Multiple instances of covergroup using an array. How to connect "ref" signal in the class from an interface?

Coverage
, , , ,
1

Question: How do I connect the signal with “ref” keyword (in my case [63:0] flag) in the class before invoking the constructor?
Sample code for checking coverage of individual bits of 64-bit bus “flag” being set to 1:

covergroup flag_cvg (input bit [63:0] one_hot_bit_position, ref logic [63:0] flag);
  flag_cvp: coverpoint (one_hot_bit_position & flag) != 0;
  option.per_instance = 1;
endgroup : flag_cvg
class flag_cov;
  g3_vif if_g3;
  logic [63:0] flag;
  flag_cvg flag_bits[64];
  bit cov_en = 1;
  string msg_label = "flag_cov";
  function new( string name = "flag_cov", uvm_component parent = null );
    super.new( name, parent );
    **flag = if_g3.flag; // Is this allowed? I want to connect the signal from interface before invoking the constructor with new() keyword.**
    foreach(flag_bits[i])
      flag_bits[i] = new(1'b1<<i, flag);
  endfunction : new
  task main_phase(uvm_phase phase);
    forever begin
      if(cov_en) begin
	`uvm_info(msg_label,"NOW SAMPLING COVERAGE", UVM_DEBUG)
          sample_flag_cvg();
      end
    end
  endtask : main_phase
  task sample_flag_cvg();
    forever begin
      @(negedge if_g3.clkb);
      foreach(flag_bits[i])
        flag_bits[i].sample();
    end
  endtask : sample_flag_cvg
endclass : flag_cov

The interface looks like this:

interface if_g3;
  logic [63:0] flag = `FLAG_within.dout_sampled[63:0]; // DUT circuit signal connected to a logic type in interface for accessing inside the class
endinterface // if_g3
2

In reply to vinodh1180:

The procedural assignment is allowed, but does not give you the functionality you are looking for. A better idea is defining your covergroup as

overgroup flag_cvg (input bit [63:0] one_hot_bit_position) with function sample(logic [63:0] flag);
  flag_cvp: coverpoint (one_hot_bit_position & flag) != 0;
  option.per_instance = 1;
endgroup : flag_cvg

Then pass the flag value at each sample

foreach(flag_bits[i])
        flag_bits[i].sample(vif.flag);
3

In reply to dave_59:

Thanks for your suggestion Dave. So essentially my code will look like this. Am I right?

covergroup flag_cvg (input bit [63:0] one_hot_bit_position) with function sample(logic [63:0] flag);
  flag_cvp: coverpoint (one_hot_bit_position & flag) != 0;
  option.per_instance = 1;
endgroup : flag_cvg

class flag_cov;
  g3_vif if_g3;
  flag_cvg flag_bits[64];
  bit cov_en = 1;
  string msg_label = "flag_cov";
  function new( string name = "flag_cov", uvm_component parent = null );
    super.new( name, parent );
    foreach(flag_bits[i])
      flag_bits[i] = new(1'b1<<i); // Is this right?
  endfunction : new

  task main_phase(uvm_phase phase);
    forever begin
      if(cov_en) begin
	`uvm_info(msg_label,"NOW SAMPLING COVERAGE", UVM_DEBUG)
          sample_flag_cvg();
      end
    end
  endtask : main_phase

  task sample_flag_cvg();
    forever begin
      @(negedge if_g3.clkb);
      foreach(flag_bits[i])
        flag_bits[i].sample(if_g3.flag);
    end
  endtask : sample_flag_cvg
endclass : flag_cov