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

////                                                              ////

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

////                                                              ////

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

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

////                                                              ////

//// Description                                                  ////

//// Two 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                         ////

////                                                              ////

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

////                                                              ////

//// 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

//

// ver: 2 markom

// changed nonsynthesizable version to two cycle divison

// 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

reg desOv;

wire div0, div1, div2, div3;

wire [7:0] rem1, rem2, rem3, rem4;

wire [15:0] cmp0, cmp1, cmp2, cmp3;

reg [7:0] div_out, rem_out;

wire [7:0] div;

// real registers

reg cycle;

reg [3:0] tmp_div;

reg [7:0] tmp_rem;

/* This logic is very much redundant, but it should be optimized by

   synthesizer */

assign cmp3 = src2 << (cycle ? 3'h7 : 3'h3);

assign cmp2 = src2 << (cycle ? 3'h6 : 3'h2);

assign cmp1 = src2 << (cycle ? 3'h5 : 3'h1);

assign cmp0 = src2 << (cycle ? 3'h4 : 3'h0);

assign rem4 = cycle ? tmp_rem : src1;

assign div3 = cmp3 <= rem4;

assign rem3 = rem4 - (div3 ? cmp3[7:0] : 8'h0);

assign div2 = cmp2 <= rem3;

assign rem2 = rem3 - (div2 ? cmp2[7:0] : 8'h0);

assign div1 = cmp1 <= rem2;

assign rem1 = rem2 - (div1 ? cmp1[7:0] : 8'h0);

assign div0 = cmp0 <= rem1;

//

// in clock cycle 0 we first calculate four MSB bits,

// and four LSB in cycle 1

always @(rem1 or div0 or div1 or div2 or div3 or cmp0 or tmp_div)

begin

  if (src2 == 8'h0) begin

    desOv = 1'b1;

    div_out = 8'hx;

    rem_out = 8'hx;

  end else begin

    desOv = 1'b0;

    rem_out = rem1 - (div0 ? cmp0[7:0] : 8'h0);

    div_out = {tmp_div, div3, div2, div1, div0};

  end

end

//

// divider works in two clock cycles -- 0 and 1

always @(posedge clk or posedge rst)

begin

  if (rst) begin

    cycle <= #1 1'b0;

    tmp_div <= #1 4'h0;

    tmp_rem <= #1 8'h0;

  end else begin

    if (enable && !cycle) cycle <= #1 1'b1;

    else cycle <= #1 1'b0;

    tmp_div <= #1 div_out[3:0];

    tmp_rem <= #1 rem_out;

  end

end

//

// assign outputs

assign des1 = rem_out;

assign des2 = div_out;

endmodule