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`timescale 1ns / 1ps

//////////////////////////////////////////////////////////////////////////////////

// Company: 

// Engineer: 

// 

// Create Date:    18:33:46 12/29/2016 

// Design Name: 

// Module Name:    ALU_Ctr 

// Project Name: 

// Target Devices: 

// Tool versions: 

// Description: 

//

// Dependencies: 

//

// Revision: 

// Revision 0.01 - File Created

// Additional Comments: 

//

//////////////////////////////////////////////////////////////////////////////////

`include "macros.v"

module ALU_Ctr(

input wire [5:0] opcode,

input wire [5:0] funct,

input wire [1:0] ALUOp,

output wire [3:0] cmd

    );

        /* the ALU command */

        assign cmd = OUT( funct, ALUOp);

         /* the first-level decode */

         function [3:0]  OUT;

                input [5:0] funct;

                input [1:0] ALUOp;

                case( ALUOp )

                2'b00: OUT = `ALU_ADD;

                2'b01: OUT = `ALU_SUB;

                2'b10: OUT = DECODE( funct );

                2'b11: OUT = DECODE2( opcode );

                default: OUT = 4'bxxxx;

                endcase

         endfunction

         /* the second-level decode */

         function [3:0] DECODE;

                input [5:0] funct;

                case( funct )

                `R_OP_AND:      DECODE = `ALU_AND;

                `R_OP_OR:       DECODE = `ALU_OR;

                `R_OP_ADD:      DECODE = `ALU_ADD;

                `R_OP_SUB:      DECODE = `ALU_SUB;

                `R_OP_SLT:      DECODE = `ALU_SLT;

                `R_OP_NOR:      DECODE = `ALU_NOR;

                `R_OP_SLLV:     DECODE = `ALU_SLLV;

                `R_OP_SRLV:     DECODE = `ALU_SRLV;

                default: DECODE = 4'bxxxx;

                endcase

         endfunction

         /* the third-level decode */

         function [3:0] DECODE2;

                input [5:0] opcode;

                begin

                        case( opcode )

                        `OPCODE_I_ADDI: DECODE2 = `ALU_ADD;

                        `OPCODE_I_ANDI: DECODE2 = `ALU_AND;

                        `OPCODE_I_ORI:   DECODE2 = `ALU_OR;

                        `OPCODE_I_XORI: DECODE2 = `ALU_XOR;

                        `OPCODE_I_LUI:   DECODE2 = `ALU_LU;

                        default:                         DECODE2 = 4'bxxxx;

                        endcase

                end

         endfunction

endmodule