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

////                                                              ////

////  eth_random.v                                                ////

////                                                              ////

////  This file is part of the Ethernet IP core project           ////

////  http://www.opencores.org/project,ethmac                   ////

////                                                              ////

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

////      - Igor Mohor (igorM@opencores.org)                      ////

////      - Novan Hartadi (novan@vlsi.itb.ac.id)                  ////

////      - Mahmud Galela (mgalela@vlsi.itb.ac.id)                ////

////                                                              ////

////  All additional information is avaliable in the Readme.txt   ////

////  file.                                                       ////

////                                                              ////

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

////                                                              ////

//// Copyright (C) 2001 Authors                                   ////

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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                     ////

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

//

// CVS Revision History

//

// $Log: not supported by cvs2svn $

// Revision 1.3  2002/01/23 10:28:16  mohor

// Link in the header changed.

//

// Revision 1.2  2001/10/19 08:43:51  mohor

// eth_timescale.v changed to timescale.v This is done because of the

// simulation of the few cores in a one joined project.

//

// Revision 1.1  2001/08/06 14:44:29  mohor

// A define FPGA added to select between Artisan RAM (for ASIC) and Block Ram (For Virtex).

// Include files fixed to contain no path.

// File names and module names changed ta have a eth_ prologue in the name.

// File eth_timescale.v is used to define timescale

// All pin names on the top module are changed to contain _I, _O or _OE at the end.

// Bidirectional signal MDIO is changed to three signals (Mdc_O, Mdi_I, Mdo_O

// and Mdo_OE. The bidirectional signal must be created on the top level. This

// is done due to the ASIC tools.

//

// Revision 1.1  2001/07/30 21:23:42  mohor

// Directory structure changed. Files checked and joind together.

//

// Revision 1.3  2001/06/19 18:16:40  mohor

// TxClk changed to MTxClk (as discribed in the documentation).

// Crc changed so only one file can be used instead of two.

//

// Revision 1.2  2001/06/19 10:38:07  mohor

// Minor changes in header.

//

// Revision 1.1  2001/06/19 10:27:57  mohor

// TxEthMAC initial release.

//

//

//

//

`include "timescale.v"

module eth_random (MTxClk, Reset, StateJam, StateJam_q, RetryCnt, NibCnt, ByteCnt,

                   RandomEq0, RandomEqByteCnt);

parameter Tp = 1;

input MTxClk;

input Reset;

input StateJam;

input StateJam_q;

input [3:0] RetryCnt;

input [15:0] NibCnt;

input [9:0] ByteCnt;

output RandomEq0;

output RandomEqByteCnt;

wire Feedback;

reg [9:0] x;

wire [9:0] Random;

reg  [9:0] RandomLatched;

always @ (posedge MTxClk or posedge Reset)

begin

  if(Reset)

    x[9:0] <=  0;

  else

    x[9:0] <=  {x[8:0], Feedback};

end

assign Feedback = ~(x[2] ^ x[9]);

assign Random [0] = x[0];

assign Random [1] = (RetryCnt > 1) ? x[1] : 1'b0;

assign Random [2] = (RetryCnt > 2) ? x[2] : 1'b0;

assign Random [3] = (RetryCnt > 3) ? x[3] : 1'b0;

assign Random [4] = (RetryCnt > 4) ? x[4] : 1'b0;

assign Random [5] = (RetryCnt > 5) ? x[5] : 1'b0;

assign Random [6] = (RetryCnt > 6) ? x[6] : 1'b0;

assign Random [7] = (RetryCnt > 7) ? x[7] : 1'b0;

assign Random [8] = (RetryCnt > 8) ? x[8] : 1'b0;

assign Random [9] = (RetryCnt > 9) ? x[9] : 1'b0;

always @ (posedge MTxClk or posedge Reset)

begin

  if(Reset)

    RandomLatched <=  10'h000;

  else

    begin

      if(StateJam & StateJam_q)

        RandomLatched <=  Random;

    end

end

// Random Number == 0      IEEE 802.3 page 68. If 0 we go to defer and not to backoff.

assign RandomEq0 = RandomLatched == 10'h0;

assign RandomEqByteCnt = ByteCnt[9:0] == RandomLatched & (&NibCnt[6:0]);

endmodule