Conditional creation of covergroup

Question

I have 2 heterogenous cores which utilise the same tb environment. Hence I have created 2 instances of coverage class. However I need to create & sample covergroup based on the core. How can I do so?

I have tried this, however getting error that sample() function can only be called on covergroup instances created.

class my_agent extends uvm_agent;
cov_collector[NUM_CORES];
  
function void build phase(uvm_phase phase);
super.build_phase(phase);
  for(int i=0;i<NUM_CORES; i++)
  begin
  cov_collector=my_cov_collector::type_id::create($psprintf("cov_collector[%0d]",i),this);
  cov_collector.core=i;
  end
endfunction
   

class my_cov_collector extends uvm_monitor;
int core;

covergroup core0;
endgroup

covergroup core1;
endgroup

function new();
super.new();
if(core==0) begin core0=new(); end
if(core==1) begin core1=new(); end
endfunction

task sample();
if(core==0) begin core0.sample(); end
if(core==1) begin core1.sample(); end
endtask

It seems to me that issue is core variable is being assigned value in build phase. However new function is invoked before that & it considers default value of core as 0 & hence only creates core0 covergroups in both instances.

Could anyone suggest a solution?

Answer 1

The issue you're facing is related to the fact that the new() function is being called before the core variable is assigned a value in the build_phase. To address this, you should initialize the core variable in the new() function itself.

Here's a modified version of your code:

class my_agent extends uvm_agent;
  my_cov_collector cov_collector[NUM_CORES];

  function void build_phase(uvm_phase phase);
    super.build_phase(phase);
    for (int i = 0; i < NUM_CORES; i++) begin
      cov_collector[i] = my_cov_collector::type_id::create($psprintf("cov_collector[%0d]", i), this);
      cov_collector[i].core = i;
    end
  endfunction
endclass

class my_cov_collector extends uvm_monitor;
  int core;
  covergroup core0;
  endgroup

  covergroup core1;
  endgroup

  function new(string name = "my_cov_collector");
    super.new(name);
  endfunction

  function void build_phase(uvm_phase phase);
    super.build_phase(phase);

    // Initialize covergroups based on the core value
    if (core == 0) begin
      core0 = new;
    end
    if (core == 1) begin
      core1 = new;
    end
  endfunction

  task sample();
    if (core == 0) begin
      core0.sample();
    end
    if (core == 1) begin
      core1.sample();
    end
  endtask
endclass

In this the core variable is initialized with its default value in the new() function. Later, during the build_phase, you update the core0 and core1 covergroups based on the value of the core variable. This should resolve the issue you were facing.