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//////////////////////////////////////////////////////////////////////

////                                                              ////

//// Copyright (C) 2014-2015 Azmath Moosa                         ////

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//// This source file may be used and distributed without         ////

//// restriction provided that this copyright statement is not    ////

//// removed from the file and that any derivative work contains  ////

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//// This source file is free software; you can redistribute it   ////

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//////////////////////////////////////////////////////////////////////

`timescale 1ns / 1ps

`include "Configuration.v"

module EX_Stage(

        input Clk,

        input RST,

        inout [0:3] stkFlag,

        input ret,

        input [0:`ID_EX_reg_w] ID_EX_reg,

        output [0:`EX_MEM_reg_w] EX_MEM_reg,

        input [0:`dpw] b_EX_MEM_reg, b_MEM_WB_reg

        );

        reg [0:`dpw] bb_MEM_WB_reg;

        wire [0:`type_msb] Type;

        wire [0:`wb_dst_msb] WB_Dest;

        wire [0:`bc_msb] Rd_BC;

        wire [0:`operation_msb] Operation;

        wire [0:`mod_sel_msb] Module;

        wire [0:`dpw] OP1, OP2, OP3, E0, E1;

        wire [0:3] Flag, aluFlag;

        reg [0:3] prev_Flag;

        wire [0:1] reg_src_A, reg_src_B, st_src;

        wire [0:2] load_hazard_abs;

        assign Type = ID_EX_reg[0:`type_msb];

        assign WB_Dest = ID_EX_reg[`type_msb+1:`type_msb+1+`wb_dst_msb];

        assign Module = ID_EX_reg[`type_msb+1+`wb_dst_msb+1:`type_msb+1+`wb_dst_msb+1+`mod_sel_msb];

        assign Operation = ID_EX_reg[`type_msb+1+`wb_dst_msb+1+`mod_sel_msb+1:`type_msb+1+`wb_dst_msb+1+`mod_sel_msb+1+`operation_msb];

        assign Rd_BC = ID_EX_reg[`type_msb+1+`wb_dst_msb+1+`mod_sel_msb+1+`operation_msb+1:`type_msb+1+`wb_dst_msb+1+`mod_sel_msb+1+`operation_msb+1+`bc_msb];

        assign OP1 = (reg_src_A[0] & load_hazard_abs[0]) | (reg_src_A[1] & ~load_hazard_abs[0]) ? b_MEM_WB_reg : (reg_src_A[0] & ~load_hazard_abs[0]) ? b_EX_MEM_reg : (reg_src_A[1] & load_hazard_abs[0]) ? bb_MEM_WB_reg : ID_EX_reg[`type_msb+1+`wb_dst_msb+1+`mod_sel_msb+1+`operation_msb+1+`bc_msb+`dpw+`dpw+3:`type_msb+1+`wb_dst_msb+1+`mod_sel_msb+1+`operation_msb+1+`bc_msb+`dpw+`dpw+3+`dpw];

        assign OP2 = (reg_src_B[0] & load_hazard_abs[1]) | (reg_src_B[1] & ~load_hazard_abs[1]) ? b_MEM_WB_reg : (reg_src_B[0] & ~load_hazard_abs[1]) ? b_EX_MEM_reg : (reg_src_B[1] & load_hazard_abs[1]) ? bb_MEM_WB_reg : ID_EX_reg[`type_msb+1+`wb_dst_msb+1+`mod_sel_msb+1+`operation_msb+1+`bc_msb+`dpw+2:`type_msb+1+`wb_dst_msb+1+`mod_sel_msb+1+`operation_msb+1+`bc_msb+`dpw+2+`dpw];

//      assign OP1 = reg_src_A[0] ? b_EX_MEM_reg : reg_src_A[1] ? load_hazard_abs[0] ? bb_MEM_WB_reg : b_MEM_WB_reg : ID_EX_reg[`type_msb+1+`mod_sel_msb+1+`operation_msb+1+`bc_msb+`dpw+`dpw+3:`type_msb+1+`mod_sel_msb+1+`operation_msb+1+`bc_msb+`dpw+`dpw+3+`dpw];

//      assign OP2 = reg_src_B[0] ? b_EX_MEM_reg : reg_src_B[1] ? load_hazard_abs[1] ? bb_MEM_WB_reg : b_MEM_WB_reg : ID_EX_reg[`type_msb+1+`mod_sel_msb+1+`operation_msb+1+`bc_msb+`dpw+2:`type_msb+1+`mod_sel_msb+1+`operation_msb+1+`bc_msb+`dpw+2+`dpw];

        assign reg_src_A = ID_EX_reg[`type_msb+1+`wb_dst_msb+1+`mod_sel_msb+1+`operation_msb+1+`bc_msb+1+`dpw+`dpw+`dpw+3:`type_msb+1+`wb_dst_msb+1+`mod_sel_msb+1+`operation_msb+1+`bc_msb+1+`dpw+`dpw+`dpw+4];

        assign reg_src_B = ID_EX_reg[`type_msb+1+`wb_dst_msb+1+`mod_sel_msb+1+`operation_msb+1+`bc_msb+1+`dpw+`dpw+`dpw+5:`type_msb+1+`wb_dst_msb+1+`mod_sel_msb+1+`operation_msb+1+`bc_msb+1+`dpw+`dpw+`dpw+6];

        assign st_src = ID_EX_reg[`type_msb+1+`wb_dst_msb+1+`mod_sel_msb+1+`operation_msb+1+`bc_msb+1+`dpw+`dpw+`dpw+7:`type_msb+1+`wb_dst_msb+1+`mod_sel_msb+1+`operation_msb+1+`bc_msb+1+`dpw+`dpw+`dpw+8];

        assign load_hazard_abs = ID_EX_reg[`type_msb+1+`wb_dst_msb+1+`mod_sel_msb+1+`operation_msb+1+`bc_msb+1+`dpw+`dpw+`dpw+9:`type_msb+1+`wb_dst_msb+1+`mod_sel_msb+1+`operation_msb+1+`bc_msb+1+`dpw+`dpw+`dpw+11];

        //----Sub Modules----//

        int_ALU int_ALU_inst(

                .Module(Module),

                .Operation(Operation),

                .OP1(OP1),

                .OP2(OP2),

                .Result(E1),

                .Flag(aluFlag),

                .prev_Flag(prev_Flag)

        );

        Shifter barrel_shifter_inst(

                .Module(Module),

                .Operation(Operation),

                .OP1(OP1),

                .OP2(OP2),

                .Result(E1)

        );

        assign Flag = ret ? stkFlag : aluFlag;

        assign stkFlag = ~ret ? Flag : 'bz;

        always@(posedge Clk) begin

                prev_Flag <= Flag;

                bb_MEM_WB_reg <= b_MEM_WB_reg; //store previous MEM_WB_reg coz we can't read it back from RF

        end

        assign E0 = (Type==`type_store) ? st_src[0] ? b_EX_MEM_reg : st_src[1] ? load_hazard_abs[2] ? bb_MEM_WB_reg : b_MEM_WB_reg : ID_EX_reg[`type_msb+1+`wb_dst_msb+1+`mod_sel_msb+1+`operation_msb+1+`bc_msb+1:`type_msb+1+`wb_dst_msb+1+`mod_sel_msb+1+`operation_msb+1+`bc_msb+1+`dpw] : (Type==`type_other) ? Flag : (Type==`type_branch) ? prev_Flag : 'bZ ;

        assign EX_MEM_reg = {Type,WB_Dest,Rd_BC,E0,E1};

endmodule