Subversion Repositories common

//===========================================================================

// $Id: synchronizer_flop.v,v 1.4 2001-09-03 13:18:30 bbeaver Exp $

//

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

////                                                              ////

//// synchronizer_flop                                            ////

////                                                              ////

//// This file is part of the general opencores effort.           ////

//// <http://www.opencores.org/cores/misc/>                       ////

////                                                              ////

//// Module Description:                                          ////

////                                                              ////

//// Make a rising-edge triggered flop with async reset with a    ////

////   distinguished name so that it can be replaced with a flop  ////

////   which does not make X's during simulation.                 ////

////                                                              ////

//// This flop should be used instead of a regular flop for ALL   ////

////   cross-clock-domain flops.  Manually instantiating this     ////

////   flop for all signals which must NEVER go to 1'bX during    ////

////   simulation will make it possible for the user to           ////

////   substitute a simulation model which does NOT have setup    ////

////   and hold checks.                                           ////

////                                                              ////

//// If a target device library has a component which is          ////

////   especially well suited to perform this function, it should ////

////   be instantiated by name in this file.  Otherwise, the      ////

////   behaviorial version of this module will be used.           ////

////                                                              ////

//// To Do:                                                       ////

//// Nothing                                                      ////

////                                                              ////

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

//// - anynomous                                                  ////

////                                                              ////

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

////                                                              ////

//// Copyright (C) 2001 Authors and OPENCORES.ORG                 ////

////                                                              ////

//// 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>                   ////

////                                                              ////

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

//

// CVS Revision History

//

// $Log: not supported by cvs2svn $

// Revision 1.1  2001/09/03 11:16:00  Blue Beaver

// no message

//

// Revision 1.1.1.1  2001/09/03 10:24:58  bbeaver

// no message

//

// Revision 1.1  2001/09/02 11:32:03  Blue Beaver

// no message

//

//

`timescale 1ns/1ps

// If the vendor has a flop which is particularly good at settling out of

//   metastability, it should be used here.

module synchronizer_flop (

  data_in, clk_out, sync_data_out, async_reset

);

  input   data_in;

  input   clk_out;

  output  sync_data_out;

  input   async_reset;

  reg     sync_data_out;

  always @(posedge clk_out or posedge async_reset)

  begin

    if (async_reset == 1'b1)

    begin

      sync_data_out <= 1'b0;

    end

    else

    begin

// In gate-level simulation, must only go to 1'bX if the input is 1'bX or 1'bZ.

// This should NEVER go to 1'bX due to setup or hold violations.

      sync_data_out <= data_in;

    end

  end

endmodule