Can we pass clk_en through virtual interface?

UVM
,
1

I am working on a module level UVM TB for an up/down counter.
Counter is loaded on clk if load_counter=1. But the counter is incremented/decremented on run_counter(clk_en). Clk_en is derived from clk.

On TB side, i need to validate DUT outputs, count_reached(generated on clk) and current_value(generated on run_counter).

I have a clocking block that works on clk. Since scoreboard needs run_counter(clk_en) input to run a local counter, i have passed clk_en(as run_counter) through virtual interface in driver.
The issue i observe here is:
There is an offset of 1 clk between run_counter seen by TB(print statements in monitor) and RTL.
The first run_counter(==1) seen by RTL is at 45ps where as TB debug message shows it to be at 55ps. Because of this, I see counter value mismatch .

Please let me know, what could be the issue here.

P.S: clk_en is generated in CLK_EN module on negedge of clk. I have tried to change the module locally to generate clk_en on posedge and have not seen any difference with run_counter(clk_en) on TB/RTL side.

Below is my DRIVER code:

virtual task drive();  
  @( counter_vif.counter_cb);
  if (counter_vif.reset ==1) begin
    counter_vif.counter_cb.load_counter <= req.load_counter;
    counter_vif.counter_cb.count_value  <= req.count_value;
    counter_vif.counter_cb.up_counter   <= req.up_counter;
    counter_vif.counter_cb.inc                <= req.inc;
    counter_vif.counter_cb.run_counter  <= counter_vif.clk_en;
  end //if
Endtask

Here is the MONITOR code:

virtual task run_phase(uvm_phase phase);
  super.run_phase(phase);
  forever begin
     wait(counter_vif.reset == 1);
    if (counter_vif.reset == 1) begin     
      seq_item_collected.count_value   = counter_vif.count_value;
      seq_item_collected.load_counter  = counter_vif.load_counter;
      seq_item_collected.up_counter     = counter_vif.up_counter;
      seq_item_collected.inc                  = counter_vif.inc;      
      seq_item_collected.run_counter   = counter_vif.run_counter;
           `uvm_info("MONITOR DEBUG2",$sformatf("counter_vif.load_counter  = %b, counter_vif.run_counter=%b",counter_vif.load_counter, counter_vif.run_counter), UVM_LOW)


      // sample the signals
      @(counter_vif.counter_cb);       
      // checkon run_counter-----------
      if (counter_vif.run_counter)
        seq_item_collected.current_value = counter_vif.counter_cb.current_value;
      
      // --- check on every clock-----
      seq_item_collected.count_reached = counter_vif.counter_cb.count_reached;
      trans_collected_port.write(seq_item_collected);

    end  // reset 
   end //forever
 endtask : run_phase

interface updn_counter_if(input logic clk, reset, clk_en);
  logic [ABSOLUTE_DATA_WIDTH-1:0] count_value;
  logic                           load_counter;
  logic                           up_counter;
  logic                           run_counter; 
  logic [1:0]                     inc;
  logic [ABSOLUTE_DATA_WIDTH-1:0] current_value;
  logic                           count_reached;

  clocking counter_cb @(posedge clk);
    default input #1step output #1;
    inout load_counter;
    inout count_value;
    inout up_counter;
    inout run_counter;
    inout inc;
    input current_value;
    input count_reached;  
  endclocking
endinterface
2

In reply to uvmsd:

When you say you need:

Since scoreboard needs run_counter(clk_en) input to run a local counter. <<
This is not true,
Because the scoreboard does not know anything about the timing of your control signals. You have only to extract your data in the minotor in the right way. That’s all.

3

In reply to chr_sue:
@ chr_sue
sorry, i have been phrasing my sentences vaguely.

I mean, i am sampling/collecting current_value of counter module only on run_counter, as RTL updates it on run_counter and not on every clock. Of courses i am sampling it in monitor. The code is as shown above. Scoreboard just gets it as seq_item_collected.
But, I see a difference. The run_counter in monitor and RTL are offset by 1 clk, though i am using run_counter on virtual interface.

  if (counter_vif.run_counter)
     seq_item_collected.current_value = counter_vif.counter_cb.current_value;