WWW.TESTBENCH.IN - Systemverilog Randomization

Tutorials

Specman E
Interview Questions

INLINE CONSTRAINT

Inline constraints allows to add extra constraints to already existing constraints which are declared inside class. If you have constraints already defined for variavle var, solver solves those constraints along with the in-line constraints.

EXAMPLE:
class inline;
rand integer Var;
constraint default_c { Var > 0 ; Var < 100;}
endclass

program inline_p_35;
inline obj;
initial
begin
obj = new();
repeat(5)
if(obj.randomize() with { Var == 50;})
$display(" Randodmize sucessful Var %d ",obj.Var);
else
$display(" Randomization failes");
end
endprogram

RESULTS:

# Randodmize sucessful Var 50
# Randodmize sucessful Var 50
# Randodmize sucessful Var 50
# Randodmize sucessful Var 50
# Randodmize sucessful Var 50

In the above example, by default only default_c constraints are considered. Using inline constraint Var == 50 resulted value on variable Var based on both the default_c and inline constraints.

The scope for variable names in a constraint block, from inner to outer, is randomize()...with object class, automatic and local variables, task and function arguments, class variables, and variables in the enclosing scope. The randomize()...with class is brought into scope at the innermost nesting level. In the f.randomize() with constraint block, x is a member of class Foo and hides the x in program Bar. It also hides the x argument in the doit() task. y is a member of Bar. z is a local argument.

In the example below, the randomize()...with class is Foo.

EXAMPLE:
class Foo;
rand integer x;
endclass

program Bar_36;
Foo obj = new();
integer x;
integer y;

task doit(Foo f, integer x, integer z);
int result;
result = f.randomize() with {x < y + z;};
$display(":: obj.x : %d :: x : %d :: y : %d :: z : %d ::",obj.x,x,y,z);
endtask

initial
begin
x = 'd10;

repeat(5)
begin
y = $urandom % 10;
doit(obj,x ,'d12);
end
end
endprogram

RESULTS:

:: obj.x : -1538701546 :: x : 10 :: y : 5 :: z : 12 ::
:: obj.x : -1048494686 :: x : 10 :: y : 9 :: z : 12 ::
:: obj.x : -1122673684 :: x : 10 :: y : 8 :: z : 12 ::
:: obj.x : -2050360121 :: x : 10 :: y : 7 :: z : 12 ::
:: obj.x : -886228933 :: x : 10 :: y : 3 :: z : 12 ::

By seeing this output we can tell the variable which used in inline constraint is class member x.

constraint { x < y + z } means { obj.x < Bar_36.y + do_it.z }

<< PREVIOUS PAGE

TOP

NEXT PAGE >>