Worked example

Worked Example for Compliance & Coverage Plan focuses on spec feature coverage, compliance pass rate, waiver count. The goal is to connect the observable symptom to protocol mechanism, ownership, and regression risk.

A product workload shows spec feature coverage, compliance pass rate, waiver count. The first review mistake is to blame the whole interface. A better review starts by pinning one transaction, proving where protocol progress stopped, and checking whether the observed behavior is legal for Compliance & Coverage Plan.

Sequence under inspection

SEQUENCE — Compliance & Coverage Plan

  initiator            interconnect/PHY            target
      |  request (id) ------->  |                     |
      |                         |  forward ----------> |
      |                         |                     | work
      |                         |  <---- response ---- |
      |  <----- complete ------ |                     |
      |
   metric captured here: spec feature coverage, compliance pass rate, waiver count

Requirement-to-coverage trace

COMPLIANCE TRACE MATRIX

spec clause ──> test(s) ──> assertion(s) ──> coverage bin ──> status
  4.2.1          t_axi_07     a_resp_ok        cov_resp        PASS
  4.3.5          t_axi_12     a_order          cov_order       WAIVED (id=W3)
  4.4.0          (none)        (none)           (none)          GAP  <- find these

A gap row is the most valuable output of the plan.

1. Capture the failing waveform and transaction log.

2. Tag the request ID, address, endpoint, or lane.

3. Find the first response, retry, stall, or missing completion.

4. Compare against requirement trace matrix, coverage dashboard, waiver log.

5. Choose one reversible fix and write the regression list before editing RTL or firmware.

Did the fix work?

BEFORE / AFTER — Compliance & Coverage Plan

           failing        target
metric  |    ●              ┄┄┄┄┄┄┄
        |     \
        |      \___ ● bounded fix
        |           \
        |            ● validated
        +-------------------------------> change set
Prove the mechanism moved the metric; one good dot is not proof.

Protocol deep dive

Verification closes the gap between 'works in directed test' and 'legal under all stressed traffic'.

Concept diagram

VERIFICATION CLOSURE LOOP

spec clause -> test -> assertion -> coverage -> waiver -> signoff
                  ^                           |
                  +--------- gap found --------+

Metric graph

COVERAGE vs ESCAPE RATE

escapes
  |*
  | *
  |  *
  |   **  <- knee: more random helps
  |     ****
  +----------------> constrained-random depth

Metrics and artifacts to collect

• compliance pass rate

• coverage closure

• scoreboard mismatch rate

• assertion fire count

• waiver log

Mini case study

Block passed VIP compliance but chip failed: system test omitted cross-master ID reuse through a bridge. Scoreboard key did not include upstream port ID.

Debug branches

• If VIP pass but silicon fail, check integration assumptions.

• If scoreboard noisy, fix key (ID+port+addr).

• If coverage plateau, add compliance gap analysis not more repeats.

Senior review question

Ask: what is the first transaction that deviates, and which spec rule does it test?

Key takeaways

• Connect every protocol claim to a transaction identity and measurable metric.

• Store the artifact (waveform, log, counter) next to every signoff decision.

Common pitfalls

• Debugging timeouts without finding the first bad transaction.

• Quoting peak bus width without payload efficiency and retry overhead.

• Treating VIP compliance as a substitute for system integration replay.

Narrative walkthrough

A team sees spec feature coverage, compliance pass rate, waiver count drop 40% after a seemingly small change near Compliance & Coverage Plan.

They almost widen the interface. Instead they capture id=7 read burst and find W beats never matched AW len.