//////////////////////////////////////////////////////////////////////
////                                                              ////
////  CRC_chk.v                                                   ////
////                                                              ////
////  This file is part of the Ethernet IP core project           ////
////  http://www.opencores.org/projects.cgi/web/ethernet_tri_mode/////
////                                                              ////
////  Author(s):                                                  ////
////      - Jon Gao (gaojon@yahoo.com)                            ////
////                                                              ////
////                                                              ////
//////////////////////////////////////////////////////////////////////
////                                                              ////
//// 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: CRC_chk.v,v $
// Revision 1.3  2006/01/19 14:07:54  maverickist
// verification is complete.
//
// Revision 1.2  2005/12/16 06:44:16  Administrator
// replaced tab with space.
// passed 9.6k length frame test.
//
// Revision 1.1.1.1  2005/12/13 01:51:45  Administrator
// no message
//                                           

module CRC_chk(
Reset       ,
Clk         ,
CRC_data    ,
CRC_init    ,
CRC_en      ,
//From CPU  
CRC_chk_en  ,
CRC_err     
);
input       Reset       ;
input       Clk         ;
input[7:0]  CRC_data    ;
input       CRC_init    ;
input       CRC_en      ;
            //From CPU
input       CRC_chk_en  ;
output      CRC_err     ; 
//******************************************************************************   
//internal signals                                                              
//******************************************************************************
reg [31:0]  CRC_reg;
//******************************************************************************
//input data width is 8bit, and the first bit is bit[0]
function[31:0]  NextCRC;
    input[7:0]      D;
    input[31:0]     C;
    reg[31:0]       NewCRC;
    begin
    NewCRC[0]=C[24]^C[30]^D[1]^D[7];
    NewCRC[1]=C[25]^C[31]^D[0]^D[6]^C[24]^C[30]^D[1]^D[7];
    NewCRC[2]=C[26]^D[5]^C[25]^C[31]^D[0]^D[6]^C[24]^C[30]^D[1]^D[7];
    NewCRC[3]=C[27]^D[4]^C[26]^D[5]^C[25]^C[31]^D[0]^D[6];
    NewCRC[4]=C[28]^D[3]^C[27]^D[4]^C[26]^D[5]^C[24]^C[30]^D[1]^D[7];
    NewCRC[5]=C[29]^D[2]^C[28]^D[3]^C[27]^D[4]^C[25]^C[31]^D[0]^D[6]^C[24]^C[30]^D[1]^D[7];
    NewCRC[6]=C[30]^D[1]^C[29]^D[2]^C[28]^D[3]^C[26]^D[5]^C[25]^C[31]^D[0]^D[6];
    NewCRC[7]=C[31]^D[0]^C[29]^D[2]^C[27]^D[4]^C[26]^D[5]^C[24]^D[7];
    NewCRC[8]=C[0]^C[28]^D[3]^C[27]^D[4]^C[25]^D[6]^C[24]^D[7];
    NewCRC[9]=C[1]^C[29]^D[2]^C[28]^D[3]^C[26]^D[5]^C[25]^D[6];
    NewCRC[10]=C[2]^C[29]^D[2]^C[27]^D[4]^C[26]^D[5]^C[24]^D[7];
    NewCRC[11]=C[3]^C[28]^D[3]^C[27]^D[4]^C[25]^D[6]^C[24]^D[7];
    NewCRC[12]=C[4]^C[29]^D[2]^C[28]^D[3]^C[26]^D[5]^C[25]^D[6]^C[24]^C[30]^D[1]^D[7];
    NewCRC[13]=C[5]^C[30]^D[1]^C[29]^D[2]^C[27]^D[4]^C[26]^D[5]^C[25]^C[31]^D[0]^D[6];
    NewCRC[14]=C[6]^C[31]^D[0]^C[30]^D[1]^C[28]^D[3]^C[27]^D[4]^C[26]^D[5];
    NewCRC[15]=C[7]^C[31]^D[0]^C[29]^D[2]^C[28]^D[3]^C[27]^D[4];
    NewCRC[16]=C[8]^C[29]^D[2]^C[28]^D[3]^C[24]^D[7];
    NewCRC[17]=C[9]^C[30]^D[1]^C[29]^D[2]^C[25]^D[6];
    NewCRC[18]=C[10]^C[31]^D[0]^C[30]^D[1]^C[26]^D[5];
    NewCRC[19]=C[11]^C[31]^D[0]^C[27]^D[4];
    NewCRC[20]=C[12]^C[28]^D[3];
    NewCRC[21]=C[13]^C[29]^D[2];
    NewCRC[22]=C[14]^C[24]^D[7];
    NewCRC[23]=C[15]^C[25]^D[6]^C[24]^C[30]^D[1]^D[7];
    NewCRC[24]=C[16]^C[26]^D[5]^C[25]^C[31]^D[0]^D[6];
    NewCRC[25]=C[17]^C[27]^D[4]^C[26]^D[5];
    NewCRC[26]=C[18]^C[28]^D[3]^C[27]^D[4]^C[24]^C[30]^D[1]^D[7];
    NewCRC[27]=C[19]^C[29]^D[2]^C[28]^D[3]^C[25]^C[31]^D[0]^D[6];
    NewCRC[28]=C[20]^C[30]^D[1]^C[29]^D[2]^C[26]^D[5];
    NewCRC[29]=C[21]^C[31]^D[0]^C[30]^D[1]^C[27]^D[4];
    NewCRC[30]=C[22]^C[31]^D[0]^C[28]^D[3];
    NewCRC[31]=C[23]^C[29]^D[2];
    NextCRC=NewCRC;
    end
        endfunction

always @ (posedge Clk or posedge Reset)
    if (Reset)
        CRC_reg     <=32'hffffffff;
    else if (CRC_init)
        CRC_reg     <=32'hffffffff;
    else if (CRC_en)
        CRC_reg     <=NextCRC(CRC_data,CRC_reg);

assign  CRC_err = CRC_chk_en&(CRC_reg[31:0] != 32'hc704dd7b);

endmodule