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ncsim *N COVAUO message

Jeff000

Look into the ncsim log below, the covergroup instances, through are in the same covergoup type, do have their own names. Then why ncsim still output such *N message? 

Is there any potential risk, or how can I get rid of such *N messages?

Thanks.

ncsim: *N, COVAUO: (File: AAA.svh, Line: 45):(Time: 879220 NS + 118) Instance coverage of covergroup instance (worklib.dut_pkg::reg_XXX#(int unsigned,4294967295,0,5)::cg8365_1) inside UVM object will be accumulated with instance coverage of other covergroup instances with the same instance name (dut_pkg.reg_XXX#(int unsigned, -1, 0, 5)::cg.reg_Y_set_w_cov_1) and not separately.
ncsim: *N, COVAUO: (File: AAA.svh, Line: 45):(Time: 879220 NS + 118) Instance coverage of covergroup instance (worklib.dut_pkg::reg_XXX#(int unsigned,4294967295,0,5)::cg8327_1) inside UVM object will be accumulated with instance coverage of other covergroup instances with the same instance name (dut_pkg.reg_XXX#(int unsigned, -1, 0, 5)::cg.reg_Y_set_w_cov_2) and not separately.
ncsim: *N, COVAUO: (File: AAA.svh, Line: 45):(Time: 879220 NS + 118) Instance coverage of covergroup instance (worklib.dut_pkg::reg_XXX#(int unsigned,4294967295,0,5)::cg8129_1) inside UVM object will be accumulated with instance coverage of other covergroup instances with the same instance name (dut_pkg.reg_XXX#(int unsigned, -1, 0, 5)::cg.reg_Y_set_w_cov_3) and not separately.

  • The CUVAUO message is warning you that because your covergroup is declared in a uvm_object instead of a uvm_component, there is no fixed UVM hierarchy with which to associate the instance. This means that the simulator relies on you setting the covergroup's name via set_inst_name() if you want per-instance naming that isn't auto-generated from the class name and parameters. It also means that if you have multiple covergroups with the same name (very likely for the auto-generated names) then you won't get true instance-based coverage, you'll get a merged set of hits across all the instances of the covergroup that share the same name.

    Whether this is a problem depends entirely on your use model, which is why the message is a note, not an error.

    Try adding "-nowarn COVAUO" to suppress the message if you don't care about it, or better still, move the covergroup into a uvm_component.

  • Thanks Steve for your kind reply！

    One more question,
    In case of moving the covergroup into a uvm_component, then when I attempt to create multiple instances of that covergroup, does that mean it still needs to instantiate the corresponding uvm_componnet with distinct name so as to leverage the UVM hierarchy to identify each instance?

  • No, the simulator can figure out the good instance name based on the UVM component instance names. You should however use a coverage configuration file (CCF) and pass it to the elaboration command using the -covfile switch. In that file you need to specify a couple of options in order to be sure that all the covergroups are collected per-instance, and that the UVM hierarchy-based naming is enabled.

    set_covergroup -per_instance_default_one
    set_covergroup -new_instance_reporting

    Full details here under the set_covergroup command.

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