Difficulty: Medium · Puzzle 3 of 6 · Topic: Temporal Corner Puzzles
Property intent: when valid falls, idle must be high on the next cycle. Timeline: valid falls at C70, idle=1 at C70, idle=0 at C71. Determine the verdict.
property p_fell_idle;
@(posedge clk) $fell(valid) |=> idle;
endpropertyNon-overlapped implication checks idle one cycle after the fall event.
1) $fell(valid) is true at C70.
2) |=> shifts consequent sampling to C71.
3) idle is 0 at C71, violating requirement.Answer: FAIL - idle is not high on the required post-fall cycle.
Candidates often see idle high at the fall cycle and mistakenly declare pass.
What operator change would make the same waveform pass without changing signals?