEW ANSWER SHAPE

context -> metric -> mechanism -> fix -> regression -> ownership

Metric graph

PANEL SCORING

clarity      ███████
mechanism    ██████
regression   █████

Reports and artifacts

• mock scorecard

• scenario debrief

• Q&A coverage

• framework adherence

Mini case study

Candidate improved by replacing tool-command answers with evidence-driven closure narratives.

Debug branches

• State assumptions first

• Defend option tradeoffs

• Close with rollback/regression

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

QoR storms test run-hygiene fundamentals: constraint diffs, library updates, and compile switches before speculative ECO.

Metric: overnight WNS/TNS regression with no RTL intent change