What does an unresolved reference mean?
From PDVerse PnR Interview Handbook · pdVerse Mentor Guide
Short Answer
An instance requests a module or library cell definition that the active reference context cannot supply.
Technical Explanation
An unresolved reference is an instance whose definition cannot be found. ICC2 knows that something was instantiated, but it does not yet know the object that should implement it.
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. • Investigate: Linking reports an unbound object or a cell has no resolved behaviour and geometry. • Stop before floorplanning when required logic or timing coverage is missing or unexplained. Correct the cell/module name or add the approved compatible reference library, then relink and prove the unbound set is empty or justified.
Common Mistake
Do not assume the check passed just because ICC2 continued: Linking reports an unbound object or a cell has no resolved behaviour and geometry. 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: Linking reports an unbound object or a cell has no resolved behaviour and geometry.
Practical Example
Symptom: Linking reports an unbound object or a cell has no resolved behaviour and geometry. Corrective path: Correct the cell/module name or add the approved compatible reference library, then relink and prove the unbound set is empty or justified.
Continue practising