How do you confirm the correct top module and netlist revision?
From PDVerse PnR Interview Handbook, part of the pdVerse Mentor Guide
Short Answer
The top module is the boundary ICC2 believes it's implementing — get this wrong and every count, report, and timing number downstream can look perfectly reasonable while describing the wrong design. Confirming it means matching four things against the handoff record and synthesis summary: the current block, the expected top name, the hierarchy structure, and the cell/instance inventory.
Technical Explanation
- Treat a mismatch here as a hard stop, not a minor note — nothing you check after this point is trustworthy until the top and revision are confirmed correct.
Visual Verification
Top-level design audits cross-verify the active database container against synthesis handoff manifests to prevent optimizing obsolete netlist revisions or incorrect design variants.
What To Check
- Warning sign: Reports look plausible but describe an older top or a sibling block.
- Inspect: Start with one named object in the report and trace it to the netlist, library, or SDC statement that created it.
- Correct: Open and select the approved block, then repeat identity and inventory checks before applying constraints.
Command Checks & Actions
- current_block: confirms the active design block
- get_blocks *: lists available design blocks
- sizeof_collection [get_cells -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: The current block, expected top name, hierarchy, and inventory must agree with the handoff record and synthesis summary.
- 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.
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