Re: gEDA: $random function

[Larry Doolittle <ldoolitt-at-NOSPAMrecycle_dot_lbl_dot_gov>]

> James Bird wrote:
> > But using icarus, how do you set the seed variable to the system 
> > clock, or some other changing variable? Are there better ways of 
> > getting a non-deterministic set of random values on successive 
> > simulations?
On Tue, Sep 28, 2004 at 08:39:41PM +1000, John Sheahan wrote:
> [chop] run a tiny perl script that [makes] a one-line file
> which is then `include 'ed

That sets the seed at compile time.  I know Icarus is pretty
quick on the compile, but if you want to set things at run
time, try using "plusargs" (and yes this too is standard, and
thus portable to other Verilog compiler/simulators, although
good luck figuring out how to set plusargs from a GUI).

[ldoolitt@recycle verilog]$ cat randseed.v 
module main;
integer i, randseed, seed, out;
initial begin
        if (!$value$plusargs("randseed=%d",  randseed)) randseed=42;
        seed = randseed;
        for (i=0; i<10; i=i+1) begin
                out = $random(seed);
                $display(out);
        end
end
endmodule
[ldoolitt@recycle verilog]$ iverilog -Wall randseed.v  
[ldoolitt@recycle verilog]$ ./a.out
-2144582656
  646214477
   38602500
 -975846261
  179453717
 -621508939
 1163993994
-1622930370
  165168915
  570580292
[ldoolitt@recycle verilog]$ ./a.out +randseed=100
-2140576256
-1836108251
 -667171664
 -202409241
 -128900368
  425654578
  459213622
 -944222065
-1713799117
-1112840069
[ldoolitt@recycle verilog]$ ./a.out +randseed=42 
-2144582656
  646214477
   38602500
 -975846261
  179453717
 -621508939
 1163993994
-1622930370
  165168915
  570580292
[ldoolitt@recycle verilog]$ SEED=`dd if=/dev/urandom bs=4 count=1 2>/dev/null | hexdump -e '"%d"'`
[ldoolitt@recycle verilog]$ echo $SEED
1381491640
[ldoolitt@recycle verilog]$ ./a.out +randseed=$SEED
 -894847851
-1706338252
-1208244625
-1075436417
 2115322364
 1231061906
  709653844
  860903270
-2135560703
 1016336249
[ldoolitt@recycle verilog]$

          - Larry