互联网MAC层CRC32 生成器

// Module Name: eth_mac_rx
// Project Name: 
// Target Devices: 
// Tool Versions: 
// Description: 
// 
// Dependencies: 
// 
// Revision:
// Revision 0.01 - File Created
// Additional Comments:
// 互联网MAC层 CRC32 生成器 Verilog 代码
//////////////////////////////////////////////////////////////////////////////////
module CRC_gen 
(
    input           clk,
    input           init,
    input   [7:0]   frame_data,
    input           data_en,
    input           crc_rd ,
    
    output  [7:0]   crc_out,
    output          crc_end,

    input           rst
);

//=======================================================================   
//internal signals                                                              
//=======================================================================   
reg [7:0]       crc_out;
reg [31:0]      crc_reg;
reg             crc_end;
reg [3:0]       counter;
//=======================================================================   
//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 rst)
if (rst)            crc_reg <= 32'hffffffff;
else if (init)      crc_reg <= 32'hffffffff;
else if (data_en)   crc_reg <= NextCRC(frame_data,crc_reg);
else if (crc_rd)    crc_reg <= {crc_reg[23:0],8'hff};


always @ (crc_rd or crc_reg)
if (crc_rd)
    crc_out <= ~{crc_reg[24],crc_reg[25],crc_reg[26],crc_reg[27],crc_reg[28],crc_reg[29],crc_reg[30],crc_reg[31]};
else
    crc_out <= 0;
        
//caculate CRC out length ,4 cycles     
//CRC_end aligned to last CRC checksum data
always @(posedge clk or posedge rst)
if (rst)    counter <= 0;
else if (!crc_rd)    counter <= 0;
else     counter <= counter + 1;
        
always @ (counter)
if (counter == 3) crc_end = 1;
else crc_end = 0;
//=======================================================================   
endmodule