RE: [sv-ec] rand_mode applied to a dynamic array

Ray,

Here's my take on your questions:

Assume that there is such a thing as an array's rand_mode. The rand_mode
of a particular array element is the AND of the rand_mode of the element
and the rand_mode of the array. I believe this clarifies your questions.

1) Applying rand_mode(0) to the entire array should do two things: a)
set the rand_mode of each element of the array to inactive, and b) set
to inactive the rand_mode of the array size (for resizable arrays). I
thought we had written that in the LRM, but can't remember where it is.
This means that calling rand_mode on a re-sizeable array is different
from calling rand_mode on each array element.

2) There is no semantic difference if the order of the two statements is
reversed, that is, the rand_mode of the array continues to be inactive,
and hence, the rand_mode of each array element is inactive. In your
particular example, constraint c1 will be violated and randomize will
fail and trigger the assertion.

Given this definition, one could arguably implement the function version
of h1.x.rand_mode as returning the array's rand_mode. But, I realize
that this is not well defined at the moment.

	Arturo

-----Original Message-----
From: owner-sv-ec@eda.org [mailto:owner-sv-ec@eda.org] On Behalf Of
Ryan, Ray
Sent: Tuesday, September 02, 2008 3:39 PM
To: sv-ec@eda.org
Subject: [sv-ec] rand_mode applied to a dynamic array


We have had some questions about the behavior of the rand_mode method
for a dynamic array. Consider the following example:

module top;

  class my_class;
    rand int x[];

    constraint c1 { x.size() == 5; }
  endclass

  my_class h1 = new();

  initial begin
    h1.x = new[3];

    h1.x.rand_mode(0);
    assert( h1.randomize() );
    $display(h1.x[0].rand_mode(),
h1.x[1].rand_mode(),h1.x[2].rand_mode(),h1.x[3].rand_mode(),h1.x[4].rand
_mode() );
    $display( h1.x );

  end
endmodule


Questions:
1) Does the call to h1.x.rand_mode(0) effect whether the dynamic array
h1.x is resized in the subsequent call to h1.randomize() ?
2) If the order of first two statements of the initial block are
reversed which elements of the dynamic array are considered 'active' in
the
subsequent randomize call ?   IE, if the initial block was:
  initial begin
	h.x.rand_mode(0);
	h.x = new[3];
	assert (h1.randomize() );
  end

-----------------

I'd expect:
1) h1.x.rand_mode(0) sets each element to 'inactive'. In the subsequent
randomize
the array will be resize to 5 elements. The first 3 will be inactive,
the last
two will be active.
2) With the statements reversed: in the call to h.x.rand_mode(0), there
are no elements so this statement does nothing. When the array is
resized, the
rand_mode status of the new elements is 'active'.


- Ray Ryan


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