Control Unit and ALU Control Op

[er693310]

Hello everyone. I'm designing a control unit for a simple 32 bit mips CPU. For some reason, when I give the Control unit a subtract instruction, it will treat it as an add (ALUControl for sub is 110 and ALUControl from add is 010).

I've attached my code here, could someone tell me what's wrong? I've monitored all the bits coming into ALUControl[2] (i.e., funct[1], ALUOp[1], and ALUOp[0]) and they've been 1, 1, and 0 respectively. Thus, I should get 110 from my ALUControl! Please help me!

`timescale 1ns / 1ps
//////////////////////////////////////////////////////////////////////////////////
// Control Unit Module
//////////////////////////////////////////////////////////////////////////////////
module Control(opcode, funct, ALUSrc, ALUOp, RegDst, MemWrite, MemRead, Beq, Bne, Jump, MemToReg, RegWrite, ALUControl, Control);

input [5:0] opcode;
input [5:0] funct;

output ALUSrc, RegDst, MemWrite, MemRead, Beq, Bne, Jump, MemToReg, RegWrite;
output [1:0] ALUOp;
output [2:0] ALUControl;
output [8:0] Control;


reg ALUSrc, RegDst, MemWrite, MemRead, Beq, Bne, Jump, MemToReg, RegWrite, Branch;
reg [1:0] ALUOp;
reg [2:0] ALUControl;
reg RFormat, lw, sw, beq, bne, jmp;
reg [8:0] Control;
reg [3:0] EX;
reg [2:0] M;
reg [1:0] WB;

always@(opcode)
begin
assign RFormat = (~opcode[5] & ~opcode[4] & ~opcode[3] & ~opcode[2] & ~opcode[1] & ~opcode[0]);
assign lw = (opcode[5] & ~opcode[4] & ~opcode[3] & ~opcode[2] & opcode[1] & opcode[0]);
assign sw = (opcode[5] & ~opcode[4] & opcode[3] & ~opcode[2] & opcode[1] & opcode[0]);
assign beq = (~opcode[5] & ~opcode[4] & ~opcode[3] & opcode[2] & ~opcode[1] & ~opcode[0]);
assign bne = (~opcode[5] & ~opcode[4] & ~opcode[3] & opcode[2] & ~opcode[1] & opcode[0]);
assign jmp = (~opcode[5] & ~opcode[4] & ~opcode[3] & ~opcode[2] & opcode[1] & ~opcode[0]);

assign RegDst = RFormat;
assign ALUSrc = (lw | sw);
assign MemToReg = lw;
assign RegWrite = (RFormat | lw);
assign MemRead = lw;
assign MemWrite = sw;
assign Beq = beq;
assign Bne = bne;
assign Jump = jmp;
assign Branch = beq | bne;

ALUOp[1] = (RFormat | jmp);
ALUOp[0] = (bne | beq | jmp);

// Execution control
EX[3] = RegDst;
EX[2] = ALUSrc;
EX[1] = RFormat;
EX[0] = Beq;

// Memory control
M[2] = Branch;
M[1] = MemRead;
M[0] = MemWrite;

// Write-back control
WB[1] = MemToReg;
WB[0] = RegWrite;

// Final control
Control[8:7] = WB;
Control[6:4] = M;
Control[3:0] = EX;

ALUControl[0] = (funct[0] | funct[3]) & ALUOp[1];
ALUControl[1] = (~funct[2] | ~ALUOp[1]);

ALUControl[2] = funct[1] & ALUOp[1] | ALUOp[0];

end



endmodule