system-verilog - Cross coverage inheriting iff clause of coverpoint

Question

I'm seeing an issue with one of my crosses inheriting the "iff" clause of one of it's constituent coverpoints.

covergroup cg @(LdReqVld_d1);
    LdReq_cp : coverpoint LdReqVld_d1 iff (!LdReqCancel);
    LdOp_cp  : coverpoint LdReqOp_d1  iff (LdReqVld_d1 && !LdReqCancel);
    LdCancel_cp : coverpoint LdReqCancel;
    CrossCancel : cross LdOp_cp, LdCancel_cp;

I'm seeing the CrossCancel is never hitting any bin with LdReqCancel == 1 even when I expect it to, and I suspect it's because the LdOp_cp is crossed with contains the iff (LdReqVld_d1 && !LdReqCancel), so the CrossCancel "secretly" has that iff guarding it too. Is this the expected behavior? And if so, how can I prevent this?

标签： system-verilog

Answer 1

A cross is technically between bins of a coverpoint, not the coverpoint itself. From the IEEE 1800-2017 SystemVerilog LRM section 19.6 Defining cross coverage:

Cross coverage of a set of N coverage points is defined as the coverage of all combinations of all bins associated with the N coverage points

So if a coverpoint bin does not get sampled because of an iff guard, the cross bin is guarded as well.