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//////////////////////////////////////////////////////////////////////
////                                                              ////
////  eth_crc.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                                   ////
////                                                              ////
//// 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                     ////
////                                                              ////
//////////////////////////////////////////////////////////////////////
//
// CVS Revision History
//
// $Log: not supported by cvs2svn $
// 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_crc (Clk, Reset, Data, Enable, Initialize, Crc, CrcError);
 
 
input Clk;
input Reset;
input [3:0] Data;
input Enable;
input Initialize;
 
output [31:0] Crc;
output CrcError;
 
reg  [31:0] Crc;
 
wire [31:0] CrcNext;
 
 
assign CrcNext[0] = Enable & (Data[0] ^ Crc[28]); 
assign CrcNext[1] = Enable & (Data[1] ^ Data[0] ^ Crc[28] ^ Crc[29]); 
assign CrcNext[2] = Enable & (Data[2] ^ Data[1] ^ Data[0] ^ Crc[28] ^ Crc[29] ^ Crc[30]); 
assign CrcNext[3] = Enable & (Data[3] ^ Data[2] ^ Data[1] ^ Crc[29] ^ Crc[30] ^ Crc[31]); 
assign CrcNext[4] = (Enable & (Data[3] ^ Data[2] ^ Data[0] ^ Crc[28] ^ Crc[30] ^ Crc[31])) ^ Crc[0]; 
assign CrcNext[5] = (Enable & (Data[3] ^ Data[1] ^ Data[0] ^ Crc[28] ^ Crc[29] ^ Crc[31])) ^ Crc[1]; 
assign CrcNext[6] = (Enable & (Data[2] ^ Data[1] ^ Crc[29] ^ Crc[30])) ^ Crc[ 2]; 
assign CrcNext[7] = (Enable & (Data[3] ^ Data[2] ^ Data[0] ^ Crc[28] ^ Crc[30] ^ Crc[31])) ^ Crc[3]; 
assign CrcNext[8] = (Enable & (Data[3] ^ Data[1] ^ Data[0] ^ Crc[28] ^ Crc[29] ^ Crc[31])) ^ Crc[4]; 
assign CrcNext[9] = (Enable & (Data[2] ^ Data[1] ^ Crc[29] ^ Crc[30])) ^ Crc[5]; 
assign CrcNext[10] = (Enable & (Data[3] ^ Data[2] ^ Data[0] ^ Crc[28] ^ Crc[30] ^ Crc[31])) ^ Crc[6]; 
assign CrcNext[11] = (Enable & (Data[3] ^ Data[1] ^ Data[0] ^ Crc[28] ^ Crc[29] ^ Crc[31])) ^ Crc[7]; 
assign CrcNext[12] = (Enable & (Data[2] ^ Data[1] ^ Data[0] ^ Crc[28] ^ Crc[29] ^ Crc[30])) ^ Crc[8]; 
assign CrcNext[13] = (Enable & (Data[3] ^ Data[2] ^ Data[1] ^ Crc[29] ^ Crc[30] ^ Crc[31])) ^ Crc[9]; 
assign CrcNext[14] = (Enable & (Data[3] ^ Data[2] ^ Crc[30] ^ Crc[31])) ^ Crc[10]; 
assign CrcNext[15] = (Enable & (Data[3] ^ Crc[31])) ^ Crc[11]; 
assign CrcNext[16] = (Enable & (Data[0] ^ Crc[28])) ^ Crc[12]; 
assign CrcNext[17] = (Enable & (Data[1] ^ Crc[29])) ^ Crc[13]; 
assign CrcNext[18] = (Enable & (Data[2] ^ Crc[30])) ^ Crc[14]; 
assign CrcNext[19] = (Enable & (Data[3] ^ Crc[31])) ^ Crc[15]; 
assign CrcNext[20] = Crc[16]; 
assign CrcNext[21] = Crc[17]; 
assign CrcNext[22] = (Enable & (Data[0] ^ Crc[28])) ^ Crc[18]; 
assign CrcNext[23] = (Enable & (Data[1] ^ Data[0] ^ Crc[29] ^ Crc[28])) ^ Crc[19]; 
assign CrcNext[24] = (Enable & (Data[2] ^ Data[1] ^ Crc[30] ^ Crc[29])) ^ Crc[20]; 
assign CrcNext[25] = (Enable & (Data[3] ^ Data[2] ^ Crc[31] ^ Crc[30])) ^ Crc[21]; 
assign CrcNext[26] = (Enable & (Data[3] ^ Data[0] ^ Crc[31] ^ Crc[28])) ^ Crc[22]; 
assign CrcNext[27] = (Enable & (Data[1] ^ Crc[29])) ^ Crc[23]; 
assign CrcNext[28] = (Enable & (Data[2] ^ Crc[30])) ^ Crc[24]; 
assign CrcNext[29] = (Enable & (Data[3] ^ Crc[31])) ^ Crc[25]; 
assign CrcNext[30] = Crc[26]; 
assign CrcNext[31] = Crc[27]; 
 
 
always @ (posedge Clk or posedge Reset)
begin
  if (Reset)
    Crc <=  32'hffffffff;
  else
  if(Initialize)
    Crc <=  32'hffffffff;
  else
    Crc <=  CrcNext;
end
 
assign CrcError = Crc[31:0] != 32'hc704dd7b;  // CRC not equal to magic number
 
endmodule