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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 		  ////
//// 								  ////
//// 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, 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) first result [oc8051_pc.alu, oc8051_ram_top.wr_data, oc8051_acc.data_in, oc8051_b_register.data_in, oc8051_comp.des -r, oc8051_sp.data_in, oc8051_dptr.data_in, oc8051_psw.data_in, oc8051_indi_addr.data_in, oc8051_rom_addr_sel.des1, oc8051_ports.data_in]
// des2         (out) second result [oc8051_pc.alu, oc8051_rom_addr_sel.des1]
// 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;
 
  reg desCy, desAc, desOv;
  reg [7:0] des1, des2;
//
//add
//
  reg [4:0] add1, add2, add3, add4; reg [3:0] add5, add6, add7, add8; reg [1:0] add9, adda, addb, addc;
 
//
//sub
//
  reg [4:0] sub1, sub2, sub3, sub4; reg [3:0] sub5, sub6, sub7, sub8; reg [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));
 
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)
begin
 
  case (op_code)
//operation add
    `OC8051_ALU_ADD: begin
      add1 <= {1'b0,src1[3:0]};
      add2 <= {1'b0,src2[3:0]};
      add3 <= {3'b000,srcCy};
      add4 <= add1+add2+add3;
 
      add5 <= {1'b0,src1[6:4]};
      add6 <= {1'b0,src2[6:4]};
      add7 <= {1'b0,1'b0,1'b0,add4[4]};
      add8 <= add5+add6+add7;
 
      add9 <= {1'b0,src1[7]};
      adda <= {1'b0,src2[7]};
      addb <= {1'b0,add8[3]};
      addc <= add9+adda+addb;
 
      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
 
      sub1 <= {1'b1,src1[3:0]};
      sub2 <= {1'b0,src2[3:0]};
      sub3 <= {1'b0,1'b0,1'b0,srcCy};
      sub4 <= sub1-sub2-sub3;
 
      sub5 <= {1'b1,src1[6:4]};
      sub6 <= {1'b0,src2[6:4]};
      sub7 <= {1'b0,1'b0,1'b0, !sub4[4]};
      sub8 <= sub5-sub6-sub7;
 
      sub9 <= {1'b1,src1[7]};
      suba <= {1'b0,src2[7]};
      subb <= {1'b0,!sub8[3]};
      subc <= sub9-suba-subb;
 
      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
 
 
endmodule