How do you test whether ICC2 and PrimeTime use different libraries?
From PDVerse PnR Interview Handbook, part of the pdVerse Mentor Guide
Short Answer
A library mismatch between two tools is one of the sneakiest correlation bugs, because both tools can report plausible-looking numbers while quietly reading different characterization data underneath. lib` files across environments if search paths differ.
Technical Explanation
- 81V) or has one silently defaulted to a "typical" condition because a corner assignment didn't stick?
- Verify cell identity at the instance level — the same instance name can, in principle, resolve to a different physical/timing view if reference-library search order differs between the two setups; don't assume
U123means the same cell everywhere. - Confirm scenario mapping: each tool's mode+corner+scenario combination has to line up one-to-one, otherwise you're comparing timing computed under genuinely different assumptions and blaming the tools for it.
- Only after libraries, PVT, cell identity, and scenario mapping are all confirmed identical should you start comparing path arithmetic — at that point any remaining delta is a real correlation issue worth digging into, not an artifact of mismatched inputs.
What To Check
- Warning sign: The same instance has materially different cell delay in the two tools.
- Inspect: Keep at least two possible causes open, then use one named object and the active mode or scenario to separate them.
- Correct: Align the approved model sets and contexts through the library/STA owners, then compare one fully expanded path.
Command Checks & Actions
- report_ref_libs: shows the reference libraries used for linking
- report_pvt: shows process, voltage, and temperature assignments
- report_scenarios: shows the MCMM scenario matrix and analysis status
Run the commands in order. Each line answers a separate part of the check.
Healthy, Suspicious & Hard-stop Results
- Expected: Compare resolved library versions, PVT, operating conditions, cell identities, and scenario mapping before path arithmetic.
- 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.
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. ”
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