Constraint array

[rabh]

Hi,
I would like to know the difference between the two lines in the constraint statement below:

class array ;
	parameter size = 10;
	parameter int UNIQ = 3;
	rand bit [5:0] array [size];
	rand bit [5:0] rand_element;

	constraint AB {
		array.sum () with (int'(item == rand_element)) == UNIQ;
	//	array.sum () with ((item == rand_element)) == UNIQ;
	}
endclass

The one which is commented out gives constraint errors, the other works fine. The constraint is to have 3 same elements in an array of size 10.

[dave_59]

Constraints to generate random password in SV

In reply to Liiiiiz: The result of the expression item inside {[97:122]} is true 1’b1 or false 1’b0, both 1-bit. The sum() of those expressions will also be a 1-bit result. You just need to cast that expression to a large enough width so the sum of 10 possible 1’b1 values does not overflow. Cast to 4-bits or int would work as well. I think Alokpati used 7 because that was the element size of pw array, but that size is no longer relevant. Only 10 numbers can be chosen because that is the size…

[Mmathur]

Hi, as Dave mentioned the expression will give a 1 bit value, which then needs to cast to int or larger width for the sum constraint to work.