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

////                                                              ////

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

////                                                              ////

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

////  http://www.opencores.org/cores/oms8051mini/                 ////

////                                                              ////

//// 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                     ////

////      - Dinesh Annayya, dinesha@opencores.org                 ////

////                                                              ////

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

////   v0.0 - Dinesh A, 5th Jan 2017

////        1. Active edge of reset changed from High to Low

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

////                                                              ////

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

////                                                              ////

//// 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                     ////

////                                                              ////

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

//

// CVS Revision History

//

// $Log: not supported by cvs2svn $

// Revision 1.18  2003/07/01 18:51:11  simont

// x replaced with 0.

//

// Revision 1.17  2003/06/09 16:51:16  simont

// fix bug in DA operation.

//

// Revision 1.16  2003/06/03 17:15:06  simont

// sub_result output added.

//

// Revision 1.15  2003/05/07 12:31:53  simont

// add wire sub_result, conect it to des_acc and des1.

//

// Revision 1.14  2003/05/05 15:46:36  simont

// add aditional alu destination to solve critical path.

//

// Revision 1.13  2003/04/29 08:35:12  simont

// fix bug in substraction.

//

// Revision 1.12  2003/04/25 17:15:51  simont

// change branch instruction execution (reduse needed clock periods).

//

// Revision 1.11  2003/04/14 14:29:42  simont

// fiz bug iv pcs operation.

//

// Revision 1.10  2003/01/13 14:14:40  simont

// replace some modules

//

// Revision 1.9  2002/09/30 17:33:59  simont

// prepared header

//

//

`include "top_defines.v"

module oc8051_alu (clk, resetn, op_code, src1, src2, src3, srcCy, srcAc, bit_in,

                  des1, des2, des_acc, desCy, desAc, desOv, sub_result);

//

// 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)

// des2         (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, resetn;

input  [3:0] op_code;

input  [7:0] src1, src2, src3;

output       desCy, desAc, desOv;

output [7:0] des1, des2, des_acc, sub_result;

reg desCy, desAc, desOv;

reg [7:0] des1, des2, des_acc;

//

//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;

wire [7:0] sub_result;

//

//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, da_tmp1;

//reg [8:0] da1;

//

// inc

//

wire [15:0] inc, dec;

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

oc8051_divide oc8051_div1(.clk(clk), .resetn(resetn), .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;

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

/* inc */

assign inc = {src2, src1} + {15'h0, 1'b1};

assign dec = {src2, src1} - {15'h0, 1'b1};

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 or inc or dec or sub_result)

begin

  case (op_code) /* synopsys full_case parallel_case */

//operation add

    `OC8051_ALU_ADD: begin

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

      des1 = src1;

      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

      des_acc = sub_result;

//      des1 = sub_result;

      des1 = 8'h00;

      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

      des_acc = mulsrc1;

      des1 = src1;

      des2 = mulsrc2;

      desOv = mulOv;

      desCy = 1'b0;

      desAc = 1'b0;

      enable_mul = 1'b1;

      enable_div = 1'b0;

    end

//operation divide

    `OC8051_ALU_DIV: begin

      des_acc = divsrc1;

      des1 = src1;

      des2 = divsrc2;

      desOv = divOv;

      desAc = 1'b0;

      desCy = 1'b0;

      enable_mul = 1'b0;

      enable_div = 1'b1;

    end

//operation decimal adjustment

    `OC8051_ALU_DA: begin

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

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

      if (srcCy | da_tmp | src1[7:4]>4'b1001)

        {da_tmp1, des_acc[7:4]} = {srcCy, src1[7:4]}+ 5'b00110 + {4'b0, da_tmp};

      else {da_tmp1, des_acc[7:4]} = {srcCy, src1[7:4]} + {4'b0, da_tmp};

      desCy = da_tmp | da_tmp1;

      des1 = src1;

      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

      des_acc = ~src1;

      des1 = ~src1;

      des2 = 8'h00;

      desCy = !srcCy;

      desAc = 1'b0;

      desOv = 1'b0;

      enable_mul = 1'b0;

      enable_div = 1'b0;

    end

//operation and

//bit operation and

    `OC8051_ALU_AND: begin

      des_acc = src1 & src2;

      des1 = src1 & src2;

      des2 = 8'h00;

      desCy = srcCy & bit_in;

      desAc = 1'b0;

      desOv = 1'b0;

      enable_mul = 1'b0;

      enable_div = 1'b0;

    end

//operation xor

// bit operation xor

    `OC8051_ALU_XOR: begin

      des_acc = src1 ^ src2;

      des1 = src1 ^ src2;

      des2 = 8'h00;

      desCy = srcCy ^ bit_in;

      desAc = 1'b0;

      desOv = 1'b0;

      enable_mul = 1'b0;

      enable_div = 1'b0;

    end

//operation or

// bit operation or

    `OC8051_ALU_OR: begin

      des_acc = src1 | src2;

      des1 = src1 | src2;

      des2 = 8'h00;

      desCy = srcCy | bit_in;

      desAc = 1'b0;

      desOv = 1'b0;

      enable_mul = 1'b0;

      enable_div = 1'b0;

    end

//operation rotate left

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

    `OC8051_ALU_RL: begin

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

      des1 = src1 ;

      des2 = 8'h00;

      desCy = srcCy | !bit_in;

      desAc = 1'b0;

      desOv = 1'b0;

      enable_mul = 1'b0;

      enable_div = 1'b0;

    end

//operation rotate left with carry and swap nibbles

    `OC8051_ALU_RLC: begin

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

      des1 = src1 ;

      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

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

      des1 = src1 ;

      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

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

      des1 = src1 ;

      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_INC: begin

      if (srcCy) begin

        des_acc = dec[7:0];

        des1 = dec[7:0];

        des2 = dec[15:8];

      end else begin

        des_acc = inc[7:0];

        des1 = inc[7:0];

        des2 = inc[15:8];

      end

      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

        des_acc = src2;

        des1 = src2;

        des2 = src1;

      end else begin

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

        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

    `OC8051_ALU_NOP: begin

      des_acc = src1;

      des1 = src1;

      des2 = src2;

      desCy = srcCy;

      desAc = srcAc;

      desOv = 1'b0;

      enable_mul = 1'b0;

      enable_div = 1'b0;

    end

  endcase

end

endmodule