Coverage for any one of the bits in a register

Coverage
1

I’m trying to write a cover point for a 128 bit logic variable. The cover point should be hit if any one of the bits transition from 1 → 0 → 1.

I know there is a way to create cover points for each of the bits and check if their value transition from 1 → 0 → 1. But I’m not interested in coverage for all 128 bits. If any one of the bits makes the transition, then I am good.

Is there a way to do this?

2

In reply to systemvl27:

What you can do is create an array of 128 covergroups and merger the coverage together as a type

covergroup toggle_cg with function sample(bit eachbit); 
  option.per_instance = 0;
  type_option.merge_instances = 1;
  coverpoint eachbit {
  bins toggle = ( 1 => 0 => 1 };
  }
endgroup
 
toggle_cg t_cg[128]
bit [127:0] myvector;

foreach(t_cg[ii]) t_cg[ii] = new();
...
foreach(t_cg[ii]) t_cg[ii].sample(myvector[ii]);
3

In reply to dave_59:

Hi Dave,

This worked, thanks!

I think a follow up question I had was what if the transitions 1 => 0 => 1 were not happening on consecutive clocks, and the number of clocks between the transitions are not known before hand. In that case I’d have to write a cover property for each bit, and create an array of cover properties? Is there a way to merge results in that case?

4

If we want to check without bothering the no of clocks, means we have to store the previous value(upto my knowledge). and sampling the value of those three corresponding bis transition in that interested reg.

covergroup toggle_cg with function sample(bit[2:0] eachbit); 
  
  coverpoint eachbit {
  bins toggle = [3'b101];
  }
endgroup
 
toggle_cg t_cg;
bit [127:0] myvector[$];
bit [2:0] sequence;///// this is for covering 1 0 1 sequence
 
 t_cg = new();
myvector.push_back(focused_reg);/// storing the register from every txn
   if(myvector.size==3) begin
        foreach(t_cg[ii])begin
          sequence = {myvector[0][i],myvector[1][i],myvector[2][i]};
          t_cg.sample(sequence);
        end
          myvector.pop_front();/// removing the first stored value
    end