//?????
//------------------------------------------------------------------------------
module alu (alu_out, zero, data, accum, alu_clk, opcode);
output [7:0]alu_out;
output zero;
input [7:0] data, accum;
input [2:0] opcode;
input alu_clk;
reg [7:0] alu_out;

parameter 	HLT  =3'b000,
SKZ  =3'b001,
ADD  =3'b010,
ANDD =3'b011,
XORR =3'b100,
LDA  =3'b101,
STO  =3'b110,
JMP  =3'b111;

assign zero = !accum;
always @(posedge  alu_clk)
begin  //?????????????opc_iaddr<15..0>??3?
casex (opcode)	
HLT: alu_out<=accum;
SKZ: alu_out<=accum;
ADD: alu_out<=data+accum;
ANDD: alu_out<=data&accum;
XORR: alu_out<=data^accum;
LDA: alu_out<=data;
STO: alu_out<=accum;
JMP: alu_out<=accum;
default: alu_out<=8'bxxxx_xxxx;
endcase
end
endmodule
//----------------------------------------------------------------------------