WWW.TESTBENCH.IN - Systemverilog Randomization

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Specman E
Interview Questions

STATIC CONSTRAINT

If a constraint block is declared as static, then constraint mode on that block will effect on all the instancess of that class. In the following example, two objects obj_1 and obj_2 are declared. Constraints Var1_c is static and Var2_c is not static. When constraint_mode is used to switch off the constraints in in obj_2, constraint var1_c in obj_1 is also switched off.

EXAMPLE:
class A;
rand integer Var1, Var2;
static constraint Var1_c { Var1 == 10 ;}
constraint Var2_c { Var2 == 10 ;}
endclass

program A_p_46;
A obj_1 = new;
A obj_2 = new;
initial
begin
obj_2.Var1_c.constraint_mode(0);
obj_2.Var2_c.constraint_mode(0);
repeat(10)
begin
void'(obj_1.randomize());
$display("obj_1.Var1 : %d ,obj_1.Var2 : %d ",obj_1.Var1,obj_1.Var2);
end
end
endprogram

RESULTS:

# obj_1.Var1 : 733126180 ,obj_1.Var2 : 10
# obj_1.Var1 : -119008195 ,obj_1.Var2 : 10
# obj_1.Var1 : 342785185 ,obj_1.Var2 : 10
# obj_1.Var1 : 679818185 ,obj_1.Var2 : 10
# obj_1.Var1 : -717162992 ,obj_1.Var2 : 10
# obj_1.Var1 : 664520634 ,obj_1.Var2 : 10
# obj_1.Var1 : -1944980214 ,obj_1.Var2 : 10
# obj_1.Var1 : -1350759145 ,obj_1.Var2 : 10
# obj_1.Var1 : -1374963034 ,obj_1.Var2 : 10
# obj_1.Var1 : -462078992 ,obj_1.Var2 : 10

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