verilog/rtl/uart_sync_flops.v

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