/***************************************************
/ Shift Register module by Submodule
/ Programing by seongki
***************************************************/
module Shift_Register_4_str(output [3:0] A_par,input [3:0] I_par,input s1,s0,MSB_in,LSB_in,CLK,Clear);
wire [1:0] select;
assign select = {s1,s0};
stage ST0(I_par[0],I_par[1],LSB_in,I_par[0],A_par[0],select,CLK,Clear);
stage ST1(I_par[1],I_par[2],I_par[0],I_par[1],A_par[1],select,CLK,Clear);
stage ST2(I_par[2],I_par[3],I_par[1],I_par[2],A_par[2],select,CLK,Clear);
stage ST3(I_par[3],MSB_in,I_par[2],I_par[3],A_par[3],select,CLK,Clear);
endmodule
module stage(i0,i1,i2,i3,Q,select,CLK,Clr);
input i0,i1,i2,i3, CLK,Clr;
output Q;
input [1:0] select;
wire mux_out;
Mux_4x_1 M0(mux_out,i0,i1,i2,i3,select);
D_flip_flop M1(Q,mux_out,CLK,Clr);
endmodule
module Mux_4x_1(mux_out,i0,i1,i2,i3,select);
output mux_out;
input i0,i1,i2,i3;
input [1:0] select;
reg mux_out;
always@(select,i0,i1,i2,i3)
case(select)
2'b00:mux_out=i0;
2'b01:mux_out=i1;
2'b10:mux_out=i2;
2'b11:mux_out=i3;
endcase
endmodule
module D_flip_flop(Q,D,CLK,Clr);
output Q;
input D,CLK,Clr;
reg Q;
always@(posedge CLK, negedge Clr)
if(~Clr) Q<=0;
else Q<=D;
endmodule
//testbench
`timescale 1ns/1ns
module tb_Shift_Register_Structural_model;
reg [3:0] I_par;
reg s1,s0,MSB_in,LSB_in,CLK,Clear;
wire [3:0] A_par;
Shift_Register_4_str test1(A_par,I_par,s1,s0,MSB_in,LSB_in,CLK,Clear);
initial
begin
I_par=4'b1111;
Clear=0; MSB_in=0; LSB_in=0; CLK=0; s1=0; s0=0;
#10 CLK=0;
#10 CLK=1;
#10 CLK=0;
#10 CLK=1;
#10 CLK=0;
#10 CLK=1;
#10 Clear=1; MSB_in=0; LSB_in=0; CLK=0; s1=0; s0=0;
#10 CLK=0;
#10 CLK=1;
#10 CLK=0;
#10 CLK=1;
#10 CLK=0;
#10 CLK=1;
#10 Clear=1; MSB_in=0; LSB_in=0; CLK=0; s1=0; s0=1;
#10 CLK=0;
#10 CLK=1;
#10 CLK=0;
#10 CLK=1;
#10 CLK=0;
#10 CLK=1;
#10 Clear=1; MSB_in=0; LSB_in=0; CLK=0; s1=1; s0=0;
#10 CLK=0;
#10 CLK=1;
#10 CLK=0;
#10 CLK=1;
#10 CLK=0;
#10 CLK=1;
#10 Clear=1; MSB_in=0; LSB_in=0; CLK=0; s1=1; s0=1;
#10 CLK=0;
#10 CLK=1;
#10 CLK=0;
#10 CLK=1;
#10 CLK=0;
#10 CLK=1;
#10 CLK=0;
end
endmodule