Task inside interface. I am not getting the output from the task. please look into this

Question

This is the code, I have written

interface example_inter(input wire clock,reset);
  logic [7:0]data_load;
  logic [7:0]data_read;
  logic rd_en;
  logic wr_en;
  logic [2:0]count_value;
 logic [2:0]count;
 
  task timer(input logic [2:0]count_value, output logic [2:0] count);
      forever@(posedge clock) 
      if(reset)
      count <=0;
      else
      count <= (count < count_value)?(count+1):0;
  endtask
 
  modport generator(input data_load, rd_en,wr_en,clock,reset, output data_read);
 // modport TB(input data_read,count_value output data_load, rd_en,wr_en,clock,reset,count_out,import task timer());
endinterface
 
module primary(example_inter.generator example_if);
  logic [7:0]data_storage;
 
  always_ff @(posedge example_if.clock)	begin
    if(example_if.reset)
      data_storage <= '0;
    else
      data_storage <= example_if.data_load;
  end
  assign example_if.data_read = example_if.rd_en ? data_storage:'0;
endmodule
 
module testbench(example_inter example);
 
  initial #5
  example.timer(example.count_value, example.count);
 
  initial
    begin  
      example.rd_en =1;
      example.data_load = 8'b10101111;
      example.count_value =5;
      #10 $display("out = %b",example.data_read);
    end
 
  initial
    begin
      $dumpfile("dump.vcd"); $dumpvars();
    end
endmodule
 
module top;
 logic clock;
  logic reset;
 
  initial begin
  clock =0;
  reset =1;
  #6 reset= 0;
  end
 
  initial forever #5 clock = ~clock;
 
  example_inter if1(clock, reset);
  primary p1(if1);
  testbench test(if1);
  endmodule

Answer 1

Solution

dave_59

Forum Moderator

10898 posts

April 01, 2023 at 12:34 am

In reply to choleshaggarwal008:

A couple problems with your code.

Your simulation runs infinitely. You need to put a $finish at the time you want the simulation to end.

example.data_read will be 0 after the first clock edge at time 5. It will not have the value you have loaded until the second clock edge at time 15. You are printing its value at time 10, which is still 0.

Your task timer is modifying the count variable local to the task, not the count variable declared in the interface. Since the task never exits, the output will never be copied back to example.count. There is no reason for your task to have any arguments they way it is currently being used.

— Dave Rich, Verification Architect, Siemens EDA

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