Which files are inputs, outputs, or conditional restart data?
From PDVerse PnR Interview Handbook, part of the pdVerse Mentor Guide
Short Answer
A file's role isn't fixed by its extension — it depends entirely on what stage you're at. A routed DEF or an extracted SPEF can be the output of one run and turn right around as the input to the next restart or analysis step. For a fresh implementation start, the core handoff is a mapped netlist plus approved library, technology, timing, and (where applicable) power data — the floorplan can be generated locally or imported, scan data matters only if scan optimization is required, and activity data matters only for the power tasks you're actually running.
Technical Explanation
- A file's role isn't fixed by its extension — it depends entirely on what stage you're at. A routed DEF or an extracted SPEF can be the output of one run and turn right around as the input to the next restart or analysis step.
- For a fresh implementation start, the core handoff is a mapped netlist plus approved library, technology, timing, and (where applicable) power data — the floorplan can be generated locally or imported, scan data matters only if scan optimization is required, and activity data matters only for the power tasks you're actually running.
- As implementation progresses, the flow keeps saving databases and exporting updated netlists, physical data, extracted parasitics, and reports — full-layout formats like GDSII/OASIS belong to the later layout-assembly and manufacturing handoff, though a macro's finished layout can be an upstream reference for the block that assembles around it even while it's a downstream output for the macro itself.
- Before trusting a restart, ask what the saved database already contains internally versus what external references it still needs — and make sure everything you import corresponds to the same stage and revision. A placed checkpoint paired with a netlist from a later ECO looks fine individually but is quietly inconsistent together.
Command Checks & Actions
read_def block.defDEF is typically read in as a floorplan input at the start of a session, though a DEF can equally be an output written at a later stage -- the same format serves both roles depending on when it's used.
save_block -as blockName/labelNameWrites a labeled checkpoint -- the actual restart data this question is asking about, distinct from a true external input or a final deliverable output.
Common Mistake
The Trap: Saying GDS is always a required initial input for standard-cell placement, or treating a saved database as automatically self-contained.
Follow-up Question & Model Response
"What should a handoff manifest say beyond the path?"
Candidate Model Response: Record the role, stage, revision, producer, compatibility requirements, and intended consuming step.
Practical Example
Tapeout Scenario: A floorplanning team exports floorplan.def; place and route consumes it. Later, a route-stage export called routed.def becomes a deliverable to another tool. Both are DEF files, but their contents and expected use differ.
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