Cross coverage of two covergroups

[karandeep963]

Hi Everyone,

I am using the UVM env, in that I have two agents lets say agent1 and agen2, I want to get the cross coverage of input stimulus generated by both agents.

 

What I did till now , I have a shared seq_item.svh for both agents , so I did placed the

static cnt = 0;

class seq_item extends uvm_sequence_item;

  typedef {x,y,z} lmn_t;

  typedef {m,n,o} pqr_t;


  rand lmn_t lmn;

  rand pqr_t pqr;


covergroup cg_for_agent1:

  coverpoint a: lmn;

  coverpoint b: pqr;

end covergroup


covergroup cg_for_agent2:

  coverpoint a: lmn;

  coverpoint b: pqr;

end covergroup


covergroup cg_for_cross_ab;

  CROSS_cov: cg_for_agent1.a;cg_for_agent1.b;cg_for_agent2.a;cg_for_agent2.b

end covergroup


function post_randomise();

  if (this.get_name == pkt_for_agent1)begin

    cg_for_agent1.sample();

    cnt++;

  end


  if (this.get_name == pkt_for_agent2)begin

    cg_for_agent2.sample();

    cnt++;

  end


  if (cnt %2 == 0)begin

    cg_for_cross_ab.sample();

  end

endfunction

Now what I achieved cg_for_agent1 & cg_for_agent2 has bins covered but cg_for_cross_ab received zero bin covered.

Strange how static covergroups lost their value.

 

Apart from this, the seq_item object is created in both the agents at same time and randomized at the same time.

Please help me where I lost.

 

Thanks.

 

P.S: I am also wondering for functional coverage best technique, as per Mentor's guidelines i am doing this to achieve input test stimulus coverage , that i have sent all the vectors, please help me with any example to get it done in some other good way

 

Thanks again

[tudor.timi]

I had no idea that it's possible to cross points from two different covergroups. I've looked in the LRM and it says that in a cross, coverpoints or variables are allowed. The simulator seems to be treating the value of the coverpoint from an outer covergroup as a variable. Seeing as how you probably have 2 instances of you sequence item with different names, they cannot at the same time sample both cg_for_agent1 and cg_for_agent2 (due to the if statement). You will effectively cross the one coverpoint that does get sampled with nothing from the other one. You are probably analyzing per_type coverage and wondering, but these crosses happen on a per instance basis, so don't get tricked into thinking that the cross actually happens.

 

If you want to do such a cross you have to do it somewhere outside the sequence item, where you can get both instances.

[dave_59]

This is just hypothetical, not real SV syntax. I answered this question here: https://verificationacademy.com/forums/coverage/cross-coverage-two-covergroups

[karandeep963]

Thanks a million Dave, I will get in touch with u dere.

 

Thanks Tudor,

[karandeep963]

Hi Tudor,

 

Still stucking in the same .

 

Let me try to clear what I am doing so that you may help better.

 

I have Seq_item1 which is 8xn bits , which contains rand type def {LONG,SHORT,ZERO} packet. This packet is created and randomized in sequences, which parse it and depending on the fields of the seq_item1 generate seq_item2 which is 8 bit data sent to driver. So the enum data type visibility is for sequence only.

 

Now this seq_item1 is used in two agents , which creates the instance in their respective sequences and randomized from there.

 

As I want to see the cross of two agent what can only help is that : yes

 

Agent1 LONG Agent2 SHORT,

Agent 2 SHORT Agent1 ZERO

 

and so on.

 

So to get this I have placed the sampling event in post_randomized() function, and keep the covergroup as:

 covergroup input_coverage;
        
           BUS_PKT_SIZE:  coverpoint pkt_size_cov iff (this.get_name()== "TX_PACKET_BUS");
           
           CARD_PKT_SIZE:  coverpoint pkt_size_cov iff(this.get_name()== "CARD_PACKET");
           
           INPUT_STIMULUS_CROSS_COV:cross BUS_PKT_SIZE ,CARD_PKT_SIZE {}
  endgroup



    function void post_randomize();
        input_coverage.sample();
    endfunction         

But this cross also dissappoint me as well.

 

Please help me what wrong has happend

 

Thanks,

Karandeep

[tudor.timi]

First of all what I do is only cover transactions that I have monitored and not transactions that I have randomized. The reason is that you may create an item, randomize it, but just not send it as traffic. You could connect the monitors of both your agents to a coverage collector object and do the cross there. This way you have all info available in one place.

 

As Dave already mentioned on Verification Academy what you have to be careful with is what you cross. Is there any special relationship between the traffic coming from agent1 and agent2 (say, agent1 and agent2 both send transactions that are processed at the same time)? In this case it makes sense to do a cross because you know when to do the sampling, when both transactions come in. If you don't have any such relationship, then you don't really need a cross and it probably makes more sense to just have a separate covergroup per agent.

[karandeep963]

Well Thanks for the reply, I really appreciate the efforts.

 

Regarding the issue that only monitor those transactions which has ran, but the transactions I am talking about, randomized in the context to be used as configuring the sequence in particular as instruction to sequence.

 

About the Cross coverage sampling time for two agents: So what does INPUT STIMULUS COVERAGE means, if someone is not able to cross cover the coverage from two agent in case both generated at different times , but run in the single go transaction cycle. 

 

I really think the term INPUT STIMULUS COVERAGE is not usable as per the maturity of SV.

 

Please correct me if I am expecting anything strange.

 

Rgds,

Karandeep

[albert]

Hello,

 

I am trying to code a covergroup which looks at bins having a range between base addr and final addr.

I have a function which calculates the range of address which i want to use in my covergroup.

Basically i want to do this

memory_range : coverpoint range {bins addr[] = {[base_addr, final_addr]};}

which will be dependant on the size of the memory for which i have defined a function. The size and base_addr are read from registers inside the function.

function void calc();

bit [3:0] size;

register read to get size;
register read to get base_addr;
case(size)
4’b0000: begin
Max_addr = ‘h10000;
Final_addr= base_addr+max_addr;
covergroup.sample();
end

4’b0001: …….

endfunction

Presently when i execute this, i see only one bin getting created. The range is not taking effect.

Can anyone please suggest on how I can access the base addr and final addr from the function in my covergroup?