Functional constraints were loaded into test mode. What evidence exposes it?

Short Answer

This is a debugging exercise, and the way you catch it is by comparing what a scenario actually contains against what it should contain for its declared mode — a mislabeled scenario usually leaves fingerprints across several categories at once. Start with scenario-mode association: does report_scenarios or the equivalent actually show test mode pointing at the SDC file/constraints intended for functional mode? This is often the most direct smoking gun — a filename or mode tag mismatch.

Technical Explanation

• Check the clocks active in that scenario — functional mode and test mode frequently run at different frequencies (test/scan clocks are often much slower, or use a different source entirely), so if test mode shows functional-frequency clocks, that's a strong tell.
• Look at case analysis — test mode typically has specific scan-enable/test-mode select pins forced to particular values; if those case-analysis settings are missing or contradict what functional mode would set, the constraints clearly weren't written for this mode.
• , via ATE constraints), is another red flag.
• , certain CDC paths, certain mode-exclusive muxes) shouldn't appear as exceptions in a genuinely test-mode-specific SDC, since test mode often exercises paths that functional mode treats as false.
• Package this as a repeatable diff: pull the constraint sets for both modes side by side (clocks, case analysis, I/O delays, exceptions) and look for functional-mode fingerprints sitting where test-mode fingerprints should be — a single named discrepancy in any of these categories is usually enough to prove the mix-up.

What To Check

• Warning sign: Test analysis inherits functional constants or functional interfaces disappear.
• Inspect: Keep at least two possible causes open, then use one named object and the active mode or scenario to separate them.
• Correct: Reload constraints in their intended mode context and compare mode-specific reports before proceeding.

Healthy, Suspicious & Hard-stop Results

• Expected: Compare scenario-mode associations, clocks, case analysis, I/O delays, and exception membership across modes.
• Stop before floorplanning when required logic or timing coverage is missing or unexplained.

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. ”