Re: [sv-ec] Specifying rand_mode for packed array elements

Ray,
 That paragraph refers to unpacked arrays. For packed arrays the part
 selection is not allowed with rand_mode method, i.e, one can not turn
 off randomization for individual bit. It works on elements of unpacked
 arrays.
 I have changed your example slightly and show a sample result from Vera
 simulation, in your example wheel is unpacked array of 8bits.
 For individual bit manipulation after the declaration of class one
 can use the in-line constraints- with() upon randomize call.
Regards,
- Mehdi

-----------------------------------
  class Spin;
    rand [7:0] bit wheel[0:7];
    rand [7:0] x;
    constraint c { x < 50; }
    constraint c2 { foreach ( wheel[i] inside {0:100};}
    // ... other declarations
   endclass
 
   int j;
   Spin big = new;
   big.wheel.rand_mode(1); // enable randomization of all bits
   for (i=0; i<8; i++)
   begin
     big.wheel[i].rand_mode(0); // disable randomization of another bit
     big.randomize();
     ... other test code
   end

Sample result:
 -- All eight randomized on --
----------------- 0 1 2 3 4 5 6 7
------------------------------------------------------
 [eight wheeler] 2, 34, 74, 19, 0, 72, 95, 83,
 -- rand_mode off one wheel at a time, from 0 to 7 --
----------------- 0 1 2 3 4 5 6 7
------------------------------------------------------
 [eight wheeler] 2, 19, 0, 51, 10, 35, 47, 89,
 [eight wheeler] 2, 19, 13, 61, 79, 95, 6, 22,
 [eight wheeler] 2, 19, 13, 45, 46, 18, 17, 58,
 [eight wheeler] 2, 19, 13, 45, 57, 23, 67, 55,
 [eight wheeler] 2, 19, 13, 45, 57, 10, 73, 69,
 [eight wheeler] 2, 19, 13, 45, 57, 10, 96, 49,
 [eight wheeler] 2, 19, 13, 45, 57, 10, 96, 51,
 [eight wheeler] 2, 19, 13, 45, 57, 10, 96, 51,
--------------------------------------------------------

> X-UIDL: b01c87cb662ddc632fc7430e2a102935
> To: sv-ec@eda.org
> Subject: [sv-ec] Specifying rand_mode for packed array elements
> Date: Mon, 5 Apr 2004 16:51:34 -0700
> X-Scan-Signature: 5f5707d583650bc631c837957f10fbee
> X-pstn-levels: (S:29.04579/99.33400 R:95.9108 P:95.9108 M:98.0742 C:79.5348 )
>
> Section 12.7 the first paragraph after Table 12-1 states:
>
> "For array variables, random_variable can specify individual elements using
> the corresponding index. Omitting
> the index results in all the elements of the array being affected by the
> call."
>
> As stated, I believe this allows disabling of randomization for the
> individual bits
> of a packed random variable. Is this the intended semantics?
>
> For example, is the following legal?
>
> class Spin;
> rand [7:0] bit wheel, x;
> constraint c { x < wheel; };
> ... other declarations
> endclass
>
> int i;
> Spin big = new;
> big.wheel.rand_mode(1); // enable randomization of all bits
> for (i=7; i+0; i=i-1)
> begin
> big.wheel[i].rand_mode(0); // disable randomization of another bit
> big.randomize();
> ... other test code
> end
>
>
> -- Ray
Received on Tue Apr 6 17:40:51 2004