Report Timing Deep Read: Mechanism

Mechanism to understand

Mechanism for Report Timing Deep Read focuses on incremental delay attribution accuracy, false debug rate. The goal is to connect the observable symptom to timing mechanism, ownership, and regression risk.

Senior STA debug reads incremental delay, sense, edge, clock domain, and exception flags on the critical path — not just slack number. Think of STA as a signed contract between constraints, parasitics, and implementation — slack is the measurable outcome.

• Identify launch and capture clocks on the failing path.

• Identify path group: reg2reg, in2reg, reg2out, or async.

• Identify whether setup, hold, or both fail in the scenario.

Layered view

STA CLOSURE FLOW — Report Timing Deep Read

constraints (SDC)
        |
        v
timing graph (cell + net delays)
        |
        v
MMMC scenarios (corner x mode x view)
        |
        v
variation + SI adjustments
        |
        v
slack (WNS/TNS) -> ECO -> regression

Debug rule: always state corner, mode, view, and database tag with slack.

Critical path annotation

REPORT TIMING LINE (what to read)

 (rise) 0.12  U234/Z (AND2)     <- incremental delay
        0.45  net foo/bar       <- net delay + fanout
 (fall) 0.08  U567/D (DFF)      <- sense and edge matter
 clock: clk_main rise@500ps      <- launch/capture clocks

Read incremental delay, not just total slack.

Layer responsibilities

STA OWNERSHIP LAYERS — Report Timing Deep Read

layer              owns                         failure mode
----------------   --------------------------   ---------------------
constraints        clocks, IO, exceptions       false violations
implementation     cells, nets, placement       real path delay
extraction         SPEF/RC corners              view mismatch
signoff policy     derate, MMMC matrix          margin disputes
closure           ECO order, regression        fix breaks other corner

STA deep dive

Slack is a path story — read the graph, not just the number.

Concept diagram

TIMING GRAPH

FF --cell-- logic --net-- logic --cell-- FF
launch                              capture

Metric graph

SLACK TAIL

paths |    ***
      |  *******
      |*********  <- fix WNS first

Reports and artifacts

• WNS/TNS

• path slack histogram

• cell vs net %

• path group summary

Mini case study

WNS -90ps but 80% net delay on one congested route — PD route fix beat upsizing three cells.

Debug branches

• Cell-heavy -> sizing/VT

• Net-heavy -> route/layer

• Check launch/capture clocks

Senior review question

Ask: what corner/mode/view proves this topic is closed or failing?

Key takeaways

• State corner, mode, view, and database tag with every slack claim.

• Run setup and hold plus MMMC regression after every ECO.

Common pitfalls

• Comparing STA runs with different SPEF or SDC tags.

• Broad false_path to green-wash violations.

• Setup-only ECO without hold check.

Mechanism deep dive

Senior STA debug reads incremental delay, sense, edge, clock domain, and exception flags on the critical path — not just slack number.