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[/] [pci/] [tags/] [asyst_3/] [rtl/] [verilog/] [pci_synchronizer_flop.v] - Rev 134
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//=========================================================================== // $Id: pci_synchronizer_flop.v,v 1.1 2003-08-14 13:08:58 simons Exp $ // ////////////////////////////////////////////////////////////////////// //// //// //// pci_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 $ // // synopsys translate_off `include "timescale.v" // synopsys translate_on // If the vendor has a flop which is particularly good at settling out of // metastability, it should be used here. module pci_synchronizer_flop ( data_in, clk_out, sync_data_out, async_reset ); parameter width = 1 ; parameter reset_val = 0 ; input [width-1:0] data_in; input clk_out; output [width-1:0] sync_data_out; input async_reset; reg [width-1:0] sync_data_out; always @(posedge clk_out or posedge async_reset) begin if (async_reset == 1'b1) begin sync_data_out <= reset_val; 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
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