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Q075FreeDesign Verification

Short CDC Pulse Is Not Seen in the Destination

Difficulty
Medium
Topic
Waveform Debugging
Language
SV
Interview prompt

Question

src_pulse is shorter than one destination clock period. The intended pulse bridge toggles src_toggle on every source pulse and then synchronizes that level. dst_event never appears. Rule to apply: A source pulse can be recovered only if src_toggle changes and that new level reaches the destination synchronizer. Directly sampling a short pulse is not sufficient. Which signal should be traced next to determine whether the pulse-to-toggle conversion happened?

Waveform for Short CDC Pulse Is Not Seen in the Destination. Signals: src_pulse, dst_clk_edge, dst_event. Numbered markers identify sampled columns.
Read the sampled columns from left to right, then test each choice against the stated timing rule.
Choose one

Answer choices

  1. A. src_toggle immediately after the source pulse.
  2. B. An unrelated register write strobe.
  3. C. The FIFO full flag.
  4. D. The APB select signal.
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