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

////                                                              ////

//// alu for 8051 Core                                            ////

////                                                              ////

//// This file is part of the 8051 cores project                  ////

//// http://www.opencores.org/cores/8051/                         ////

////                                                              ////

//// Description                                                  ////

//// Implementation of aritmetic unit  according to               ////

//// 8051 IP core specification document. Uses divide.v and       ////

//// multiply.v                                                   ////

////                                                              ////

//// To Do:                                                       ////

////  pc signed add                                               ////

////                                                              ////

//// Author(s):                                                   ////

//// - Simon Teran, simont@opencores.org                          ////

////                                                              ////

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

////                                                              ////

//// Copyright (C) 2001 Authors and OPENCORES.ORG                 ////

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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  ////

//// the original copyright notice and the associated disclaimer. ////

////                                                              ////

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

//// and/or modify it under the terms of the GNU Lesser General   ////

//// Public License as published by the Free Software Foundation; ////

//// either version 2.1 of the License, or (at your option) any   ////

//// later version.                                               ////

////                                                              ////

//// This source is distributed in the hope that it will be       ////

//// useful, but WITHOUT ANY WARRANTY; without even the implied   ////

//// warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR      ////

//// PURPOSE. See the GNU Lesser General Public License for more  ////

//// details.                                                     ////

////                                                              ////

//// You should have received a copy of the GNU Lesser General    ////

//// Public License along with this source; if not, download it   ////

//// from http://www.opencores.org/lgpl.shtml                     ////

////                                                              ////

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

//

// ver: 1

//

// synopsys translate_off

`include "oc8051_timescale.v"

// synopsys translate_on

`include "oc8051_defines.v"

module oc8051_alu (clk, rst, op_code, src1, src2, src3, srcCy, srcAc, bit_in, des1, des2, des1_r, des2_r, desCy, desAc, desOv);

//

// op_code      (in)  operation code [oc8051_decoder.alu_op -r]

// src1         (in)  first operand [oc8051_alu_src1_sel.des]

// src2         (in)  second operand [oc8051_alu_src2_sel.des]

// src3         (in)  third operand [oc8051_alu_src3_sel.des]

// srcCy        (in)  carry input [oc8051_cy_select.data_out]

// srcAc        (in)  auxiliary carry input [oc8051_psw.data_out[6] ]

// bit_in       (in)  bit input, used for logic operatins on bits [oc8051_ram_sel.bit_out]

// des1         (out) 

// des1_r       (out)

// des2         (out)

// des2_r       (out)

// desCy        (out) carry output [oc8051_ram_top.bit_data_in, oc8051_acc.bit_in, oc8051_b_register.bit_in, oc8051_psw.cy_in, oc8051_ports.bit_in]

// desAc        (out) auxiliary carry output [oc8051_psw.ac_in]

// desOv        (out) Overflow output [oc8051_psw.ov_in]

//

input srcCy, srcAc, bit_in, clk, rst; input [3:0] op_code; input [7:0] src1, src2, src3;

output desCy, desAc, desOv;

output [7:0] des1, des2;

output [7:0] des1_r, des2_r;

reg desCy, desAc, desOv;

reg [7:0] des1, des2;

reg [7:0] des1_r, des2_r;

//

//add

//

wire [4:0] add1, add2, add3, add4;

wire [3:0] add5, add6, add7, add8;

wire [1:0] add9, adda, addb, addc;

//

//sub

//

wire [4:0] sub1, sub2, sub3, sub4;

wire [3:0] sub5, sub6, sub7, sub8;

wire [1:0] sub9, suba, subb, subc;

//

//mul

//

  wire [7:0] mulsrc1, mulsrc2;

  wire mulOv;

  reg enable_mul;

//

//div

//

wire [7:0] divsrc1,divsrc2;

wire divOv;

reg enable_div;

//

//da

//

reg da_tmp;

//reg [8:0] da1;

oc8051_multiply oc8051_mul1(.clk(clk), .rst(rst), .enable(enable_mul), .src1(src1), .src2(src2), .des1(mulsrc1), .des2(mulsrc2), .desOv(mulOv));

oc8051_divide oc8051_div1(.clk(clk), .rst(rst), .enable(enable_div), .src1(src1), .src2(src2), .des1(divsrc1), .des2(divsrc2), .desOv(divOv));

/* Add */

assign add1 = {1'b0,src1[3:0]};

assign add2 = {1'b0,src2[3:0]};

assign add3 = {3'b000,srcCy};

assign add4 = add1+add2+add3;

assign add5 = {1'b0,src1[6:4]};

assign add6 = {1'b0,src2[6:4]};

assign add7 = {1'b0,1'b0,1'b0,add4[4]};

assign add8 = add5+add6+add7;

assign add9 = {1'b0,src1[7]};

assign adda = {1'b0,src2[7]};

assign addb = {1'b0,add8[3]};

assign addc = add9+adda+addb;

/* Sub */

assign sub1 = {1'b1,src1[3:0]};

assign sub2 = {1'b0,src2[3:0]};

assign sub3 = {1'b0,1'b0,1'b0,srcCy};

assign sub4 = sub1-sub2-sub3;

assign sub5 = {1'b1,src1[6:4]};

assign sub6 = {1'b0,src2[6:4]};

assign sub7 = {1'b0,1'b0,1'b0, !sub4[4]};

assign sub8 = sub5-sub6-sub7;

assign sub9 = {1'b1,src1[7]};

assign suba = {1'b0,src2[7]};

assign subb = {1'b0,!sub8[3]};

assign subc = sub9-suba-subb;

always @(op_code or src1 or src2 or srcCy or srcAc or bit_in or src3 or mulsrc1 or mulsrc2 or mulOv or divsrc1 or divsrc2 or divOv or addc or add8 or add4 or sub4 or sub8 or subc or da_tmp)

begin

  case (op_code)

//operation add

    `OC8051_ALU_ADD: begin

      des1 = {addc[0],add8[2:0],add4[3:0]};

      des2 = src3+ {7'b0, addc[1]};

      desCy = addc[1];

      desAc = add4[4];

      desOv = addc[1] ^ add8[3];

      enable_mul = 1'b0;

      enable_div = 1'b0;

    end

//operation subtract

    `OC8051_ALU_SUB: begin

      des1 = {subc[0],sub8[2:0],sub4[3:0]};

      des2 = 8'h00;

      desCy = !subc[1];

      desAc = !sub4[4];

      desOv = !subc[1] ^ sub8[3];

      enable_mul = 1'b0;

      enable_div = 1'b0;

    end

//operation multiply

    `OC8051_ALU_MUL: begin

      des1 = mulsrc2;

      des2 = mulsrc1;

      desOv = mulOv;

      desCy = 1'b0;

      desAc = 1'bx;

      enable_mul = 1'b1;

      enable_div = 1'b0;

    end

//operation divide

    `OC8051_ALU_DIV: begin

      des1 = divsrc2;

      des2 = divsrc1;

      desOv = divOv;

      desAc = 1'bx;

      desCy = 1'b0;

      enable_mul = 1'b0;

      enable_div = 1'b1;

    end

//operation decimal adjustment

    `OC8051_ALU_DA: begin

/*      da1= {1'b0, src1};

      if (srcAc==1'b1 | da1[3:0]>4'b1001) da1= da1+ 9'b0_0000_0110;

      da1[8]= da1[8] | srcCy;

      if (da1[8]==1'b1) da1=da1+ 9'b0_0110_0000;

      des1=da1[7:0];

      des2=8'h00;

      desCy=da1[8];*/

      if (srcAc==1'b1 | src1[3:0]>4'b1001) {da_tmp, des1[3:0]} = {1'b0, src1[3:0]}+ 5'b00110;

      else {da_tmp, des1[3:0]} = {1'b0, src1[3:0]};

      if (srcCy==1'b1 | src1[7:4]>4'b1001)

        {desCy, des1[7:4]} = {srcCy, src1[7:4]}+ 5'b00110 + {4'b0, da_tmp};

      else {desCy, des1[7:4]} = {srcCy, src1[7:4]} + {4'b0, da_tmp};

      des2 = 8'h00;

      desAc = 1'b0;

      desOv = 1'b0;

      enable_mul = 1'b0;

      enable_div = 1'b0;

    end

//operation not

// bit operation not

    `OC8051_ALU_NOT: begin

      des1 = ~src1;

      des2 = 8'h00;

      desCy = !srcCy;

      desAc = 1'bx;

      desOv = 1'bx;

      enable_mul = 1'b0;

      enable_div = 1'b0;

    end

//operation and

//bit operation and

    `OC8051_ALU_AND: begin

      des1 = src1 & src2;

      des2 = 8'h00;

      desCy = srcCy & bit_in;

      desAc = 1'bx;

      desOv = 1'bx;

      enable_mul = 1'b0;

      enable_div = 1'b0;

    end

//operation xor

// bit operation xor

    `OC8051_ALU_XOR: begin

      des1 = src1 ^ src2;

      des2 = 8'h00;

      desCy = srcCy ^ bit_in;

      desAc = 1'bx;

      desOv = 1'bx;

      enable_mul = 1'b0;

      enable_div = 1'b0;

    end

//operation or

// bit operation or

    `OC8051_ALU_OR: begin

      des1 = src1 | src2;

      des2 = 8'h00;

      desCy = srcCy | bit_in;

      desAc = 1'bx;

      desOv = 1'bx;

      enable_mul = 1'b0;

      enable_div = 1'b0;

    end

//operation rotate left

// bit operation cy= cy or (not ram)

    `OC8051_ALU_RL: begin

      des1 = {src1[6:0], src1[7]};

      des2 = 8'h00;

      desCy = srcCy | !bit_in;

      desAc = 1'bx;

      desOv = 1'bx;

      enable_mul = 1'b0;

      enable_div = 1'b0;

    end

//operation rotate left with carry and swap nibbles

    `OC8051_ALU_RLC: begin

      des1 = {src1[6:0], srcCy};

      des2 = {src1[3:0], src1[7:4]};

      desCy = src1[7];

      desAc = 1'b0;

      desOv = 1'b0;

      enable_mul = 1'b0;

      enable_div = 1'b0;

    end

//operation rotate right

    `OC8051_ALU_RR: begin

      des1 = {src1[0], src1[7:1]};

      des2 = 8'h00;

      desCy = srcCy & !bit_in;

      desAc = 1'b0;

      desOv = 1'b0;

      enable_mul = 1'b0;

      enable_div = 1'b0;

    end

//operation rotate right with carry

    `OC8051_ALU_RRC: begin

      des1 = {srcCy, src1[7:1]};

      des2 = 8'h00;

      desCy = src1[0];

      desAc = 1'b0;

      desOv = 1'b0;

      enable_mul = 1'b0;

      enable_div = 1'b0;

    end

//operation pcs Add

    `OC8051_ALU_PCS: begin

       case (src1[7])

        1'b1: begin

          des1 = src2+src1;

          des2 = src3;

        end

        default: {des2, des1} = {src3,src2} + {8'h00, src1};

      endcase

      desCy = 1'b0;

      desAc = 1'b0;

      desOv = 1'b0;

      enable_mul = 1'b0;

      enable_div = 1'b0;

    end

//operation exchange

//if carry = 0 exchange low order digit

    `OC8051_ALU_XCH: begin

      if (srcCy)

      begin

        des1 = src2;

        des2 = src1;

      end else begin

        des1 = {src1[7:4],src2[3:0]};

        des2 = {src2[7:4],src1[3:0]};

      end

      desCy = 1'b0;

      desAc = 1'b0;

      desOv = 1'b0;

      enable_mul = 1'b0;

      enable_div = 1'b0;

    end

    default: begin

      des1 = src1;

      des2 = src2;

      desCy = srcCy;

      desAc = srcAc;

      desOv = 1'bx;

      enable_mul = 1'b0;

      enable_div = 1'b0;

    end

  endcase

end

always @(posedge clk or posedge rst)

  if (rst) begin

    des1_r <= #1 8'h0;

    des2_r <= #1 8'h0;

  end else begin

    des1_r <= #1 des1;

    des2_r <= #1 des2;

  end

endmodule