Dynamic Power Optimization in Synthesis: Worked Example

Worked example

Worked Example for Dynamic Power Optimization in Synthesis focuses on switching power delta, clock power share, gating enable efficiency. The goal is to connect observed QoR movement to mechanism, ownership, and regression risk.

A weekly compile reports switching power delta, clock power share, gating enable efficiency regression. Instead of random knob tuning, start by proving whether input context changed and which mechanism dominates.

Sequence under inspection

SYNTHESIS FLOW — Dynamic Power Optimization in Synthesis

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

Primary metric: switching power delta, clock power share, gating enable efficiency

Dynamic power levers

switching activity
  -> gating
  -> logic restructuring
  -> operand isolation
  -> dynamic power drop

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 activity-driven power report, clock tree estimate, enable quality audit.

5. Apply one reversible fix and run matrix regression.

Did the fix hold?

BEFORE / AFTER QOR — Dynamic Power Optimization in Synthesis

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

Dynamic power reduction uses gating, restructuring, and activity-aware optimization; poor constraints can hide functional risk.

Metric: switching power delta, clock power share, gating enable efficiency