PPA Tradeoff Playbook: Worked Example

Worked example

Worked Example for PPA Tradeoff Playbook focuses on area-power-timing Pareto points, closure runtime, regression stability. The goal is to connect observed QoR movement to mechanism, ownership, and regression risk.

A weekly compile reports area-power-timing Pareto points, closure runtime, regression stability regression. Instead of random knob tuning, start by proving whether input context changed and which mechanism dominates.

Sequence under inspection

SYNTHESIS FLOW — PPA Tradeoff Playbook

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

Primary metric: area-power-timing Pareto points, closure runtime, regression stability

PPA Pareto board

option A: timing-first
option B: balanced
option C: power-first
choose Pareto point + regression budget

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 PPA matrix, QoR comparison table, decision memo.

5. Apply one reversible fix and run matrix regression.

Did the fix hold?

BEFORE / AFTER QOR — PPA Tradeoff Playbook

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

Validate timing + area + power, not one number.

Synthesis deep dive

PPA closure is a constrained tradeoff problem, not a timing-only exercise.

Concept diagram

PPA TRIAD

timing target <-> power budget <-> area cap

Metric graph

PARETO PROGRESSION

early runs      o o
balanced point    o
over-tuned          o (risk)

Reports and artifacts

• VT mix

• leakage trend

• dynamic power trend

• PPA Pareto table

Mini case study

LVT-heavy fix recovered setup but violated leakage target; balanced VT strategy closed both.

Debug branches

• Timing-only claims need power check

• Validate hold on VT swaps

• Use Pareto memo

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

PPA closure is a constrained optimization problem: teams choose options by Pareto quality, not single-metric heroics.

Metric: area-power-timing Pareto points, closure runtime, regression stability