Why should input delay not be applied indiscriminately to clock ports?
From PDVerse PnR Interview Handbook · pdVerse Mentor Guide
Short Answer
A clock port defines timing reference behaviour and is not ordinary launched data; bulk get_ports * selectors can impose nonsensical data delay.
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: A blanket input-delay command constrains clocks and resets as data. • Inspect: Compare one named object across the related reports; the same object should tell a consistent story. • Correct: Select intended data ports explicitly and review collection membership before applying delays.
Command Checks & Actions
• get_ports *: selects boundary ports
• report_ports -input_delay [get_ports *]: shows boundary constraints and electrical assumptions
Run the commands in order. Each line answers a separate part of the check.Healthy, Suspicious & Hard-stop Results
• Expected: A clock port defines timing reference behaviour and is not ordinary launched data; bulk get_ports * selectors can impose nonsensical data delay. • Investigate: A blanket input-delay command constrains clocks and resets as data. • Stop before floorplanning when required logic or timing coverage is missing or unexplained. Select intended data ports explicitly and review collection membership before applying delays.
Common Mistake
Do not assume the check passed just because ICC2 continued: A blanket input-delay command constrains clocks and resets as data. 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 blanket input-delay command constrains clocks and resets as data.
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: Select intended data ports explicitly and review collection membership before applying delays. Then I would reopen the clean checkpoint and rerun the same evidence.”
Practical Example
Symptom: A blanket input-delay command constrains clocks and resets as data. Corrective path: Select intended data ports explicitly and review collection membership before applying delays.
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