A macro remains a black box one day before floorplanning. Proceed or stop?
From PDVerse PnR Interview Handbook, part of the pdVerse Mentor Guide
Short Answer
Default answer: stop — unless you can point to the specific approved abstraction and confirm the next stage's interface requirements are actually satisfied, and the project has explicitly signed off on accepting that model state. A black box is fine on purpose — that's the whole point of abstraction, hiding internal logic you don't need to see yet. The problem isn't the black box itself; it's an unverified black box.
Technical Explanation
- The boundary of that black box still needs to be a known, complete thing: real pins (not TBD), a timing model (even if approximate, it must be declared and agreed), correct orientation/geometry, and a named owner — if any of those is still open the day before floorplanning, you don't actually have a floorplan-ready macro, you have a placeholder.
- One day before floorplanning is exactly the wrong time to discover a gap — floorplanning locks in macro placement, power ring sizing, and channel widths around this macro's assumed footprint and pins. If those assumptions are wrong, you're redoing floorplanning, not just patching a detail.
- The only legitimate "proceed" case is when the team has explicitly and knowingly accepted the risk with a real waiver (see the evidence checklist in the previous question) — silently proceeding because "we're out of time" is how late-stage floorplan rework happens.
What To Check
- Warning sign: A local stub makes linking pass but timing/interface evidence is absent.
- Inspect: Keep at least two possible causes open, then use one named object and the active mode or scenario to separate them.
- Correct: Return the handoff to the IP/library owner, obtain matched views and revision, then rerun link, structure, and timing checks.
Command Checks & Actions
- report_unbound: lists objects that did not resolve
- report_ref_libs: shows the reference libraries used for linking
- check_netlist: reports structural connectivity problems
Run the commands in order. Each line answers a separate part of the check.
Healthy, Suspicious & Hard-stop Results
- Expected: Stop unless the approved abstraction and next-stage interface requirements are complete and the project explicitly accepts that model state.
- 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. ”
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