Systemverilog coverage point for multiple of n

Question

I am trying to create a bin in my coverage group to sample values that are multiple of n (where n is a constant integer in my case 15). So far, I have came up with the following code:

class rx_port;
      int unsigned rx_rates[];
      ...
      covergroup rx_cov with function sample (int unsigned rate);
           coverpoint rate{
               bins no_rate    = {0};
               bins mul_of_15  = {SOME_PRE_DEFINED_PATTERN};
           }
      endgroup;
      ....
endclass

Where SOME_PRE_DEFINED_PATTERN is an array of int from 0 to a system macro with the step of 15. I am not sure if this is the correct/best way of generating this bin. Any better suggestion?

Matthew · Accepted Answer · 2019-01-29 16:49:25Z

How about writing some helper functions:

module FIFTEEN;

  class rx_port;

    typedef enum {IS_ZERO, IS_DIVISIBLE_BY_15, IS_NOT_DIVISIBLE_BY_15} rate_type;

    function new;
      rx_cov=new;
    endfunction

    local function rate_type covergroup_helper(input int unsigned i);
      if (i==0)    return IS_ZERO;
      if (i%15==0) return IS_DIVISIBLE_BY_15;
      return IS_NOT_DIVISIBLE_BY_15;
    endfunction

    function sample (input int unsigned i);
      rx_cov.sample(covergroup_helper(i));
    endfunction

    covergroup rx_cov with function sample (rate_type rate);
      coverpoint rate;
    endgroup;
  endclass

  rx_port R = new;

  initial
    begin
      void'(R.sample(0));
      void'(R.sample(30));
      void'(R.sample(31));
      $display("coverage R.rx_cov.get_coverage= %f", R.rx_cov.get_coverage);
    end

endmodule

https://www.edaplayground.com/x/65v7

Here I've written a function that determines whether its input is divisible by 15 or not and another function which calls that to do the sampling. You could combine those functions together, but I like the division of labour in my example.

Matthew · Accepted Answer · 2019-01-29 16:48:31Z

It turns out that there is a better way:

module FIFTEEN;

  class rx_port;

    function new;
      rx_cov=new;
    endfunction

    function sample (input int unsigned i);
      rx_cov.sample(i);
    endfunction

    covergroup rx_cov with function sample (int unsigned rate);
      coverpoint rate { 
        bins IS_ZERO                = {0}; 
        bins IS_DIVISIBLE_BY_15     = {[1:$]} with ((item % 15)==0); 
        bins IS_NOT_DIVISIBLE_BY_15 = {[1:$]} with ((item % 15)!=0); 
      }
    endgroup;
  endclass

  rx_port R = new;

  initial
    begin
      void'(R.sample(0));
      void'(R.sample(30));
      void'(R.sample(31));
      $display("coverage R.rx_cov.get_coverage= %f", R.rx_cov.get_coverage);
    end

endmodule

https://www.edaplayground.com/x/3T5v

You can use with to specify bins. So

bins IS_DIVISIBLE_BY_15     = {[1:$]} with ((item % 15)==0);

gives you a bin that is hit whenever the value is divisible by 15 (but not 0) and

bins IS_NOT_DIVISIBLE_BY_15 = {[1:$]} with ((item % 15)!=0);

gives you a bin that is hit whenever the value is not divisible by 15.

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