dff_tb

class random_input ; // Sys temVer i log Clas s f o r cons t rained randomi zat ion
        rand int d ; //random input v a r i a b l e
        constraint c1 {d >= 0 ; d <= 1 ;} // d can only be between 0 and 1 i n c l u s i v e
        rand int reset; // Random r e s e t v a r i a b l e
        constraint c2 {
                reset dist {0:=8 ,1:= 2} ; // r e s e t i s `0 ' 80% of the t ime ; `1 ' 20% of the t ime
        }
endclass

// Sys temVer i log t e s t module f o r b e h a v i o r a l D Fl ip??Flop
module dff_svtm();
reg clk;
reg d;
reg reset;
wire q;
wire q_bar ;
dff_B DUT( clk , reset , d , q , q_bar ) ; // Po s i t i v e edge t r i g g e r e d f l i p ??f l o p
// Sp e c i f y coverage
covergroup myCoverGroup @ (clk); // Check coverage when ever c l k changes
Q: coverpoint q ; // Al l p o s s i b l e v a lue s ( i . e . 0 , 1)
Q BAR: coverpoint q_bar{ // Trans i t ion 0 to 1 and 1 to 0
bins t1 = (0=>1);
bins t2 = (1=>0);
}
RESET: coverpoint reset{ // Value 0 and value 1
bins zero = {0};
bins one = {1};
}
CROSS COVERAGE: cross Q, RESET;
endgroup

initial
begin
random_input rb ; // Declare random input v a r i a b l e
myCoverGroup cg ; // Declare myCoverGroup v a r i a b l e
rb = new() ; // I n s t a n t i a t e random input v a r i a b l e
cg = new() ; // I n s t a n t i a t e myCoverGroup v a r i a b l e
// Do the s tandard t e s t module s e tup
clk <= 1'b1 ;
d <= 1'b0 ;
reset <= 1'b1 ;
#15 reset <= 1'b0 ;
forever
begin
// Create new random input s and apply them
assert ( rb.randomize() )
#20 d <= rb.d ;
reset <= rb.reset ;
end
end
always #10 clk <= ~clk ; // Generate c l o c k s i g n a l
endmodule