ELEC50010-IAC-CW/rtl/mips_cpu_alu.v

module mips_cpu_alu(
  input signed logic[31:0] A, B,//alu_in1, alu_in2 -The two ALU inputs

  input logic [5:0] ALUFlags, //Output from ALU control - 6bits as there are 48 different instructions in our ISA that we need to implement

    /*  The ALU Flags is 6 bits for now update when reduced */

  output logic ALUZero, //Is the output of the ALU 0? - used to check result

  output logic[31:0] ALUOut, // The ouput of the ALU 
  
  input logic[15:0] immediate, 

  input logic[4:0] shamt

);

  input [15:0] immediate;

  reg [31:0] SignExtend, ZeroExtend;
// Instructions commented out have been accounted for 

    /* Using an enum to define constants */
    //typedef enum logic[5:0] {
        //ADDIU = 6'd0, //Add immediate unsigned (no overflow)
        //ADDU = 6'd1, 	//Add unsigned (no overflow)
       //AND = 6'd2, 	//Bitwise and
        //ANDI = 6'd3, 	//Bitwise and immediate
        //BEQ	 = 6'd4,    //Branch on equal
        //BGEZ = 6'd5, 	//Branch on greater than or equal to zero
        //BGEZAL = 6'd6, 	//Branch on non-negative (>=0) and link
        //BGTZ = 6'd7, 	//Branch on greater than zero
        //BLEZ = 6'd8, 	//Branch on less than or equal to zero
        //BLTZ = 6'd9, 	//Branch on less than zero
        //BLTZAL = 6'd10, //Branch on less than zero and link
        //BNE = 6'd11,    //Branch on not equal
        //DIV = 6'd12, 	//Divide
        //DIVU = 6'd13, 	//Divide unsigned
        J = 6'd14, 	    //Jump
        JALR = 6'd15, 	//Jump and link register
        JAL = 6'd16, 	//Jump and link
        JR = 6'd17, 	//Jump register
        //LB = 6'd18, 	//Load byte
        //LBU = 6'd19,   	//Load byte unsigned
        //LH = 6'd20, 	//Load half-word
        //LHU = 6'd21, 	//Load half-word unsigned
        //LUI = 6'd22, 	//Load upper immediate
        LW = 6'd23, 	//Load word
        LWL = 6'd24, 	//Load word left
        LWR	= 6'd25,    //Load word right
        MTHI = 6'd26, 	//Move to HI
        MTLO = 6'd27, 	//Move to LO
        //MULT = 6'd28, 	//Multiply
        //MULTU = 6'd29, 	//Multiply unsigned
        //OR = 6'd30, 	//Bitwise or
        //ORI	= 6'd31,    //Bitwise or immediate
        //SB = 6'd32, 	//Store byte
        //SH = 6'd33, 	//Store half-word
        //SLL = 6'd34,    //Shift left logical
        //SLLV = 6'd35, 	//Shift left logical variable
        //SLT = 6'd36, 	//Set on less than (signed)
        //SLTI = 6'd37, 	//Set on less than immediate (signed)
        //SLTIU = 6'd38, 	//Set on less than immediate unsigned
        //SLTU = 6'd39, 	//Set on less than unsigned
        //SRA = 6'd40, 	//Shift right arithmetic
       // SRAV = 6'd41, 	//Shift right arithmetic
        //SRL = 6'd42, 	//Shift right logical
        //SRLV = 6'd43, 	//Shift right logical variable
       //SUBU = 6'd44, 	//Subtract unsigned
        //SW = 6'd45, 	//Store word
        //XOR  = 6'd46,   //Bitwise exclusive or
       //XORI = 6'd47, 	//Bitwise exclusive or immediate
    //} ALUFlags;

/* This is how I believe our ctrl flags should be arranged */

  typedef enum logic [6:0]{


  } ALUFlags;

  always @(A,B, ALUFlags)
  begin

  SignExtend = {{16{immediate[15]}}, immediate};
  ZeroExtend = {{16{1'b0}}, immediate};

    case(ALUFlags)
      ADD: begin
          ALUOut = A + B; // is it = or <= ??
      end
      
      SUB: begin
          ALUOut = A - B; 
      end        

      MULT: begin
          ALUOut = A * B; 
      end

      DIV: begin
          ALUOut = A / B;
      end


      XOR: begin
          ALUOut = A^B;
      end

      OR: begin
          ALUOut = A | B;
      end
      
      SLL: begin
          ALUOut = B << shamt //Shamt is instruction read data [10:6]
      end

      SRL: begin
          ALUOut = B >> shamt //Shamt is instruction read data [10:6]
      end        

      SLLV: begin
          ALUOut = B << A
      end

      SRLV: begin
          ALUOut = B >> A
      end     

      AND: begin
          ALUOut = A & B;
      end
      
      BEQ: begin
          if A == B begin
              ALUOut = 0;
          end
          else begin
            ALUOut = ALUOut;
          end
          
      end

      BGEZ: begin
          if A>=0 begin
            ALUOut = 0;
          end
          else begin
            ALUOut = ALUOut;
          end
      end

      BGEZAL: begin
          if A>=0 begin
            ALUOut = 0;
          end
          else begin
            ALUOut = ALUOut;
          end
      end

      BGTZ: begin
          if A>0 begin
            ALUOut = 0;
          end
          else begin
            ALUOut = ALUOut;
          end
      end


      BLEZ: begin
          if A<=0 begin
            ALUOut = 0;
          end
          else begin
            ALUOut = ALUOut;
          end
      end

      BNE: begin
          if A<=0 begin
            ALUOut = 0;
          end
          else begin
            ALUOut = ALUOut;
          end
      end

      LB: begin
        ALUOut = A + SignExtend;
      end

      LBU: begin
        ALUOut = A + ZeroExtend;
      end

      LH: begin
        ALUOut = A + SignExtend;
      end

      LHU: begin
        ALUOut = A + ZeroExtend;
      end

      LUI: begin
          ALUOut = {immediate, {16{1'b0}}};
      end

      SB: begin
        ALUOut = A + SignExtend;
      end

      SH: begin
        ALUOut = A + SignExtend;
      end

      SLT: begin
        ALUOut = $signed(A) < $signed(B) ? 1 : 0;
      end

      SLTU: begin
        ALUOut = A < B ? 1 : 0;
      end

      SRA: begin
        ALUOut = $signed($signed(B) >>> shamt);  
      end

      SRAV: begin
        ALUOut = $signed($signed(B) >>> A);  
      end

      SW: begin
        ALUOut = A + SignExtend;
      end


    endcase
  end
	
  always @(ALUOut) begin
		if (ALUOut == 0) begin
			ALUZero <= 1;
		end else begin
			ALUZero <= 0;
		end
	
	end
	end


endmodule