Specman on-the-fly generation for multiple constrained items

Question

I have this multiple fields that need to be constrained in this manner:

struct my_struct {
    a : uint;
    b : uint;
    c : uint;
    d : uint;
    keep 3*a + 4*b + 5*c + 6*d == 206 and a + b + c + d == 50;

    my_method() @clk_event is {
        while (TRUE) {
            if (ctr == 0) {
                gen a;
                gen b;
                gen c;
                gen d;
            };
            if (ctr == 50) {
                ctr = 0;
            } else {
                ctr += 1;
            };
            wait cycle;
        };
    };
};

I basically want to generate a new set of values for a, b, c, and d periodically. The above code is not working as their values did not change in my simulation. Any idea how to do it?

score 2 · Accepted Answer · answered Jan 25 '17 at 09:00

2

When you generate one field, other fields can't change their values, they are inputs for the constraints. Given your constraints, there can be only one correct value for a field if three other can't change.

You probably need to modify the design and put the fields with constraints under a struct, and have a field of this struct type. So instead of four separate gens, you will have only one, and it will do the job right.

answered Jan 25 '17 at 09:00

Rodion Melnikov

338
1
4

This definitely solved the problem. I can now see the struct items getting new set of values every time I generate it. Thank you! – renvill Jan 27 '17 at 03:27

Specman on-the-fly generation for multiple constrained items

1 Answers1