What evidence makes a black-box waiver defensible?
From PDVerse PnR Interview Handbook, part of the pdVerse Mentor Guide
Short Answer
A "waiver" to keep a macro as a black box isn't just a verbal agreement — it needs to produce concrete artifacts that another engineer could pick up and verify independently. ).
Technical Explanation
- ).
- It also needs a stated revision/version number and a named owner — without those, nobody downstream can tell if the black box they're using is stale relative to the real macro.
- Treat this like a checklist gate, not a trust exercise: if any of pin identity, timing treatment, required views, revision, or owner is missing, the waiver isn't defensible yet, regardless of how confident anyone feels.
- The test is repeatability — a different engineer, handed only the waiver paperwork, should be able to reconstruct exactly what assumptions were made and verify them against the real macro once it's available.
What To Check
- Warning sign: A placeholder links only because a stub was added locally.
- Inspect: Compare one named object across the related reports; the same object should tell a consistent story.
- Correct: Replace the stub with approved abstraction or return the handoff; archive the waiver only if methodology permits it.
Command Checks & Actions
- report_unbound: lists objects that did not resolve
- report_ref_libs: shows the reference libraries used for linking
Run the commands in order. Each line answers a separate part of the check.
Healthy, Suspicious & Hard-stop Results
- Expected: The interface must have approved pin identity, timing boundary treatment, logical/physical views required for the next stage, revision, and owner.
- Stop before floorplanning when required logic or timing coverage is missing or unexplained.
Common Mistake
The Trap: Do not assume the check passed just because ICC2 continued. Fix or narrowly justify the named objects, then rerun the same command.
What The Interviewer Is Testing
Be ready to explain why this matters before floorplanning.
Follow-up Question & Model Response
Model response: “I would save the report, inspect one affected object in the correct block and scenario, and make or request this correction. ”
PnR Flow Mentor Guide
Master the Physical Design Implementation Flow
Read the complete 8-chapter PnR Flow Mentor Guide free on the web — library setup through placement, clock tree synthesis, routing, chip finishing, hierarchical implementation, and ECO, all the way to stream-out.
Offline PDF Bundle
Want all 1109 questions offline?
Get the complete 4-book PDF bundle (PnR, STA, MMMC, Low Power) with a clickable table of contents - no ads, no internet needed.
Continue practising