git.zerfleddert.de Git - raggedstone/blob - ethernet/source/pci/pci_synchronizer_flop.v

   1 //===========================================================================
   2 // $Id: pci_synchronizer_flop.v,v 1.1 2007-03-20 17:50:56 sithglan Exp $
   3 //
   4 //////////////////////////////////////////////////////////////////////
   5 ////                                                              ////
   6 //// pci_synchronizer_flop                                        ////
   7 ////                                                              ////
   8 //// This file is part of the general opencores effort.           ////
   9 //// <http://www.opencores.org/cores/misc/>                       ////
  10 ////                                                              ////
  11 //// Module Description:                                          ////
  12 ////                                                              ////
  13 //// Make a rising-edge triggered flop with async reset with a    ////
  14 ////   distinguished name so that it can be replaced with a flop  ////
  15 ////   which does not make X's during simulation.                 ////
  16 ////                                                              ////
  17 //// This flop should be used instead of a regular flop for ALL   ////
  18 ////   cross-clock-domain flops.  Manually instantiating this     ////
  19 ////   flop for all signals which must NEVER go to 1'bX during    ////
  20 ////   simulation will make it possible for the user to           ////
  21 ////   substitute a simulation model which does NOT have setup    ////
  22 ////   and hold checks.                                           ////
  23 ////                                                              ////
  24 //// If a target device library has a component which is          ////
  25 ////   especially well suited to perform this function, it should ////
  26 ////   be instantiated by name in this file.  Otherwise, the      ////
  27 ////   behaviorial version of this module will be used.           ////
  28 ////                                                              ////
  29 //// To Do:                                                       ////
  30 //// Nothing                                                      ////
  31 ////                                                              ////
  32 //// Author(s):                                                   ////
  33 //// - anynomous                                                  ////
  34 ////                                                              ////
  35 //////////////////////////////////////////////////////////////////////
  36 ////                                                              ////
  37 //// Copyright (C) 2001 Authors and OPENCORES.ORG                 ////
  38 ////                                                              ////
  39 //// This source file may be used and distributed without         ////
  40 //// restriction provided that this copyright statement is not    ////
  41 //// removed from the file and that any derivative work contains  ////
  42 //// the original copyright notice and the associated disclaimer. ////
  43 ////                                                              ////
  44 //// This source file is free software; you can redistribute it   ////
  45 //// and/or modify it under the terms of the GNU Lesser General   ////
  46 //// Public License as published by the Free Software Foundation; ////
  47 //// either version 2.1 of the License, or (at your option) any   ////
  48 //// later version.                                               ////
  49 ////                                                              ////
  50 //// This source is distributed in the hope that it will be       ////
  51 //// useful, but WITHOUT ANY WARRANTY; without even the implied   ////
  52 //// warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR      ////
  53 //// PURPOSE. See the GNU Lesser General Public License for more  ////
  54 //// details.                                                     ////
  55 ////                                                              ////
  56 //// You should have received a copy of the GNU Lesser General    ////
  57 //// Public License along with this source; if not, download it   ////
  58 //// from <http://www.opencores.org/lgpl.shtml>                   ////
  59 ////                                                              ////
  60 //////////////////////////////////////////////////////////////////////
  61 //
  62 // CVS Revision History
  63 //
  64 // $Log: pci_synchronizer_flop.v,v $
  65 // Revision 1.1  2007-03-20 17:50:56  sithglan
  66 // add shit
  67 //
  68 // Revision 1.1  2003/08/14 13:08:58  simons
  69 // synchronizer_flop replaced with pci_synchronizer_flop, artisan ram instance updated.
  70 //
  71 //
  72
  73 // synopsys translate_off
  74 `include "timescale.v"
  75 // synopsys translate_on
  76
  77 // If the vendor has a flop which is particularly good at settling out of
  78 //   metastability, it should be used here.
  79 module pci_synchronizer_flop (
  80   data_in, clk_out, sync_data_out, async_reset
  81 );
  82 parameter               width = 1 ;
  83 parameter               reset_val = 0 ;
  84
  85   input   [width-1:0]   data_in;
  86   input                 clk_out;
  87   output  [width-1:0]   sync_data_out;
  88   input                 async_reset;
  89
  90   reg     [width-1:0]   sync_data_out;
  91
  92   always @(posedge clk_out or posedge async_reset)
  93   begin
  94     if (async_reset == 1'b1)
  95     begin
  96       sync_data_out <= reset_val;
  97     end
  98     else
  99     begin
 100 // In gate-level simulation, must only go to 1'bX if the input is 1'bX or 1'bZ.
 101 // This should NEVER go to 1'bX due to setup or hold violations.
 102       sync_data_out <= data_in;
 103     end
 104   end
 105 endmodule
 106