CODEWITHSUNDEEP
code-coveragesystem-verilog
Chinmay Mahato
Chinmay Mahato

Reputation: 11

Transition Cover Bins not hitting

I am sampling value from data bus, as the intended values are non-consecutive the bins are not hitting for transition coverage. While the bins are hitting standalone without transition.

Example: We want to cover transition of values for address W.

A: W | X | W | Z
D: 7 | 0 | 8 | 0

covergroup cg_ with function sample();
transtion_cp : coverpoint data {
        bins seven_repeat   = (7 [* 2]);
        bins seven_eight  = (7 => 8);
        bins eight_seven  = (8 => 7);
        bins eigth_repeat = (8 [* 2]);
        bins seven = {7};
        bins eight = {8};
  }
function new(string name, uvm_component parent);
  cg_ = new();
endfunction

virtual function void write_axi_bus(svt_axi_transaction axi_tran);
   reg [7:0] var_value;

   if(W == axi_trans.addr && (axi_trans.xact_type == svt_axi_transaction::READ || axi_trans.xact_type == svt_axi_transaction::WRITE)) begin
     var_value = axi_trans.data[0][7:0];    
   end
   cg_.sample(var_value);
endfunction

Is anything wrong with the above code, as currently the transition bins are not hitting. But I see the standalone bins are hitting i.e (7,8). Let me know if I am missing anything in above code.

Upvotes: 1

Views: 351

Answers (1)

toolic
toolic

Reputation: 62227

You override the built-in sample function using with sample, but you do not specify a signal list to pass to it. When you call sample in the write_axi_bus function, you pass var_value, but var_value is not being used for coverage sampling. Refer to IEEE Std 1800-2017, section 19.3 Defining the coverage model: covergroup.

Even if var_value were used, it might not have the values you want to sample. When the write_axi_bus function is called, var_value is 1st set to x (unknown) in the reg declaration. Only when the if condition is true do you set var_value to a non-x value.

The value of data is being used for coverage, which means you need to set it to the expected value when sample is called.

Upvotes: 0

Related Questions