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//// divide for 8051 Core                                         ////

////                                                              ////

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

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

////                                                              ////

//// Description                                                  ////

//// Four cycle implementation of division used in alu.v          ////

////                                                              ////

//// To Do:                                                       ////

////  check if compiler does proper optimizations of the code     ////

////                                                              ////

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

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

//// - Marko Mlinar, markom@opencores.org                         ////

////                                                              ////

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//// 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                     ////

////                                                              ////

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//

// CVS Revision History

//

// $Log: not supported by cvs2svn $

// Revision 1.8  2002/09/30 17:15:31  simont

// prepared header

//

//

// synopsys translate_off

`include "oc8051_timescale.v"

// synopsys translate_on

module oc8051_divide (clk, rst, enable, src1, src2, des1, des2, desOv);

//

// this module is part of alu

// clk          (in)

// rst          (in)

// enable       (in)  starts divison

// src1         (in)  first operand

// src2         (in)  second operand

// des1         (out) first result

// des2         (out) second result

// desOv        (out) Overflow output

//

input clk, rst, enable;

input [7:0] src1, src2;

output desOv;

output [7:0] des1, des2;

// wires

wire desOv;

wire div0, div1;

wire [7:0] rem0, rem1, rem2;

wire [8:0] sub0, sub1;

wire [15:0] cmp0, cmp1;

wire [7:0] div_out, rem_out;

// real registers

reg [1:0] cycle;

reg [5:0] tmp_div;

reg [7:0] tmp_rem;

// The main logic

assign cmp1 = src2 << ({2'h3 - cycle, 1'b0} + 3'h1);

assign cmp0 = src2 << ({2'h3 - cycle, 1'b0} + 3'h0);

assign rem2 = cycle != 0 ? tmp_rem : src1;

assign sub1 = {1'b0, rem2} - {1'b0, cmp1[7:0]};

assign div1 = |cmp1[15:8] ? 1'b0 : !sub1[8];

assign rem1 = div1 ? sub1[7:0] : rem2[7:0];

assign sub0 = {1'b0, rem1} - {1'b0, cmp0[7:0]};

assign div0 = |cmp0[15:8] ? 1'b0 : !sub0[8];

assign rem0 = div0 ? sub0[7:0] : rem1[7:0];

//

// in clock cycle 0 we first calculate two MSB bits, ...

// till finally in clock cycle 3 we calculate two LSB bits

assign div_out = {tmp_div, div1, div0};

assign rem_out = rem0;

assign desOv = src2 == 8'h0;

//

// divider works in four clock cycles -- 0, 1, 2 and 3

always @(posedge clk or posedge rst)

begin

  if (rst) begin

    cycle <= #1 2'b0;

    tmp_div <= #1 6'h0;

    tmp_rem <= #1 8'h0;

  end else begin

    if (enable) cycle <= #1 cycle + 2'b1;

    tmp_div <= #1 div_out[5:0];

    tmp_rem <= #1 rem_out;

  end

end

//

// assign outputs

assign des1 = rem_out;

assign des2 = div_out;

endmodule