When can a black box be intentional?
From PDVerse PnR Interview Handbook · pdVerse Mentor Guide
Short Answer
A black box is acceptable only when the methodology deliberately abstracts its internals and still provides a controlled interface for timing and implementation.
Technical Explanation
A black box hides internal logic on purpose. Its boundary still needs known pins, models, revision, and ownership; otherwise it is simply a missing part of the handoff.
What To Check
• Warning sign: A missing macro model is labelled intentional without evidence of pins, timing boundaries, or ownership. • Inspect: Start with one named object in the report and trace it to the netlist, library, or SDC statement that created it. • Correct: Obtain the approved abstract views or return the handoff; record the intended abstraction and its interface limits.
Command Checks & Actions
• report_unbound: lists objects that did not resolve
• 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: A black box is acceptable only when the methodology deliberately abstracts its internals and still provides a controlled interface for timing and implementation. • Investigate: A missing macro model is labelled intentional without evidence of pins, timing boundaries, or ownership. • Stop before floorplanning when required logic or timing coverage is missing or unexplained. Obtain the approved abstract views or return the handoff; record the intended abstraction and its interface limits.
Common Mistake
Do not assume the check passed just because ICC2 continued: A missing macro model is labelled intentional without evidence of pins, timing boundaries, or ownership. 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: A missing macro model is labelled intentional without evidence of pins, timing boundaries, or ownership.
Practical Example
Symptom: A missing macro model is labelled intentional without evidence of pins, timing boundaries, or ownership. Corrective path: Obtain the approved abstract views or return the handoff; record the intended abstraction and its interface limits.
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