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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
    • Event Scheduling Puzzles
    • Race Condition Puzzles
    • Clocking Block Puzzles
    • Semaphore & Mailbox Puzzles
    • Concurrency & Timing Puzzles: Tricky Q&A
  • Randomization & Constraint Puzzles25
  • SVA Assertion Puzzles25
  • Functional Coverage Puzzles25
  • Logic & Aptitude Puzzles25
  • Scenario & Debug Puzzles25
  • Interview Prep: Puzzle Rounds5
  • DV Puzzle Cheatsheet
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‹DV Interview Puzzles
  1. Topics
  2. DV Interview Puzzles
  3. Concurrency & Timing Puzzles

VLSI DV Interview Puzzles · All levels

Concurrency & Timing Puzzles

Interview-grade puzzles on SystemVerilog scheduler regions, race analysis, clocking block semantics, and semaphore/mailbox deadlocks. Each puzzle mirrors scenarios seen in real UVM benches and focuses on cycle-accurate reasoning under pressure.

  • 5topics
  • 25lessons

Topics in this section

  1. 1Event Scheduling Puzzles6 lessons
    • Observed Assertion Sees Previous Cycle
    • Does #0 Beat NBA?
    • Chained #0 Delays vs Single NBA
    • Program Reactive Drive Lag
    • Last NBA in a Process Wins
    • Assertion Action Block Cannot Rewind Edge
  2. 2Race Condition Puzzles6 lessons
    • Competing Active Writers on x
    • Blocking Writer vs NBA Writer Same Signal
    • False Mismatch from Active Sampling
    • #0 Monitor Is Still Before NBA
    • Lost Update in Forked Counter
    • Two always_ff Writers, One Register
  3. 3Clocking Block Puzzles6 lessons
    • Why First Sample Sees Old grant
    • Interpreting |=> ##1 in Clocking Domain
    • output #1step Misses Current Edge
    • input #0 vs input #1step Snapshot
    • Raw @posedge Monitor vs @(cb) Monitor
    • Mixing Direct Drive and cb Drive
  4. 4Semaphore & Mailbox Puzzles6 lessons
    • Lock Held Across Blocking Response Wait
    • Bounded Mailbox put Deadlock
    • try_get Busy Spin at Time 0
    • Leaked Semaphore Token on Error Path
    • Two Consumers Waiting on One Mailbox
    • Deadlock-Free Request Loop with try_put/try_get
  5. 5Concurrency & Timing Puzzles: Tricky Q&A1 lesson
On this page

    What this section covers

    Interview-grade puzzles on SystemVerilog scheduler regions, race analysis, clocking block semantics, and semaphore/mailbox deadlocks. Each puzzle mirrors scenarios seen in real UVM benches and focuses on cycle-accurate reasoning under pressure.

    Topics

    Diagram
    Event Scheduling Puzzles — 6 puzzles
    Race Condition Puzzles — 6 puzzles
    Clocking Block Puzzles — 6 puzzles
    Semaphore & Mailbox Puzzles — 6 puzzles

    How to practice

    1. Open each topic and attempt every puzzle cold, writing your predicted answer first.

    2. Only then read the step-by-step solution and confirm the exact answer.

    3. Re-read the 'why candidates get it wrong' note — that is the actual interview signal.

    4. Finish with the section Q&A to rehearse explaining the rule out loud.

    Related topics

    • VLSI DV Interview Puzzles hub

    PreviousNext: Event Scheduling Puzzles

    Up next

    Up nextEvent Scheduling Puzzles

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    See also

    • How to Use This Puzzle Bank
    • SystemVerilog Language Puzzles
    • Difficulty Guide