How do you verify output loads?
From PDVerse PnR Interview Handbook · pdVerse Mentor Guide
Short Answer
Correlate load values with receiver and package assumptions, units, modes, and min/max analysis needs.
Technical Explanation
Output load represents what the block must drive outside its boundary. A realistic value comes from the receiver and package assumptions, with the correct capacitance unit.
What To Check
• Warning sign: Loads are missing, scaled incorrectly, or copied uniformly across unlike interfaces. • Inspect: Compare one named object across the related reports; the same object should tell a consistent story. • Correct: Correct the producing interface model and inspect design-rule and timing behaviour at representative outputs.
Command Checks & Actions
• report_ports -design_rule [get_ports *]: shows boundary constraints and electrical assumptions
• report_user_units: shows the units ICC2 uses when reading and printing values
Run the commands in order. Each line answers a separate part of the check.Healthy, Suspicious & Hard-stop Results
• Expected: Correlate load values with receiver and package assumptions, units, modes, and min/max analysis needs. • Investigate: Loads are missing, scaled incorrectly, or copied uniformly across unlike interfaces. • Stop before floorplanning when required logic or timing coverage is missing or unexplained. Correct the producing interface model and inspect design-rule and timing behaviour at representative outputs.
Common Mistake
Do not assume the check passed just because ICC2 continued: Loads are missing, scaled incorrectly, or copied uniformly across unlike interfaces. 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: Loads are missing, scaled incorrectly, or copied uniformly across unlike interfaces.
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: Correct the producing interface model and inspect design-rule and timing behaviour at representative outputs. Then I would reopen the clean checkpoint and rerun the same evidence.”
Practical Example
Symptom: Loads are missing, scaled incorrectly, or copied uniformly across unlike interfaces. Corrective path: Correct the producing interface model and inspect design-rule and timing behaviour at representative outputs.
Continue practising