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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 pulse bridge is intended to toggle src_toggle on each source pulse and synchronize that level, but dst_event never appears. Recovery requires src_toggle to change and the new level to reach the destination synchronizer; directly sampling the short pulse is insufficient. Which signal would you trace next to check whether 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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