module CPU(
	input  reset                        , 
	input  clk                          , 
	output MemRead                      , 
	output MemWrite                     ,
	output [32 -1:0] MemBus_Address     , 
	output [32 -1:0] MemBus_Write_Data  , 
	input  [32 -1:0] Device_Read_Data 
);
	
	// PC register
	reg  [31 :0] PC;
	wire [31 :0] PC_next;
	wire [31 :0] PC_plus_4;

	always @(posedge reset or posedge clk)
		if (reset)
			PC <= 32'h00000000;
		else
			PC <= PC_next;
	
	assign PC_plus_4 = PC + 32'd4;
	
	// Instruction Memory
	wire [31 :0] Instruction;
	InstructionMemory instruction_memory1(
		.Address        (PC             ), 
		.Instruction    (Instruction    )
	);

	// Control 
	wire [2 -1:0] RegDst    ;
	wire [2 -1:0] PCSrc     ;
	wire          Branch    ;
	wire          MemRead   ;
	wire          MemWrite  ;
	wire [2 -1:0] MemtoReg  ;
	wire          ALUSrc1   ;
	wire          ALUSrc2   ;
	wire [4 -1:0] ALUOp     ;
	wire          ExtOp     ;
	wire          LuOp      ;
	wire          RegWrite  ;
	
	Control control1(
		.OpCode     (Instruction[31:26] ), 
		.Funct      (Instruction[5 : 0] ),
		.PCSrc      (PCSrc              ), 
		.Branch     (Branch             ), 
		.RegWrite   (RegWrite           ), 
		.RegDst     (RegDst             ), 
		.MemRead    (MemRead            ),	
		.MemWrite   (MemWrite           ), 
		.MemtoReg   (MemtoReg           ),
		.ALUSrc1    (ALUSrc1            ), 
		.ALUSrc2    (ALUSrc2            ), 
		.ExtOp      (ExtOp              ), 
		.LuOp       (LuOp               ),	
		.ALUOp      (ALUOp              )
	);
	
	// Register File
	wire [32 -1:0] Databus1;
	wire [32 -1:0] Databus2; 
	wire [32 -1:0] Databus3;
	wire [5  -1:0] Write_register;

	assign Write_register = (RegDst == 2'b00)? Instruction[20:16]: (RegDst == 2'b01)? Instruction[15:11]: 5'b11111;

	RegisterFile register_file1(
		.reset          (reset              ), 
		.clk            (clk                ),
		.RegWrite       (RegWrite           ), 
		.Read_register1 (Instruction[25:21] ), 
		.Read_register2 (Instruction[20:16] ), 
		.Write_register (Write_register     ),
		.Write_data     (Databus3           ), 
		.Read_data1     (Databus1           ), 
		.Read_data2     (Databus2           )
	);

	// Extend
	wire [32 -1:0] Ext_out;
	assign Ext_out = { ExtOp? {16{Instruction[15]}}: 16'h0000, Instruction[15:0]};
	
	wire [32 -1:0] LU_out;
	assign LU_out = LuOp? {Instruction[15:0], 16'h0000}: Ext_out;
	
	// ALU Control
	wire [5 -1:0] ALUCtl;
	wire          Sign  ; 

	ALUControl alu_control1(
		.ALUOp  (ALUOp              ), 
		.Funct  (Instruction[5:0]   ), 
		.ALUCtl (ALUCtl             ), 
		.Sign   (Sign               )
	);
		
	// ALU
	wire [32 -1:0] ALU_in1;
	wire [32 -1:0] ALU_in2;
	wire [32 -1:0] ALU_out;
	wire           Zero   ;

	assign ALU_in1 = ALUSrc1? {27'h00000, Instruction[10:6]}: Databus1;
	assign ALU_in2 = ALUSrc2? LU_out: Databus2;

	ALU alu1(
		.in1    (ALU_in1    ), 
		.in2    (ALU_in2    ), 
		.ALUCtl (ALUCtl     ), 
		.Sign   (Sign       ), 
		.out    (ALU_out    ), 
		.zero   (Zero       )
	);
		
	// Data Memory
	wire [32 -1:0] Memory_Read_Data ;
	wire           Memory_Read      ;
	wire           Memory_Write     ;
	wire [32 -1:0] MemBus_Read_Data ;

	DataMemory data_memory1(
		.reset      (reset              ), 
		.clk        (clk                ), 
		.Address    (MemBus_Address     ), 
		.Write_data (MemBus_Write_Data  ), 
		.Read_data  (Memory_Read_Data   ), 
		.MemRead    (Memory_Read        ), 
		.MemWrite   (Memory_Write       )
	);

	
	assign Memory_Read          = MemRead ;
	assign Memory_Write         = MemWrite;
	assign MemBus_Address       = ALU_out ;
	assign MemBus_Write_Data    = Databus2;
	assign MemBus_Read_Data     = Memory_Read_Data;
	
	
	// write back
	assign Databus3 = (MemtoReg == 2'b00)? ALU_out: (MemtoReg == 2'b01)? MemBus_Read_Data: PC_plus_4;
	
	// PC jump and branch
	wire [32 -1:0] Jump_target;
	assign Jump_target = {PC_plus_4[31:28], Instruction[25:0], 2'b00};
	
	wire [32 -1:0] Branch_target;
	assign Branch_target = (Branch & Zero)? PC_plus_4 + {LU_out[29:0], 2'b00}: PC_plus_4;
	
	assign PC_next = (PCSrc == 2'b00)? Branch_target: (PCSrc == 2'b01)? Jump_target: Databus1;

endmodule