source: XOpenSparcT1/trunk/OC-Ethernet/eth_clockgen.v @ 6

//////////////////////////////////////////////////////////////////////
////                                                              ////
////  eth_clockgen.v                                              ////
////                                                              ////
////  This file is part of the Ethernet IP core project           ////
////  http://www.opencores.org/projects/ethmac/                   ////
////                                                              ////
////  Author(s):                                                  ////
////      - Igor Mohor ([email protected])                      ////
////                                                              ////
////  All additional information is avaliable in the Readme.txt   ////
////  file.                                                       ////
////                                                              ////
//////////////////////////////////////////////////////////////////////
////                                                              ////
//// Copyright (C) 2001 Authors                                   ////
////                                                              ////
//// 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.                                               ////
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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 1.3  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