Difficulty: Hard · Puzzle 2 of 6 · Topic: Clocking Block Puzzles
For a req pulse at cycle N, at which cycle must grant be 1 for this property to pass?
interface arb_if(input bit clk);
logic req, grant;
clocking cb @(posedge clk);
default input #0 output #0;
input req, grant;
endclocking
endinterface
property p_req_to_grant;
@(vif.cb) vif.cb.req |=> ##1 vif.cb.grant;
endproperty
ap: assert property (p_req_to_grant);|=> already moves one cycle; ##1 adds another cycle.
1) Antecedent samples req at cycle N.
2) |=> shifts consequent start to cycle N+1.
3) ##1 shifts grant check to cycle N+2.
4) Property requires grant at N+2, not N+1.Answer: grant must be 1 at cycle N+2. Candidates often misread this as next-cycle (N+1) behavior.
Double-counting cycle delay is a classic `##1` interview trap.
How would you rewrite for exactly next-cycle grant expectation?