What does an unresolved reference mean?
From PDVerse PnR Interview Handbook, part of the pdVerse Mentor Guide
Short Answer
An unresolved reference means an instance in the netlist points to a module or library cell that the tool's currently loaded reference context simply doesn't have. ICC2 knows something was instantiated there — it just doesn't know what object is supposed to implement it.
Technical Explanation
- , a placeholder for a not-yet-available macro).
Visual Verification
Unresolved references occur when instantiated module or standard-cell master names cannot be located in loaded target libraries, creating empty black boxes that halt timing and physical optimization.
What To Check
- Warning sign: Linking reports an unbound object or a cell has no resolved behaviour and geometry.
- Inspect: Start with one named object in the report and trace it to the netlist, library, or SDC statement that created it.
- Correct: Correct the cell/module name or add the approved compatible reference library, then relink and prove the unbound set is empty or justified.
Command Checks & Actions
check_design-checks {unbound}: runs the selected design-readiness checks- report_unbound: lists objects that did not resolve
Run the commands in order. Each line answers a separate part of the check.
Healthy, Suspicious & Hard-stop Results
- Expected: An instance requests a module or library cell definition that the active reference context cannot supply.
- 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.
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