Help on using DistValInt

[Alvin Manlapat]

*Hi,

I was trying to use DistValInt in my code but I keep getting one output value.

I’ve decraled the variable inside the PROCESS as:

variable rndx  : RandomPType;

variable tmp_val : integer;

then I’ve used it as:

rndx.InitSeed(SEED);

tmp_val := rndx.DistValInt(((1,1),(2,5),(3,3),(4,1)));

I changed the value of SEED a couple of times (e.g. 1234, 555, 5567) but I was always getting 1 as result for tmp_val. Did I miss something in my equations?

Thank you in advance for help and suggestions.

[Jim Lewis]

Hi Alvin,
You need to show more code. I can’t tell how many times you call DistValInt. What I would expect to see is:

process
  variable rndx  : RandomPType;
  variable tmp_val : integer;
begin
rndx.InitSeed(SEED);  -- do one time.

loop
  tmp_val := rndx.DistValInt(((1,1),(2,5),(3,3),(4,1)));
  -- do something
end loop ;

One key point is that the seed is a state variable and is only set one time at the beginning. A given seed will always produce the same sequence – this is important for test stability. WRT trying different seeds and always getting a 1 first – this is possible since you have a 25% chance of it happening. Although several generate the same initial value, it is likely that they will generate a different sequence.

Have you looked at RandomPkg_user_guide.pdf?

Best,
Jim

[Alvin Manlapat]

Hi Jim,

I’ve tried something similar to your example code and now it produced the results that I was expecting. 

counts := (0,0,0,0);
for i in 0 to 100 loop
  tmp_val := rndx.DistValInt(((1,1),(2,5),(3,3),(4,1)));
  case (tmp_val) is
    when 1      => counts(0) := counts(0)+1; 
    when 2      => counts(1) := counts(1)+1; 
    when 3      => counts(2) := counts(2)+1; 
    when 4      => counts(3) := counts(3)+1; 
    when others => counts    := counts;
  end case;    
end loop;

report "counts: " & to_string(counts(0)) & ","
                  & to_string(counts(1)) & ","
                  & to_string(counts(2)) & ","
                  & to_string(counts(3));

I got "Note: counts: 8,54,27,12" in my simulation run.

Yesterday I did not execute the rndx.DistValInt() multiple times and I only tested a few SEED values to initialize my random variable and I think that was the reason why I did not observe the generation of tmp_val properly.

Thanks a lot for your help,

Alvin

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