How do you audit clock groups and inter-clock relationships?
From PDVerse PnR Interview Handbook · pdVerse Mentor Guide
Short Answer
Every asynchronous, exclusive, or related declaration changes which crossings are analysed, so membership and mode scope must be reviewed.
Technical Explanation
Clock-group declarations decide which clock crossings are analyzed. One broad asynchronous or exclusive group can remove a large family of paths.
What To Check
• Warning sign: Broad asynchronous grouping removes valid timed crossings. • Inspect: Compare one named object across the related reports; the same object should tell a consistent story. • Correct: Narrow the group to verified relationships and inspect representative cross-clock paths and exceptions.
Command Checks & Actions
• report_clocks: shows clock definitions and relationships
• report_exceptions: shows timing exceptions and their scope
Run the commands in order. Each line answers a separate part of the check.Healthy, Suspicious & Hard-stop Results
• Expected: Every asynchronous, exclusive, or related declaration changes which crossings are analysed, so membership and mode scope must be reviewed. • Investigate: Broad asynchronous grouping removes valid timed crossings. • Stop before floorplanning when required logic or timing coverage is missing or unexplained. Narrow the group to verified relationships and inspect representative cross-clock paths and exceptions.
Common Mistake
Do not assume the check passed just because ICC2 continued: Broad asynchronous grouping removes valid timed crossings. 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: Broad asynchronous grouping removes valid timed crossings.
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: Narrow the group to verified relationships and inspect representative cross-clock paths and exceptions. Then I would reopen the clean checkpoint and rerun the same evidence.”
Practical Example
Symptom: Broad asynchronous grouping removes valid timed crossings. Corrective path: Narrow the group to verified relationships and inspect representative cross-clock paths and exceptions.
Continue practising