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

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////  eth_shiftreg.v                                              ////

////                                                              ////

////  This file is part of the Ethernet IP core project           ////

////  http://www.opencores.org/project,ethmac                     ////

////                                                              ////

////  Author(s):                                                  ////

////      - Igor Mohor (igorM@opencores.org)                      ////

////                                                              ////

////  All additional information is avaliable in the Readme.txt   ////

////  file.                                                       ////

////                                                              ////

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

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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       ////

//// 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.                                                     ////

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//// 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                     ////

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

//

// CVS Revision History

//

// $Log: not supported by cvs2svn $

// Revision 1.5  2002/08/14 18:16:59  mohor

// LinkFail signal was not latching appropriate bit.

//

// Revision 1.4  2002/03/02 21:06:01  mohor

// LinkFail signal was not latching appropriate bit.

//

// Revision 1.3  2002/01/23 10:28:16  mohor

// Link in the header changed.

//

// 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  2001/06/01 22:28:56  mohor

// This files (MIIM) are fully working. They were thoroughly tested. The testbench is not updated.

//

//

`include "timescale.v"

module eth_shiftreg(Clk, Reset, MdcEn_n, Mdi, Fiad, Rgad, CtrlData, WriteOp, ByteSelect,

                    LatchByte, ShiftedBit, Prsd, LinkFail);

input       Clk;              // Input clock (Host clock)

input       Reset;            // Reset signal

input       MdcEn_n;          // Enable signal is asserted for one Clk period before Mdc falls.

input       Mdi;              // MII input data

input [4:0] Fiad;             // PHY address

input [4:0] Rgad;             // Register address (within the selected PHY)

input [15:0]CtrlData;         // Control data (data to be written to the PHY)

input       WriteOp;          // The current operation is a PHY register write operation

input [3:0] ByteSelect;       // Byte select

input [1:0] LatchByte;        // Byte select for latching (read operation)

output      ShiftedBit;       // Bit shifted out of the shift register

output[15:0]Prsd;             // Read Status Data (data read from the PHY)

output      LinkFail;         // Link Integrity Signal

reg   [7:0] ShiftReg;         // Shift register for shifting the data in and out

reg   [15:0]Prsd;

reg         LinkFail;

// ShiftReg[7:0] :: Shift Register Data

always @ (posedge Clk or posedge Reset)

begin

  if(Reset)

    begin

      ShiftReg[7:0] <=  8'h0;

      Prsd[15:0] <=  16'h0;

      LinkFail <=  1'b0;

    end

  else

    begin

      if(MdcEn_n)

        begin

          if(|ByteSelect)

            begin

              case (ByteSelect[3:0])  // synopsys parallel_case full_case

                4'h1 :    ShiftReg[7:0] <=  {2'b01, ~WriteOp, WriteOp, Fiad[4:1]};

                4'h2 :    ShiftReg[7:0] <=  {Fiad[0], Rgad[4:0], 2'b10};

                4'h4 :    ShiftReg[7:0] <=  CtrlData[15:8];

                4'h8 :    ShiftReg[7:0] <=  CtrlData[7:0];

              endcase

            end

          else

            begin

              ShiftReg[7:0] <=  {ShiftReg[6:0], Mdi};

              if(LatchByte[0])

                begin

                  Prsd[7:0] <=  {ShiftReg[6:0], Mdi};

                  if(Rgad == 5'h01)

                    LinkFail <=  ~ShiftReg[1];  // this is bit [2], because it is not shifted yet

                end

              else

                begin

                  if(LatchByte[1])

                    Prsd[15:8] <=  {ShiftReg[6:0], Mdi};

                end

            end

        end

    end

end

assign ShiftedBit = ShiftReg[7];

endmodule