Many constraints target objects optimised away by synthesis. Who owns the fix?
From PDVerse PnR Interview Handbook · pdVerse Mentor Guide
Short Answer
The applied SDC must match the delivered netlist; mapping may need synthesis/STA regeneration, not local wildcard repair by PD.
Technical Explanation
Treat this as a readiness check. It should produce named objects and a result that another engineer can repeat from the same handoff.
What To Check
• Warning sign: read_sdc reports empty collections for old hierarchy paths. • Inspect: Keep at least two possible causes open, then use one named object and the active mode or scenario to separate them. • Correct: Provide exact unresolved selectors and current object evidence to the constraint producer, then reload a corrected handoff.
Command Checks & Actions
• get_cells -hierarchical <pattern>: selects design cells
• get_pins -hierarchical <pattern>: selects instance pins
• read_sdc -syntax_only <file.sdc>: parses or applies the timing constraints
Run the commands in order. Each line answers a separate part of the check.Healthy, Suspicious & Hard-stop Results
• Expected: The applied SDC must match the delivered netlist; mapping may need synthesis/STA regeneration, not local wildcard repair by PD. • Investigate: read_sdc reports empty collections for old hierarchy paths. • Stop before floorplanning when required logic or timing coverage is missing or unexplained. Provide exact unresolved selectors and current object evidence to the constraint producer, then reload a corrected handoff.
Common Mistake
Do not assume the check passed just because ICC2 continued: read_sdc reports empty collections for old hierarchy paths. 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: read_sdc reports empty collections for old hierarchy paths.
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: Provide exact unresolved selectors and current object evidence to the constraint producer, then reload a corrected handoff. Then I would reopen the clean checkpoint and rerun the same evidence.”
Practical Example
Symptom: read_sdc reports empty collections for old hierarchy paths. Corrective path: Provide exact unresolved selectors and current object evidence to the constraint producer, then reload a corrected handoff.
Continue practising