Subversion Repositories openrisc_2011-10-31

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

////                                                              ////

////  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 $

//

`include "timescale.v"

module uart_sync_flops

(

  // internal signals

  rst_i,

  clk_i,

  stage1_rst_i,

  stage1_clk_en_i,

  async_dat_i,

  sync_dat_o

);

parameter Tp            = 1;

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 <= #Tp {width{init_value}};

    else

        flop_0 <= #Tp async_dat_i;

end

// second stage

always @ (posedge clk_i or posedge rst_i)

begin

    if (rst_i)

        sync_dat_o <= #Tp {width{init_value}};

    else if (stage1_rst_i)

        sync_dat_o <= #Tp {width{init_value}};

    else if (stage1_clk_en_i)

        sync_dat_o <= #Tp flop_0;

end

endmodule