Jump to content

Possible bug in uvm_create_random_seed()


Recommended Posts

In uvm_create_random_seed() (in uvm_misc.svh) is the following code that returns different seed values for a given {type_id, inst_id}:

  seed_map.seed_table[type_id] = seed_map.seed_table[type_id]+seed_map.count[type_id]; 
  seed_map.count[type_id]++;

  return seed_map.seed_table[type_id];

The problem is that this can return a seed of 0, which is not a valid seed value to srandom().

Am I missing something, or is this really a bug?

Thanks,

Jeff Schroeder
 

Link to comment
Share on other sites

  • 2 years later...
  • 1 month later...
On 3/12/2022 at 3:27 PM, dave_59 said:

This is a warning from one particular tool, not the UVM code. srandom(seed) is a SystemVerilog language feature and there is no restriction on value of the seed 

Dave, much thanks for your reply!

I have tried, it turns out as you said to be a warning by tools.

My demo code in EDA Playground: pass 0 to process.srandom();

process srandom - EDA Playground

class touseprocess;
   process proc = process::self();
  
  function procsrandom(int unsigned seed);
    proc.srandom(seed);
    return $urandom;
  endfunction
endclass


program test;
  touseprocess up;
  integer x, y, z;
  initial begin
    up = new();
    fork //set a seed at the start of a thread
      begin 
        x = up.procsrandom(0);
        $display("x = %0d", x);
      end

      //set a seed during a thread
      begin
        y = up.procsrandom(200);
        $display("y = %0d", y);
      end

      // draw 2 values from the thread RNG
      begin
        z = $urandom + $urandom;
        $display("z = %0d", z);
      end
    join
  end
  
endprogram

When i use vcs, i will get the warning, but will not when using other simulators.

Edited by Yesire-Lincoln
Insert code snippet directly
Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...