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microwatt/uart16550/uart_sync_flops.v

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//////////////////////////////////////////////////////////////////////
//// ////
//// uart_sync_flops.v ////
//// ////
//// ////
//// This file is part of the "UART 16550 compatible" project ////
//// http://www.opencores.org/cores/uart16550/ ////
//// ////
//// Documentation related to this project: ////
//// - http://www.opencores.org/cores/uart16550/ ////
//// ////
//// Projects compatibility: ////
//// - WISHBONE ////
//// RS232 Protocol ////
//// 16550D uart (mostly supported) ////
//// ////
//// Overview (main Features): ////
//// UART core receiver logic ////
//// ////
//// Known problems (limits): ////
//// None known ////
//// ////
//// To Do: ////
//// Thourough testing. ////
//// ////
//// Author(s): ////
//// - Andrej Erzen (andreje@flextronics.si) ////
//// - Tadej Markovic (tadejm@flextronics.si) ////
//// ////
//// Created: 2004/05/20 ////
//// Last Updated: 2004/05/20 ////
//// (See log for the revision history) ////
//// ////
//// ////
//////////////////////////////////////////////////////////////////////
//// ////
//// Copyright (C) 2000, 2001 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. ////
//// ////
//// 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 $
//
module uart_sync_flops
(
// internal signals
rst_i,
clk_i,
stage1_rst_i,
stage1_clk_en_i,
async_dat_i,
sync_dat_o
);
parameter width = 1;
parameter init_value = 1'b0;
input rst_i; // reset input
input clk_i; // clock input
input stage1_rst_i; // synchronous reset for stage 1 FF
input stage1_clk_en_i; // synchronous clock enable for stage 1 FF
input [width-1:0] async_dat_i; // asynchronous data input
output [width-1:0] sync_dat_o; // synchronous data output
//
// Interal signal declarations
//
reg [width-1:0] sync_dat_o;
reg [width-1:0] flop_0;
// first stage
always @ (posedge clk_i or posedge rst_i)
begin
if (rst_i)
flop_0 <= {width{init_value}};
else
flop_0 <= async_dat_i;
end
// second stage
always @ (posedge clk_i or posedge rst_i)
begin
if (rst_i)
sync_dat_o <= {width{init_value}};
else if (stage1_rst_i)
sync_dat_o <= {width{init_value}};
else if (stage1_clk_en_i)
sync_dat_o <= flop_0;
end
endmodule