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Course contents

  • How to Use This Puzzle Bank
  • SystemVerilog Language Puzzles25
  • Difficulty Guide
  • Full Topic Map
  • Interview-Day Tips
  • OOP & Testbench Puzzles25
  • Concurrency & Timing Puzzles25
  • Randomization & Constraint Puzzles25
  • SVA Assertion Puzzles25
  • Functional Coverage Puzzles25
  • Logic & Aptitude Puzzles25
  • Scenario & Debug Puzzles25
  • Interview Prep: Puzzle Rounds5
    • Framework for Any Unseen Puzzle
    • Scenario: Testbench Hang
    • Scenario: Constraint No-Solution
    • Scenario: Vacuous Assertion Pass
    • Scenario: Coverage Not Closing
  • DV Puzzle Cheatsheet
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‹Interview Prep: Puzzle Rounds
  1. Topics
  2. DV Interview Puzzles
  3. Interview Prep: Puzzle Rounds
  4. Scenario: Constraint No-Solution

VLSI DV Interview Puzzles · All levels

Scenario: Constraint No-Solution

A transaction class randomizes reliably in directed tests, but constrained-random regressions start failing with no-solution messages after incremental feature constraints are added.

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    Scenario

    A transaction class randomizes reliably in directed tests, but constrained-random regressions start failing with no-solution messages after incremental feature constraints are added.

    What to observe

    Sharp increase in randomize failure percentage for specific scenario knobs and seed ranges.

    Common traps

    • Debugging solver internals before checking contradictory implication constraints.

    • Using broad soft constraints that silently mask intent until override order changes.

    • Disabling failing constraints globally instead of minimizing and proving satisfiability.

    Related topics

    • Back to Interview Prep

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    See also

    • Framework for Any Unseen Puzzle
    • Scenario: Coverage Not Closing