What is the difference between a dangling connection and a no-load net?
From PDVerse PnR Interview Handbook · pdVerse Mentor Guide
Short Answer
A dangling pin or port is disconnected at an interface, while a no-load net has a driver but no meaningful sink; both require context.
Technical Explanation
A dangling connection is physically disconnected at an interface. A no-load net is connected to a driver but has no useful receiver.
What To Check
• Warning sign: Unused test logic is mixed with an accidentally disconnected functional path. • Inspect: Start with one named object in the report and trace it to the netlist, library, or SDC statement that created it. • Correct: Correlate instance pins, hierarchy, and synthesis reports, then fix or waive each named object with an owner.
Command Checks & Actions
• check_netlist: reports structural connectivity problems
Run the commands in order. Each line answers a separate part of the check.Healthy, Suspicious & Hard-stop Results
• Expected: A dangling pin or port is disconnected at an interface, while a no-load net has a driver but no meaningful sink; both require context. • Investigate: Unused test logic is mixed with an accidentally disconnected functional path. • Stop before floorplanning when required logic or timing coverage is missing or unexplained. Correlate instance pins, hierarchy, and synthesis reports, then fix or waive each named object with an owner.
Common Mistake
Do not assume the check passed just because ICC2 continued: Unused test logic is mixed with an accidentally disconnected functional path. 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: Unused test logic is mixed with an accidentally disconnected functional path.
Practical Example
Symptom: Unused test logic is mixed with an accidentally disconnected functional path. Corrective path: Correlate instance pins, hierarchy, and synthesis reports, then fix or waive each named object with an owner.
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