Datapath Debug: Inputs & Outputs

Inputs and outputs contract

Inputs & Outputs for Datapath Debug focuses on datapath QoR regression rate, functional mismatch escapes, root-cause latency. The goal is to connect observed QoR movement to mechanism, ownership, and regression risk.

Synthesis closure fails when teams optimize against different assumptions. Treat these artifacts as a signed handoff contract.

INPUTS
  - RTL tag and compile switches
  - SDC / policy constraints
  - Library and operating views
  - Optional physical estimates (topo/congestion)

OUTPUTS
  - QoR timing/area/power reports
  - transform/mapping summaries
  - owner-tagged closure memo
  - regression matrix verdict

Flow sequence

SYNTHESIS FLOW — Datapath Debug

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

Primary metric: datapath QoR regression rate, functional mismatch escapes, root-cause latency

Ownership map

OWNERSHIP MAP — Datapath Debug

artifact              owner
----------------      -----------------
compile owner       synthesis owner
timing/power owner  RTL owner
cross-team review   formal owner

Every QoR movement needs a named owner before ECO.

Synthesis deep dive

Datapath and retiming gains are only real if formal and timing remain clean.

Concept diagram

DATAPATH + RETIME

operator inference -> stage balancing -> formal proof -> QoR validation

Metric graph

FREQUENCY VS LATENCY

Fmax gain   ████████
latency cost ████

Reports and artifacts

• retiming report

• datapath inference log

• equivalence status

• latency impact sheet

Mini case study

Retiming met frequency target, but missing formal hooks delayed closure by two days.

Debug branches

• Check retime blockers

• Formal first for aggressive moves

• Compare with pipeline option

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

Datapath regressions often stem from inference misses, boundary constraints, or retiming blockers; debug flow ties symptom to transform stage.

Metric: datapath QoR regression rate, functional mismatch escapes, root-cause latency