Stats

  • Locked Locked
  • Replies 2
  • Subscribers 65
  • Views 21930
  • Members are here 0
This discussion has been locked.
You can no longer post new replies to this discussion. If you have a question you can start a new discussion

SystemVerilog queue of classes

flanter

Hi all,

I try using a queue of classes but there seems to be a problem when trying to read an item from the queue. I always receives only the last item pushed into the queue... I built the following test case:

code starts here: 

module tst_case_queue_of_class ();

class cls_tmp;

    byte tmp1;
    byte tmp2;
   
endclass

cls_tmp cls_q[$];
cls_tmp in_item = new();
cls_tmp out_item= new();


initial
begin
    #10;
    in_item.tmp1 = 8'h00;
    in_item.tmp2 = 8'h01;
    cls_q.push_back(in_item);

    #10;
    in_item.tmp1 = 8'h01;
    in_item.tmp2 = 8'h02;
    cls_q.push_back(in_item);

    #10;
    in_item.tmp1 = 8'h03;
    in_item.tmp2 = 8'h04;
    cls_q.push_back(in_item);
                                
    #10;
    in_item.tmp1 = 8'h05;       
    in_item.tmp2 = 8'h06;
    cls_q.push_back(in_item);

    for (int i = 0; i < cls_q.size(); i++)
    begin
        $display("index= %1d: tmp1=0x%2h, tmp2=0x%2h",i ,cls_q[i].tmp1 ,cls_q[i].tmp2);
    end // for (int i = 0; i < cls_q.size(); i++)

    repeat(4)
    begin
        out_item = cls_q.pop_front();
        $display("q_size= %1d: tmp1=0x%2h, tmp2=0x%2h",cls_q.size() ,out_item.tmp1 ,out_item.tmp2);       
    end // repeat(4)
   
end // initial

endmodule

Results of the simulation:

index= 0: tmp1=0x05, tmp2=0x06
index= 1: tmp1=0x05, tmp2=0x06
index= 2: tmp1=0x05, tmp2=0x06
index= 3: tmp1=0x05, tmp2=0x06
q_size= 3: tmp1=0x05, tmp2=0x06
q_size= 2: tmp1=0x05, tmp2=0x06
q_size= 1: tmp1=0x05, tmp2=0x06
q_size= 0: tmp1=0x05, tmp2=0x06

code and simulation results stop here

What is the problem with queue of classes? By the way, when trying to use a queue of structs I receive a compilation error...

Thanks,

Flanter 

 

  • The problem is that you're storing the class handle in the queue. Each time you put data into the class object, it is putting it into the same class object.

    What you need to do is create a new class object for each of the data sets:

    initial begin
        in_item = new();
        #10;
        in_item.tmp1 = 8'h00;
        in_item.tmp2 = 8'h01;
        cls_q.push_back(in_item);

        in_item = new();
            #10;
        in_item.tmp1 = 8'h01;
        in_item.tmp2 = 8'h02;
        cls_q.push_back(in_item);

        ...
    end

    Tim

  • Thanks Tim!

    You are right. It solved the problem.

Community Guidelines

The Cadence Design Communities support Cadence users and technologists interacting to exchange ideas, news, technical information, and best practices to solve problems and get the most from Cadence technology. The community is open to everyone, and to provide the most value, we require participants to follow our Community Guidelines that facilitate a quality exchange of ideas and information. By accessing, contributing, using or downloading any materials from the site, you agree to be bound by the full Community Guidelines.