由于MIPS各个版本之间的操作数会变，如果出现无法识别的情况
需要根据官方的MIPS instruction手册逐条核对，此处的版本为Rev.1
//******MIPS-55*********//
parameter //SPECIAL OP LIST 5-0
ADDU = 6'b100001,
SUBU = 6'b100011,
ADD = 6'b100000,
SUB = 6'b100010,
AND = 6'b100100,
OR = 6'b100101,
XOR = 6'b100110,
NOR = 6'b100111,
SLT = 6'b101010,
SLTU = 6'b101011,
SRL = 6'b000010,
SRA = 6'b000011,
SLL = 6'b000000,
SLLV = 6'b000100,
SRLV = 6'b000110,
SRAV = 6'b000111,
JR = 6'b001000,
JALR = 6'b001001,
MULT = 6'b011000,
MULTU = 6'b011001,
DIV = 6'b011010,
DIVU = 6'b011011,
MFHI = 6'b010000,
MFLO = 6'b010010,
MTHI = 6'b010001,
MTLO = 6'b010011,
BREAK = 6'b001101,
SYSCALL = 6'b001100,
TEQ = 6'b110100,
//SPECIAL 2 func
CLZ = 6'b100000,
MUL = 6'b000010,
//REGIMM OP LIST 20-16
BLTZ = 5'b00000,
BGEZ = 5'b00001,
//COP0 OP LIST
ERET = 6'b011000, //5-0&&25TH=1
MFC0 = 5'b00000, //20-16
MTC0 = 5'b00100,
//OPCODE FIELD 31-26
ADDI = 6'b001000,
ADDIU = 6'b001001,
ANDI = 6'b001100,
ORI = 6'b001101,
XORI = 6'b001110,
LW = 6'b100011,
SW = 6'b101011,
BEQ = 6'b000100,
BNE = 6'b000101,
BLEZ = 6'b000110,
BGTZ = 6'b000111,
SLTI = 6'b001010,
SLTIU = 6'b001011,
LUI = 6'b001111,
J = 6'b000010,
JAL = 6'b000011,
LB = 6'b100000,// Load Byte Function=6'h24
LBU = 6'b100100,// 1Load Byte Unsigned
LH = 6'b100001,// Load high
LHU = 6'b100101,// Load High Unsigned
SB = 6'b101000,// Send Byte
SH = 6'b101001,// Send High
SPECIAL = 6'b000000,
SPECIAL2= 6'b011100,
REGIMM = 6'b000001,
COP0 = 6'b010000;
//ALU OPCODE
parameter _ADDU = 4'b0000; //r=a+b unsigned
parameter _ADD = 4'b0010; //r=a+b signed
parameter _SUBU = 4'b0001; //r=a-b unsigned
parameter _SUB = 4'b0011; //r=a-b signed
parameter _AND = 4'b0100; //r=a&b
parameter _OR = 4'b0101; //r=a|b
parameter _XOR = 4'b0110; //r=a^b
parameter _NOR = 4'b0111; //r=~(a|b)
parameter _LUI = 4'b1000; //r={b[15:0],16'b0}
parameter _SLT = 4'b1011; //r=(a-b<0)?1:0 signed
parameter _SLTU = 4'b1010; //r=(a-b<0)?1:0 unsigned
parameter _SRA = 4'b1100; //r=b>>>a
parameter _SLL = 4'b1110; //r=b<<a
parameter _SRL = 4'b1101; //r=b>>a
parameter _SYSCALL = 4'b1000,
_BREAK = 4'b1001,
_TEQ = 4'b1101;
wire [5:0] op = instr[31:26];
assign rs = instr[25:21];
assign rt = instr[20:16];
assign rd = instr[15:11];
wire [5:0] func = instr[5:0];
wire [4:0] shamt = instr[10:6];
wire [15:0] imm = instr[15:0];
wire [25:0] addr = instr[25:0];
parameter SIGN = 1'b1;
parameter UNSIGN = 1'b0;
wire imm_sign = (op==ANDI||op==ORI||op==XORI)?UNSIGN:SIGN;
wire [31:0] shamt_ext = {27'b0,shamt};
wire [31:0] imm_ext = imm_sign?{{(16){imm[15]}},imm}:{16'b0,imm};
reg [31:0] load_data,clz_data;
assign waddr = (op==SPECIAL||op==SPECIAL2)? rd: (op==JAL) ?5'b11111:rt;