Covergroup instance warning

SystemVerilog
,
1

I have following code for covergroup inside a class:
class wdt_apb_trans extends apb_trans;
rand TransType tr_type;

covergroup apb_extra_cov;             // line number 21
    coverpoint tr_type;
endgroup

function new;
this.apb_extra_cov = new();
endfunction

endclass

Now during simulation I am getting following warning

ncsim: W,COVDCG: (File: /**/_trans.sv, Line: 21):(Time: 363242 NS + 4) Covergroup instance (worklib.WdtPkg::wdt_apb_trans::apb_extra_cov@5841), is garbage collected. Its instance coverage will not be reported separately and instead accumulated into corresponding type-coverage (WdtPkg.wdt_apb_trans::apb_extra_cov).

Can somebody please tell me how o get this working without above warning ?

Thanks,

2

In reply to MonaliDeshmukh:

Hi Monali,

You may be creating wdt_apb_trans transaction multiple times, if you want to get separate coverage reports for each instance, use per_instance option,

covergroup apb_extra_cov;
  // Separate report for each instance
  option.per_instance = 1;
  coverpoint tr_type;
endgroup
3

In reply to mayurkubavat:

Hi Mayur,

Thanks for reply.

I have tried to set per_instance ( option.per_instance = 1;) but still I am getting same warning

4

In reply to MonaliDeshmukh:

Use “nchelp ncsim COVDCG” for more information on warning.

For the snippet I’m unable to simulate the warning.


covergroup cg ;
...
endgroup
cg cg_inst1 = new ;
cg cg_inst2 = new ;
  initial begin
     #5 cg_inst1 = null;  // warning will be thrown
     #5 cg_inst2 = null;  // warning will not be thrown
  end
5

In reply to mayurkubavat:

This warning should be ok but I didn’t understand actual cause of this warning.

Here is my code

File 1: —

typedef enum {VAL_RD, VALA_RD, LD_RD, CLRI_WR_CCCC, CLRI_WR_OTHER, MISC} TransType;

class wdt_apb_trans extends apb_trans;
rand TransType tr_type;

covergroup apb_extra_cov; // line number 21
    coverpoint tr_type;
endgroup

function new;
    this.apb_extra_cov = new();
endfunction

endclass

file 2 :-- Cover group is sampled in this class

class wdt_irq_seq extends apb_sequence;
`uvm_object_utils(wdt_irq_seq)

function new (string name = “wdt”);
super.new(name);
endfunction

virtual task extra_traffic;
forever begin
wdt_apb_trans tr = new();
tr.apb_extra_cov.sample();
endtask

endclass

6

In reply to MonaliDeshmukh:

The problem might be here,

virtual task extra_traffic;
  forever begin
    wdt_apb_trans tr = new();
    tr.apb_extra_cov.sample();
    //..
  end
endtask

When creating covergroup in a forever loop, each time when new class object is constructed, previous object/covergroup will be deallocated. And according to help option, tool will only warn first time.

I think moving covergroup from class to module or creating it only once(for e.g, have separated subscriber object to implement covergroup) will remove the warning.