write the sv driver code to generate and drive 'valid' from TB side so that it follows the below -mentioned protocol and conditions. please note that there is no transaction or packet given here.

Question

A testbench and a DUT interact with each other.For Interaction with the DUT, the testbench sends a 'valid' signal to the DUT. For Every such 'valid', the DUT will later send an 'ack' signal. Both 'valid' and 'ack' are 1 clock wide pulses, they are active high signals and synchronous to the same clock.

The maximum possible rate of 'valid' is 1 'valid' in 3 consective clock cycles. The maximum possible rate of 'ack' is also 1 'ack' in 3 consective clock cycles. As DUT may take variable amount of time to process the valid sent by testbench the 'ack' from DUT can get delayed. Every 'valid' for which the DUT is yet to send back the 'ack' treated as 'outstanding_valid'

if the number of such outstanding valid exceed 32, then the bench can't drive additional 'valid' till the number of the outstanding valid comes below 32.

please help me in this.

Answer 1

ben@SystemVerilog.us

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2656 posts

August 22, 2022 at 2:22 pm

In reply to Subbi Reddy:
Below is untested code. I changed your requirements because they were inconsistent.
I explain the design approach in the comments.
https://www.edaplayground.com/x/hvkw

 /* Testbench sends a 'valid' signal to the DUT. 
   For Every such 'valid', the DUT will later send an 'ack' signal. 
   Both 'valid' and 'ack' are 1 clock wide pulses, synchronous to the same clock.
   The maximum (changed to minimum) rate of 'valid' is 1 'valid' in 3 consective clock cycles. 
   The maximum (Changed to minimum response time) 
      possible rate of 'ack' is also 1 'ack' in 3 consective clock cycles. 
   DUT may take variable amount of time to process the valid; 'ack' can get delayed. 
   Every 'valid' for which the DUT is yet to send back the 'ack' treated as 'outstanding_valid'
   if the number of such outstanding valid exceed 32, then the bench can't drive additional 'valid' till the number of the outstanding valid comes below 32.*/
module top;  
    timeunit 1ns;  timeprecision 100ps;    
    `include "uvm_macros.svh"   import uvm_pkg::*;
    bit clk, valid, ack, sent, reset_n;
    int vld_count; // valid count 
    let max_delay=10; 
    default clocking @(posedge clk); endclocking
    initial forever #10 clk = !clk;
    // Three tasks 
    // 1) Send valid task 
    //    - Randomided delay followed by send of valid followed by a 2 cycle delay
    // 2) Count tracking, increment if sent, decrement if ack 
    // 3) Controller to manage the send based on the vld_count and sent
 
    // Send the valid 
    task automatic send_valid();
        int delay;
          if (!randomize(delay) with 
              {delay inside {[0:10]};}
              ) `uvm_error("MYERR", "This is a randomize error");
          repeat(delay) @(posedge clk); // 
          valid <= 1; @(posedge clk) valid<=0; 
          repeat(2) @(posedge clk); 
      sent <=1; @(posedge clk) sent <= 0; 
    endtask: send_valid
 
    // Valid Count tracking 
    always_ff @(posedge clk) begin: the_count
      if(sent && !ack) vld_count <= vld_count +1; 
      if(ack && !sent) vld_count <= vld_count -1; 
      am_count: assert(vld_count >=0 && vld_count <33);
    end: the_count
 
    always @(posedge clk) begin: controller 
      send_valid(); 
      @(sent) if(vld_count==32) wait(vld_count < 32);    
    end: controller 
 
    initial begin
      repeat(100) begin 
        @(posedge clk);  
        if(valid) begin 
            repeat(4) @(posedge clk);
            ack <= 1; 
            @(posedge clk) ack <= 0; 
        end 
       $finish;
       end
    end 
  endmodule

Ben Cohen
http://www.systemverilog.us/
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