以太网CRC校验代码问题

谁枫而飘 · 发表于 2016-8-25 10:24:18

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//////////////////////////////////////////////////////////////////////
//// ////
//// 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: not supported by cvs2svn $
// 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;
wire[31:0] Next_CRC;
//******************************************************************************
//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

复制代码

最后一行代码是怎么回事？他是怎么实现CRC校验的

masaka_xlw · 发表于 2016-8-26 07:46:09

这是CRC parallel algorithm。最后一行的意思就是如果CRC的parity不同于这数，就报错，用于固定存储数据。

谁枫而飘 · 发表于 2016-8-27 10:37:48

回复 2# masaka_xlw

看了，这是所谓的magic number

[求助] 以太网CRC校验代码问题

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