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////  eth_clockgen.v                                              ////

////                                                              ////

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

////  http://www.opencores.org/projects/ethmac/                   ////

////                                                              ////

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

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

////                                                              ////

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

////  file.                                                       ////

////                                                              ////

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//// 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. ////

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//// 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.                                               ////

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//// 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 1.4  2005/02/21 12:48:05  igorm

// Warning fixes.

//

// 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  2001/06/01 22:28:55  mohor

// This files (MIIM) are fully working. They were thoroughly tested. The testbench is not updated.

//

//

`include "timescale.v"

module eth_clockgen(Clk, Reset, Divider, MdcEn, MdcEn_n, Mdc);

parameter Tp=1;

input       Clk;              // Input clock (Host clock)

input       Reset;            // Reset signal

input [7:0] Divider;          // Divider (input clock will be divided by the Divider[7:0])

output      Mdc;              // Output clock

output      MdcEn;            // Enable signal is asserted for one Clk period before Mdc rises.

output      MdcEn_n;          // Enable signal is asserted for one Clk period before Mdc falls.

reg         Mdc;

reg   [7:0] Counter;

wire        CountEq0;

wire  [7:0] CounterPreset;

wire  [7:0] TempDivider;

assign TempDivider[7:0]   = (Divider[7:0]<2)? 8'h02 : Divider[7:0]; // If smaller than 2

assign CounterPreset[7:0] = (TempDivider[7:0]>>1) - 1'b1;           // We are counting half of period

// Counter counts half period

always @ (posedge Clk or posedge Reset)

begin

  if(Reset)

    Counter[7:0] <= #Tp 8'h1;

  else

    begin

      if(CountEq0)

        begin

          Counter[7:0] <= #Tp CounterPreset[7:0];

        end

      else

        Counter[7:0] <= #Tp Counter - 8'h1;

    end

end

// Mdc is asserted every other half period

always @ (posedge Clk or posedge Reset)

begin

  if(Reset)

    Mdc <= #Tp 1'b0;

  else

    begin

      if(CountEq0)

        Mdc <= #Tp ~Mdc;

    end

end

assign CountEq0 = Counter == 8'h0;

assign MdcEn = CountEq0 & ~Mdc;

assign MdcEn_n = CountEq0 & Mdc;

endmodule