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Course contents

  • How to Use This Course
  • Reading Path
  • CDC/RDC Glossary
  • CDC/RDC Metrics Reference
  • CDC/RDC Interview Prep
  • CDC/RDC Signoff Cheatsheet
  • Clock Domains and Failure Modes8
  • Metastability and Synchronizers16
  • CDC Protocols and Handshakes16
  • Reconvergence and Gray Coding16
  • Reset Domain Crossing16
  • Architecture and Design Rules16
  • CDC Signoff Methodology24
  • RDC Signoff16
  • Debug and Case Studies11
  • CDC and RDC Interview Prep30
    • CDC/RDC Whiteboard Framework
    • CDC/RDC Framework Drills
      • Drill Set: Single Bit
      • Drill Set: Multi-Bit and FIFO
      • Drill Set: Reset and RDC
    • Scenario: Metastability Bug
    • Scenario: Metastability Escape in Silicon Bring-up
    • Scenario: Async FIFO Pointer Mismatch
    • Scenario: Waiver Debate
    • Scenario: RDC Waiver Under Tapeout Pressure
    • CDC/RDC Interview Q&A Bank
    • CDC/RDC Interview Q&A Bank (Expanded)
  • Capstone: Sign Off a Multi-clock Peripheral4
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‹CDC/RDC Framework Drills
  1. Topics
  2. CDC & RDC
  3. CDC and RDC Interview Prep
  4. CDC/RDC Framework Drills
  5. Drill Set: Reset and RDC

Part 10 · Interview Prep · All levels

Drill Set: Reset and RDC

Six timed reset synchroniser, sequencing and RDC drills with model answer outlines.

On this page

    Reset questions test ordering arguments: assertion is easy, deassertion is the hazard, and release order is the system argument. Speak the recovery and removal mechanism before naming any circuit.

    Drill 1: why is reset deassertion the hazard, not assertion?

    Outline: Mechanism, assertion drives every flop to reset regardless of clock phase, but deassertion releases flops near a clock edge, risking recovery and removal violations that leave some flops in reset and others out. Pattern, a reset synchroniser releasing each domain synchronously. Reference: Why Deassertion Is the Hazard.

    Drill 2: draw the reset synchroniser.

    Outline: asynchronous assert into a two-flop chain in the destination clock, synchronous release at the chain output. Rules, no logic between the flops, the chain clocked by the domain it releases, reset in the synchroniser's own domain handled too. Reference: Reset Synchroniser Structure.

    Drill 3: two domains must release in order. How do you argue it?

    Outline: Assumption, the stated dependency: domain B needs domain A's clock and reset stable first. Mechanism, ordered release ranks with B held until A is out, checked as a reset-ordering violation otherwise. Evidence, the RDC structural report plus a reset-aware simulation of the ordered sequence. Reference: Release Order Across Domains.

    Drill 4: what does an RDC structural report list that a CDC report does not?

    Outline: reset-domain membership per register, asynchronous-deassertion paths without a synchroniser, reset crossings across clock domains, and ordering violations between sequenced resets. Each maps to intent rows, not just synchroniser instances. Reference: RDC Categories.

    Drill 5: flops on the same reset net release on different cycles in two blocks. One reset domain or two?

    Outline: Two: a reset domain is defined by shared release behaviour, not by the net name. Crossings between the blocks need checking even though the source net is shared. This is the intent question interviewers use to test whether you read netlists or block diagrams.

    Drill 6: simulation shows clean release, but intent was never written. Signed off?

    Outline: No. Mechanism, release simulation samples some sequences at one corner; without intent the analysis had nothing to check against, so a clean report means nothing. Evidence required, reviewed reset intent plus re-run analysis plus the simulated sequences. Level 4 adds: say which sequences simulation cannot cover, mid-operation assertion and every power-up ordering.

    Common pitfall

    Treating reset as "just another CDC input". Reset fans out everywhere and releases everything at once: the ordering and sequencing argument has no CDC equivalent, and interviewers listen for it explicitly.

    Check yourself What single sentence answers both drill 1 and drill 6?

    Assertion is self-timed but deassertion races the clock, so only a synchronised release checked against written intent counts as evidence, never a passing simulation alone.

    Related topics

    • Next: Scenario: Metastability Bug

    • Recovery and removal

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    See also

    • Drill Set: Single Bit