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////  Ramdon_gen.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)                            ////

////                                                              ////

////                                                              ////

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//// Copyright (C) 2001 Authors                                   ////

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//// 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. ////

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//// 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       ////

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//// PURPOSE.  See the GNU Lesser General Public License for more ////

//// details.                                                     ////

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//// from http://www.opencores.org/lgpl.shtml                     ////

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//////////////////////////////////////////////////////////////////////

//                                                                    

// CVS Revision History                                               

//                                                                    

// $Log: not supported by cvs2svn $

// Revision 1.2  2005/12/16 06:44:19  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 Ramdon_gen(

Reset           ,

Clk             ,

Init            ,

RetryCnt        ,

Random_time_meet

);

input           Reset           ;

input           Clk             ;

input           Init            ;

input   [3:0]   RetryCnt        ;

output          Random_time_meet;

//******************************************************************************

//internal signals                                                              

//******************************************************************************

reg [9:0]       Random_sequence ;

reg [9:0]       Ramdom          ;

reg [9:0]       Ramdom_counter  ;

reg [7:0]       Slot_time_counter; //256*2=512bit=1 slot time

reg             Random_time_meet;

//******************************************************************************

always @ (posedge Clk or posedge Reset)

    if (Reset)

        Random_sequence     <=0;

    else

        Random_sequence     <={Random_sequence[8:0],~(Random_sequence[2]^Random_sequence[9])};

always @ (RetryCnt or Random_sequence)

    case (RetryCnt)

        4'h0    :   Ramdom={9'b0,Random_sequence[0]};

        4'h1    :   Ramdom={8'b0,Random_sequence[1:0]};

        4'h2    :   Ramdom={7'b0,Random_sequence[2:0]};

        4'h3    :   Ramdom={6'b0,Random_sequence[3:0]};

        4'h4    :   Ramdom={5'b0,Random_sequence[4:0]};

        4'h5    :   Ramdom={4'b0,Random_sequence[5:0]};

        4'h6    :   Ramdom={3'b0,Random_sequence[6:0]};

        4'h7    :   Ramdom={2'b0,Random_sequence[7:0]};

        4'h8    :   Ramdom={1'b0,Random_sequence[8:0]};

        4'h9    :   Ramdom={     Random_sequence[9:0]};

        default :   Ramdom={     Random_sequence[9:0]};

    endcase

always @ (posedge Clk or posedge Reset)

    if (Reset)

        Slot_time_counter       <=0;

    else if(Init)

        Slot_time_counter       <=0;

    else if(!Random_time_meet)

        Slot_time_counter       <=Slot_time_counter+1;

always @ (posedge Clk or posedge Reset)

    if (Reset)

        Ramdom_counter      <=0;

    else if (Init)

        Ramdom_counter      <=Ramdom;

    else if (Ramdom_counter!=0&&Slot_time_counter==255)

        Ramdom_counter      <=Ramdom_counter -1 ;

always @ (posedge Clk or posedge Reset)

    if (Reset)

        Random_time_meet    <=1;

    else if (Init)

        Random_time_meet    <=0;

    else if (Ramdom_counter==0)

        Random_time_meet    <=1;

endmodule