What does check_netlist contribute before floorplanning?
From PDVerse PnR Interview Handbook · pdVerse Mentor Guide
Short Answer
It checks structural consistency such as connectivity defects that can survive parsing and linking.
Technical Explanation
Linking only proves that ICC2 found definitions for the instances. check_netlist goes one step further and checks whether the connected design is structurally sensible before physical work begins.
What To Check
• Warning sign: The design links but contains loops, multiple drivers, unloaded or undriven objects, or empty logic. • Inspect: Start with one named object in the report and trace it to the netlist, library, or SDC statement that created it. • Correct: Classify every reported structure as a defect or reviewed intent, repair at the source when possible, and rerun.
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: It checks structural consistency such as connectivity defects that can survive parsing and linking. • Investigate: The design links but contains loops, multiple drivers, unloaded or undriven objects, or empty logic. • Stop before floorplanning when required logic or timing coverage is missing or unexplained. Classify every reported structure as a defect or reviewed intent, repair at the source when possible, and rerun.
Common Mistake
Do not assume the check passed just because ICC2 continued: The design links but contains loops, multiple drivers, unloaded or undriven objects, or empty logic. 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: The design links but contains loops, multiple drivers, unloaded or undriven objects, or empty logic.
Practical Example
Symptom: The design links but contains loops, multiple drivers, unloaded or undriven objects, or empty logic. Corrective path: Classify every reported structure as a defect or reviewed intent, repair at the source when possible, and rerun.
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