decoder.v

MIPS CPU tested in Icarus Verilog

// Operations: ADD, ADDU, SUB, SUBU, AND, OR, NOR, XOR, SLL, SRA, SRL

module decoder(Clock, Reset, Instruction, Branch, Jump, Write_RF, Src2, ALUOP, RegDest, Memory_Read, Memory_Write, Mem2Reg, IntFP, ArSh);

   parameter InstWidth = 32;

   // ---------------------------- Input ports ----------------------------
   input Clock;
   input Reset;
   input [InstWidth-1:0] Instruction;

   // ---------------------------- Output ports ----------------------------
   output 		 Branch;
   output 		 Jump;
   output 		 Write_RF;
   output 		 Src2;
   output 		 ALUOP;
   output 		 RegDest;
   output 		 Memory_Read;
   output 		 Memory_Write;
   output 		 Mem2Reg;
   output 		 IntFP;
   output 		 ArSh;

   // ---------------------------- Type of Output ports ----------------------------
   reg 			 Branch;
   reg 			 Jump;
   reg 			 Write_RF;
   reg 			 Src2;
   reg [5:0] 		 ALUOP;
   reg [1:0] 		 RegDest;
   reg 			 Memory_Read;
   reg 			 Memory_Write;
   reg [2:0] 		 Mem2Reg;
   reg 			 IntFP;
   reg 			 ArSh;

   // ----------------------------------------------------
   //                  Code Starts Here
   // ----------------------------------------------------

   // Include the definition of all the ALU Operations

   `include "Operations.v"   // File "Operations.v" contains all operation codes
   `include "OperationsFP.v" // File "OperationsFP.v" contains floating point opcodes

   always @ (posedge Clock)
     begin
	if(Reset == 1)
	  begin
	     //If the reset is on, it will clear each output
	     Branch = 1'b0; //With 0, the PC is incremented in 1
	     Jump = 1'b0; //So that PC gets incremented in 1
	     Write_RF = 1'b0; //With 0 we don't write to the register file
	     Src2 = 1'b0; // With 0 the Mux selects Output B from RegFile 
	     ALUOP = NOP; //No Operation Opcode
	     RegDest = 2'b00; // Doesn't matter
	     Memory_Read = 1'b0; //Doesn't read from memory
	     Memory_Write = 1'b0; //Doesn't write to memory
	     Mem2Reg = 3'b000; //With 0 the Mux selects the output from the ALU
	     IntFP = 1'b0; //Select the ALU unit
	     ArSh = 1'b0; //SrcA = I[25-21]
	  end // if (Reset == 1)
	else
	  begin
	     case(Instruction[InstWidth-1:InstWidth-6])
	       NOP: begin
		  Branch = 1'b0; //With 0, the PC is incremented in 1
		  Jump = 1'b0; //So that PC gets incremented in 1
		  Write_RF = 1'b0; //With 0 we don't write to the register file
		  Src2 = 1'b0; // With 0 the Mux selects Output B from RegFile
		  ALUOP = NOP; //No Operation Opcode
		  RegDest = 2'b00; // Doesn't matter
		  Memory_Read = 1'b0; //Doesn't read from memory
		  Memory_Write = 1'b0; //Doesn't write to memory
		  Mem2Reg = 3'b000; //With 0 the Mux selects the output from the ALU
		  IntFP = 1'b0; //Select the ALU unit
		  ArSh = 1'b0; //SrcA = I[25-21]
	       end // case: NOP
	       
	       // ################ Arithmetic Immediate Operations ################
	       ADDI: begin
		  Branch = 1'b0; //With 0, the PC is incremented in 1
		  Jump = 1'b0; //So that PC gets incremented in 1
		  Write_RF = 1'b1; //With 1 we write to the register file
		  Src2 = 1'b1; // With 1 the Mux selects the Immediate Value
		  ALUOP = S_ADD; //ADDI = S_ADD Opcode
		  RegDest = 2'b00; // With 0, the Mux selects Rt
		  Memory_Read = 1'b0; //Doesn't read from memory
		  Memory_Write = 1'b0; //Doesn't write to memory
		  Mem2Reg = 3'b000; //With 0 the Mux selects the output from the ALU
		  IntFP = 1'b0; //Select the ALU unit
		  ArSh = 1'b0; //SrcA = I[25-21]
	       end // case: ADDI

	       ADDIU: begin
		  Branch = 1'b0; //With 0, the PC is incremented in 1
		  Jump = 1'b0; //So that PC gets incremented in 1
		  Write_RF = 1'b1; //With 1 we write to the register file
		  Src2 = 1'b1; // With 1 the Mux selects the Immediate Value
		  ALUOP = S_ADDU; //ADDIU Opcode
		  RegDest = 2'b00; // With 0, the Mux selects Rt
		  Memory_Read = 1'b0; //Doesn't read from memory
		  Memory_Write = 1'b0; //Doesn't write to memory
		  Mem2Reg = 3'b000; //With 0 the Mux selects the output from the ALU
		  IntFP = 1'b0; //Select the ALU unit
		  ArSh = 1'b0; //SrcA = I[25-21]
	       end // case: ADDIU

	       ANDI: begin
		  Branch = 1'b0; //With 0, the PC is incremented in 1
		  Jump = 1'b0; //So that PC gets incremented in 1
		  Write_RF = 1'b1; //With 1 we write to the register file
		  Src2 = 1'b1; // With 1 the Mux selects the Immediate Value
		  ALUOP = S_AND; //ANDI Opcode
		  RegDest = 2'b00; // With 0, the Mux selects Rt
		  Memory_Read = 1'b0; //Doesn't read from memory
		  Memory_Write = 1'b0; //Doesn't write to memory
		  Mem2Reg = 3'b000; //With 0 the Mux selects the output from the ALU
		  IntFP = 1'b0; //Select the ALU unit
		  ArSh = 1'b0; //SrcA = I[25-21]
	       end // case: ANDI

	       ORI: begin
		  Branch = 1'b0; //With 0, the PC is incremented in 1
		  Jump = 1'b0; //So that PC gets incremented in 1
		  Write_RF = 1'b1; //With 1 we write to the register file
		  Src2 = 1'b1; // With 1 the Mux selects the Immediate Value
		  ALUOP = S_OR; //ORI Opcode
		  RegDest = 2'b00; // With 0, the Mux selects Rt
		  Memory_Read = 1'b0; //Doesn't read from memory
		  Memory_Write = 1'b0; //Doesn't write to memory
		  Mem2Reg = 3'b000; //With 0 the Mux selects the output from the ALU
		  IntFP = 1'b0; //Select the ALU unit
		  ArSh = 1'b0; //SrcA = I[25-21]
	       end // case: ORI

	       XORI: begin
		  Branch = 1'b0; //With 0, the PC is incremented in 1
		  Jump = 1'b0; //So that PC gets incremented in 1
		  Write_RF = 1'b1; //With 1 we write to the register file
		  Src2 = 1'b1; // With 1 the Mux selects the Immediate Value
		  ALUOP = S_XOR; //XORI Opcode
		  RegDest = 2'b00; // With 0, the Mux selects Rt
		  Memory_Read = 1'b0; //Doesn't read from memory
		  Memory_Write = 1'b0; //Doesn't write to memory
		  Mem2Reg = 3'b000; //With 0 the Mux selects the output from the ALU
		  IntFP = 1'b0; //Select the ALU unit
		  ArSh = 1'b0; //SrcA = I[25-21]
	       end // case: XORI

	       // ################ Load Operations ################
	       LB: begin
		  Branch = 1'b0; //With 0, the PC is incremented in 1
		  Jump = 1'b0; //So that PC gets incremented in 1
		  Write_RF = 1'b1; //With 1 we write to the register file
		  Src2 = 1'b1; // With 1 the Mux selects the Immediate Value
		  ALUOP = S_ADD; //LB Opcode (ALU Output = Immediate Num extended to 32)
		  RegDest = 2'b00; // With 0, the Mux selects Rt
		  Memory_Read = 1'b1; //Reads from memory
		  Memory_Write = 1'b0; //Doesn't write to memory
		  Mem2Reg = 3'b001; //With 1 the Mux selects the output from the memory after this gets sign extended (24 bits)
		  IntFP = 1'b0; //Select the ALU unit
		  ArSh = 1'b0; //SrcA = I[25-21]
	       end // case: LB

	       LBU: begin
		  Branch = 1'b0; //With 0, the PC is incremented in 1
		  Jump = 1'b0; //So that PC gets incremented in 1
		  Write_RF = 1'b1; //With 1 we write to the register file
		  Src2 = 1'b1; // With 1 the Mux selects the Immediate Value
		  ALUOP = S_ADD; //LBU Opcode (ALU Output = Immediate Num extended to 32)
		  RegDest = 2'b00; // With 0, the Mux selects Rt
		  Memory_Read = 1'b1; //Reads from memory
		  Memory_Write = 1'b0; //Doesn't write to memory
		  Mem2Reg = 3'b010; //With 2 the Mux selects the output from the memory after this gets zero extended (24 bits)
		  IntFP = 1'b0; //Select the ALU unit
		  ArSh = 1'b0; //SrcA = I[25-21]
	       end // case: LBU

	       LH: begin
		  Branch = 1'b0; //With 0, the PC is incremented in 1
		  Jump = 1'b0; //So that PC gets incremented in 1
		  Write_RF = 1'b1; //With 1 we write to the register file
		  Src2 = 1'b1; // With 1 the Mux selects the Immediate Value
		  ALUOP = S_ADD; //LH Opcode (ALU Output = Immediate Num extended to 32)
		  RegDest = 2'b00; // With 0, the Mux selects Rt
		  Memory_Read = 1'b1; //Reads from memory
		  Memory_Write = 1'b0; //Doesn't write to memory
		  Mem2Reg = 3'b011; //With 3 the Mux selects the output from the memory after this gets sign extended (16 bits)
		  IntFP = 1'b0; //Select the ALU unit
		  ArSh = 1'b0; //SrcA = I[25-21]
	       end // case: LH

	       LHU: begin
		  Branch = 1'b0; //With 0, the PC is incremented in 1
		  Jump = 1'b0; //So that PC gets incremented in 1
		  Write_RF = 1'b1; //With 1 we write to the register file
		  Src2 = 1'b1; // With 1 the Mux selects the Immediate Value
		  ALUOP = S_ADD; //LHU Opcode (ALU Output = Immediate Num extended to 32)
		  RegDest = 2'b00; // With 0, the Mux selects Rt
		  Memory_Read = 1'b1; //Reads from memory
		  Memory_Write = 1'b0; //Doesn't write to memory
		  Mem2Reg = 3'b100; //With 4 the Mux selects the output from the memory after this gets zero extended (16 bits)
		  IntFP = 1'b0; //Select the ALU unit
		  ArSh = 1'b0; //SrcA = I[25-21]
	       end // case: LHU

	       LUI: begin
		  Branch = 1'b0; //With 0, the PC is incremented in 1
		  Jump = 1'b0; //So that PC gets incremented in 1
		  Write_RF = 1'b1; //With 1 we write to the register file
		  Src2 = 1'b1; // With 1 the Mux selects the Immediate Value
		  ALUOP = S_ADD;
		  RegDest = 2'b00; // With 0, the Mux selects Rt
		  Memory_Read = 1'b0; //Doesn't read from memory
		  Memory_Write = 1'b0; //Doesn't write to memory
		  Mem2Reg = 3'b100; //With 4 the Mux selects the output from the memory after it gets zero extended
		  IntFP = 1'b0; //Select the ALU unit
		  ArSh = 1'b0; //SrcA = I[25-21]
	       end // case: LUI

	       LW: begin
		  Branch = 1'b0; //With 0, the PC is incremented in 1
		  Jump = 1'b0; //So that PC gets incremented in 1
		  Write_RF = 1'b1; //With 1 we write to the register file
		  Src2 = 1'b1; // With 1 the Mux selects the Immediate Value
		  ALUOP = S_ADD; //LBU Opcode (ALU Output = Immediate Num extended to 32)