Subversion Repositories openrisc_2011-10-31

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

////                                                              ////

////  spi_clgen.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                                   ////

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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. ////

////                                                              ////

//// 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                     ////

////                                                              ////

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

`include "spi_defines.v"

`include "timescale.v"

module spi_flash_clgen (clk_in, rst, go, enable, last_clk, clk_out, pos_edge, neg_edge);

   parameter divider_len = 2;

   parameter divider = 1;

   parameter Tp = 1;

   input                            clk_in;   // input clock (system clock)

   input                            rst;      // reset

   input                            enable;   // clock enable

   input                            go;       // start transfer

   input                            last_clk; // last clock

   //input [spi_divider_len-1:0]     divider;  // clock divider (output clock is divided by this value)

   output                           clk_out;  // output clock

   output                           pos_edge; // pulse marking positive edge of clk_out

   output                           neg_edge; // pulse marking negative edge of clk_out

   reg                              clk_out;

   reg                              pos_edge;

   reg                              neg_edge;

   reg [divider_len-1:0]             cnt;      // clock counter 

   wire                             cnt_zero; // conter is equal to zero

   wire                             cnt_one;  // conter is equal to one

   assign cnt_zero = cnt == {divider_len{1'b0}};

   assign cnt_one  = cnt == {{divider_len-1{1'b0}}, 1'b1};

   // Counter counts half period

   always @(posedge clk_in or posedge rst)

     begin

        if(rst)

          cnt <= #Tp {divider_len{1'b1}};

        else

          begin

             if(!enable || cnt_zero)

               cnt <= #Tp divider;

             else

               cnt <= #Tp cnt - {{divider_len-1{1'b0}}, 1'b1};

          end

     end

   // clk_out is asserted every other half period

   always @(posedge clk_in or posedge rst)

     begin

        if(rst)

          clk_out <= #Tp 1'b0;

        else

          clk_out <= #Tp (enable && cnt_zero && (!last_clk || clk_out)) ? ~clk_out : clk_out;

     end

   // Pos and neg edge signals

   always @(posedge clk_in or posedge rst)

     begin

        if(rst)

          begin

             pos_edge  <= #Tp 1'b0;

             neg_edge  <= #Tp 1'b0;

          end

        else

          begin

             pos_edge  <= #Tp (enable && !clk_out && cnt_one) || (!(|divider) && clk_out) || (!(|divider) && go && !enable);

             neg_edge  <= #Tp (enable && clk_out && cnt_one) || (!(|divider) && !clk_out && enable);

          end

     end

endmodule