Which logical counts should be reconciled?
From PDVerse PnR Interview Handbook · pdVerse Mentor Guide
Short Answer
Compare ports, hierarchical cells, sequential cells, combinational cells, memories/macros, nets, and references with the synthesis handoff.
Technical Explanation
Counts are fingerprints, not proofs. A large mismatch quickly tells you that the loaded design, hierarchy, or revision may differ from the handoff.
What To Check
• Warning sign: A large count mismatch reveals the wrong top, a missing hierarchy, or different optimisation settings. • Inspect: Start with one named object in the report and trace it to the netlist, library, or SDC statement that created it. • Correct: Identify the first mismatching class and resolve the revision or import cause before timing review.
Command Checks & Actions
• sizeof_collection [get_ports *]: counts exactly the objects returned by a selector
• sizeof_collection [get_cells -hierarchical *]: counts exactly the objects returned by a selector
• sizeof_collection [get_nets -hierarchical *]: counts exactly the objects returned by a selector
Run the commands in order. Each line answers a separate part of the check.Healthy, Suspicious & Hard-stop Results
• Expected: Compare ports, hierarchical cells, sequential cells, combinational cells, memories/macros, nets, and references with the synthesis handoff. • Investigate: A large count mismatch reveals the wrong top, a missing hierarchy, or different optimisation settings. • Stop before floorplanning when required logic or timing coverage is missing or unexplained. Identify the first mismatching class and resolve the revision or import cause before timing review.
Common Mistake
Do not assume the check passed just because ICC2 continued: A large count mismatch reveals the wrong top, a missing hierarchy, or different optimisation settings. 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 large count mismatch reveals the wrong top, a missing hierarchy, or different optimisation settings.
Practical Example
Symptom: A large count mismatch reveals the wrong top, a missing hierarchy, or different optimisation settings. Corrective path: Identify the first mismatching class and resolve the revision or import cause before timing review.
Continue practising