Hi,
i’m struggling with a tricky randomization issue.
With this example code
class rand_C
randc int rand_a;
rand int rand_b;
constraint a_c {rand_a inside {0,1,2,3,4,5,6,7,8,9,10};}
constraint b_c {rand_b inside {4, 8, 10};}
constraint a_b {rand_a < rand_b ; solve rand_b before rand_a]}
endclass : rand_C
This a wrong piece of code, I know, because randc variables are always solved before any other (LRM 18.5.10); but i was wondering if there’s a way to avoid this LRM limitation.
In reply to dave_59:
I just want to randomize rand_b to find the max value (1st step) for the rand_a randomization (2nd step).
In reply to alexkidd84:
You have conflicting requirements. You cannot cycle through all the values of rand_a if you choose rand_b first. In table below, after the 6th step, there is no number you can choose without repeating a value before exhausting other unused numbers.
| Step | rand_a | rand_b |
|---|---|---|
| 1 | 3 | 4 |
| 2 | 2 | 8 |
| 3 | 1 | 10 |
| 4 | 0 | 4 |
| 5 | 4 | 8 |
| 6 | ??? | 4 |
In reply to dave_59:
In reply to alexkidd84:
You have conflicting requirements. You cannot cycle through all the values of rand_a if you choose rand_b first. In table below, after the 6th step, there is no number you can choose without repeating a value before exhausting other unused numbers.
Step rand_a rand_b 1 3 4 2 2 8 3 1 10 4 0 4 5 4 8 6 ??? 4 Ok, I forgot another requirement. The randomization of rand_b should be done only at first time of class randomization. So the table should be:
Step rand_a rand_b 1 3 4 2 2 4 3 0 4 6 1 4
In reply to alexkidd84:
That’s a significant piece of missing information.
Remove the solve before construct from your example
You can explicitly call randomize(rand_b), the subsequently call randomize(rand_a)
Or you can add a post_randomize() function to turn off rand_b.rand_mode(0).
In reply to dave_59:
I made something similiar to what you wrote, but I can’t realize how it will be with post_randomize() function:
randC c1;
if( first iteration) begin
c1.rand_b.rand_mode(1);
c1.rand_a.constraint_mode(0);
c1.randomize(rand_b)
end
c1.rand_b.rand_mode(0);
c1.rand_a.constraint_mode(1);
c1.randomize(rand_a);