Cross coverage across multiple covergroup

Coverage
, ,
1

I have a question about a cross coverage among multiple covergroups. Below is the example code which I found in a web article[*1].

class A;
  rand bit[3:0] var1;
 
  covergroup cgA;
    option.per_instance = 1;
    coverpoint var1 {
          bins each[16] = {[0:$]};
    }
  endgroup
 
  function new ();
      cgA = new;
  endfunction
endclass

class B extends A;
  rand bit[3:0] var2;
 
  covergroup cgB(); 
    option.per_instance = 1;
    coverpoint var2 {
          bins all = {[0:$]};
      }
    cross cgA.var1, var2; 
  endgroup
 
  function new ();
    super.new();
    cgB = new;
  endfunction
endclass

There is a cross coverage which takes bins from different covergroups:

cross cgA.var1, var2;

    for (int i = 0;i < 5; i++) begin
      a.randomize();
      b.randomize();
      $display ("a.var1=0x%0h b.var1=0x%0h b.var2=0x%0h", a.var1, b.var1, b.var2);
      a.cgA.sample();  // step 1
      b.cgA.sample();  // step 2
      b.cgB.sample();  // step 3
    end

The sampling timing for cgA and cgB are different in the code.

My question: is it okey to think that the cross coverage is computed when “b.cgB.sample(); // step 3” is executed and the value of cg.A is last sampled value for cgA (i.e. “step 2”)?
I could not find the statement to define as such in LRM.

Regards

[*1] https://www.chipverify.com/blog/inheritance-of-covergroups

2

In reply to tsb_matumoto:

Cross coverage between different covergroups is not allowed by the currently SystemVerilog standard. Some tools have experimented with it, but you are right to point out that the sampling semantics between the two covergroups is a major hurdle in making it work.

3

In reply to dave_59:

Thank you for the information.
I learned crossing covergroups is not a part of LRM yet.