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

////                                                              ////

////  spi_slave_model.v                                           ////

////                                                              ////

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

////  http://www.opencores.org/projects/spi/                      ////

////                                                              ////

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

////      - Simon Srot (simons@opencores.org)                     ////

////                                                              ////

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

////  file.                                                       ////

////                                                              ////

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

////                                                              ////

//// Copyright (C) 2002 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. ////

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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.                                                     ////

////                                                              ////

//// 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                     ////

////                                                              ////

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

`include "timescale.v"

module spi_slave_model (rst, ss, sclk, mosi, miso);

  input         rst;            // reset

  input         ss;             // slave select

  input         sclk;           // serial clock

  input         mosi;           // master out slave in

  output        miso;           // master in slave out

  reg           miso;

  reg           rx_negedge;     // slave receiving on negedge

  reg           tx_negedge;     // slave transmiting on negedge

  reg    [31:0] data;           // data register

  parameter     Tp = 1;

  always @(posedge(sclk && !rx_negedge) or negedge(sclk && rx_negedge) or rst)

  begin

    if (rst)

      data <= #Tp 32'b0;

    else if (!ss)

      data <= #Tp {data[30:0], mosi};

  end

  always @(posedge(sclk && !tx_negedge) or negedge(sclk && tx_negedge))

  begin

    miso <= #Tp data[31];

  end

endmodule