VLSI DV Interview Puzzles · All levels

Sequence and Operator

Property intent: from one start cycle, both sub-sequences must match: req ##1 gnt and req ##2 done. Timeline: C40 start=1 req=1, C41 gnt=1, C42 d1. Determine the verdict.

Puzzle

Difficulty: Medium · Puzzle 4 of 6 · Topic: Sequence Puzzles

Property intent: from one start cycle, both sub-sequences must match: req ##1 gnt and req ##2 done. Timeline: C40 start=1 req=1, C41 gnt=1, C42 done=1. Determine the verdict.

Code

systemverilog

property p_seq_and;
  @(posedge clk) start |-> ((req ##1 gnt) and (req ##2 done));
endproperty

Hint

For sequence and, both sequences share a start but may end at different cycles.

Step-by-step solution

diagram

1) start triggers and launches both sequence branches at C40.
2) First branch req ##1 gnt matches (req at C40, gnt at C41).
3) Second branch req ##2 done matches (req at C40, done at C42).
4) Both branches match, so the and composition matches.

Answer

Answer: PASS - both sequence branches succeed from the same start cycle, satisfying the sequence and operator.

Why candidates get it wrong

A common mistake is assuming both branches must end on the same cycle (that is intersect, not and).

Interviewer follow-up

If done moved to C43, which part would fail first and why?

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