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

////                                                              ////

////  uart_fifo.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 FIFO                                     ////

////                                                              ////

////  Known problems (limits):                                    ////

////  Note that the same FIFO is used for both transmission  and  ////

////  reception but the error bit generation is ignored in tx.    ////

////                                                              ////

////  To Do:                                                      ////

////  Nothing.                                                    ////

////                                                              ////

////  Author(s):                                                  ////

////      - gorban@opencores.org                                  ////

////      - Jacob Gorban                                          ////

////      - Igor Mohor (igorm@opencores.org)                      ////

////                                                              ////

////  Created:        2001/05/12                                  ////

////  Last Updated:   2001/05/17                                  ////

////                  (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 $

// Revision 1.17  2002/01/13 20:13:07  gorban

// Removed confusing comment

//

// Revision 1.16  2001/12/20 13:25:46  mohor

// rx push changed to be only one cycle wide.

//

// Revision 1.15  2001/12/18 09:01:07  mohor

// Bug that was entered in the last update fixed (rx state machine).

//

// Revision 1.14  2001/12/17 14:46:48  mohor

// overrun signal was moved to separate block because many sequential lsr

// reads were preventing data from being written to rx fifo.

// underrun signal was not used and was removed from the project.

//

// Revision 1.13  2001/11/26 21:38:54  gorban

// Lots of fixes:

// Break condition wasn't handled correctly at all.

// LSR bits could lose their values.

// LSR value after reset was wrong.

// Timing of THRE interrupt signal corrected.

// LSR bit 0 timing corrected.

//

// Revision 1.12  2001/11/08 14:54:23  mohor

// Comments in Slovene language deleted, few small fixes for better work of

// old tools. IRQs need to be fix.

//

// Revision 1.11  2001/11/07 17:51:52  gorban

// Heavily rewritten interrupt and LSR subsystems.

// Many bugs hopefully squashed.

//

// Revision 1.10  2001/10/20 09:58:40  gorban

// Small synopsis fixes

//

// Revision 1.9  2001/08/24 21:01:12  mohor

// Things connected to parity changed.

// Clock devider changed.

//

// Revision 1.8  2001/08/24 08:48:10  mohor

// FIFO was not cleared after the data was read bug fixed.

//

// Revision 1.7  2001/08/23 16:05:05  mohor

// Stop bit bug fixed.

// Parity bug fixed.

// WISHBONE read cycle bug fixed,

// OE indicator (Overrun Error) bug fixed.

// PE indicator (Parity Error) bug fixed.

// Register read bug fixed.

//

// Revision 1.3  2001/05/31 20:08:01  gorban

// FIFO changes and other corrections.

//

// Revision 1.3  2001/05/27 17:37:48  gorban

// Fixed many bugs. Updated spec. Changed FIFO files structure. See CHANGES.txt file.

//

// Revision 1.2  2001/05/17 18:34:18  gorban

// First 'stable' release. Should be sythesizable now. Also added new header.

//

// Revision 1.0  2001-05-17 21:27:12+02  jacob

// Initial revision

//

//

// synopsys translate_off

`include "timescale.v"

// synopsys translate_on

`include "uart_defines.v"

module uart_fifo (clk,

        wb_rst_i, data_in, data_out,

// Control signals

        push, // push strobe, active high

        pop,   // pop strobe, active high

// status signals

        overrun,

        count,

        error_bit,

        fifo_reset,

        reset_status

        );

// FIFO parameters

parameter fifo_width = `UART_FIFO_WIDTH;

parameter fifo_depth = `UART_FIFO_DEPTH;

parameter fifo_pointer_w = `UART_FIFO_POINTER_W;

parameter fifo_counter_w = `UART_FIFO_COUNTER_W;

input                           clk;

input                           wb_rst_i;

input                           push;

input                           pop;

input   [fifo_width-1:0] data_in;

input                           fifo_reset;

input       reset_status;

output  [fifo_width-1:0] data_out;

output                          overrun;

output  [fifo_counter_w-1:0]     count;

output                          error_bit;

wire    [fifo_width-1:0] data_out;

// FIFO itself

reg     [fifo_width-1:0] fifo[fifo_depth-1:0];

// FIFO pointers

reg     [fifo_pointer_w-1:0]     top;

reg     [fifo_pointer_w-1:0]     bottom;

reg     [fifo_counter_w-1:0]     count;

reg                             overrun;

wire [fifo_pointer_w-1:0] top_plus_1 = top + 1'b1;

always @(posedge clk or posedge wb_rst_i) // synchronous FIFO

begin

        if (wb_rst_i)

        begin

                top             <= #1 0;

                bottom          <= #1 1'b0;

                count           <= #1 0;

                fifo[0]          <= #1 0;

                fifo[1]         <= #1 0;

                fifo[2]         <= #1 0;

                fifo[3]         <= #1 0;

                fifo[4]         <= #1 0;

                fifo[5]         <= #1 0;

                fifo[6]         <= #1 0;

                fifo[7]         <= #1 0;

                fifo[8]         <= #1 0;

                fifo[9]         <= #1 0;

                fifo[10]        <= #1 0;

                fifo[11]        <= #1 0;

                fifo[12]        <= #1 0;

                fifo[13]        <= #1 0;

                fifo[14]        <= #1 0;

                fifo[15]        <= #1 0;

        end

        else

        if (fifo_reset) begin

                top             <= #1 0;

                bottom          <= #1 1'b0;

                count           <= #1 0;

        end

  else

        begin

                case ({push, pop})

                2'b10 : if (count<fifo_depth)  // overrun condition

                        begin

                                top       <= #1 top_plus_1;

                                fifo[top] <= #1 data_in;

                                count     <= #1 count + 1'b1;

                        end

                2'b01 : if(count>0)

                        begin

        fifo[bottom] <= #1 0;

                                bottom   <= #1 bottom + 1'b1;

                                count    <= #1 count - 1'b1;

                        end

                2'b11 : begin

        fifo[bottom] <= #1 0;

                                bottom   <= #1 bottom + 1'b1;

                                top       <= #1 top_plus_1;

                                fifo[top] <= #1 data_in;

                        end

    default: ;

                endcase

        end

end   // always

always @(posedge clk or posedge wb_rst_i) // synchronous FIFO

begin

  if (wb_rst_i)

    overrun   <= #1 1'b0;

  else

  if(fifo_reset | reset_status)

    overrun   <= #1 1'b0;

  else

  if(push & (count==fifo_depth))

    overrun   <= #1 1'b1;

end   // always

assign data_out = fifo[bottom];

// Additional logic for detection of error conditions (parity and framing) inside the FIFO

// for the Line Status Register bit 7

wire    [fifo_width-1:0] word0 = fifo[0];

wire    [fifo_width-1:0] word1 = fifo[1];

wire    [fifo_width-1:0] word2 = fifo[2];

wire    [fifo_width-1:0] word3 = fifo[3];

wire    [fifo_width-1:0] word4 = fifo[4];

wire    [fifo_width-1:0] word5 = fifo[5];

wire    [fifo_width-1:0] word6 = fifo[6];

wire    [fifo_width-1:0] word7 = fifo[7];

wire    [fifo_width-1:0] word8 = fifo[8];

wire    [fifo_width-1:0] word9 = fifo[9];

wire    [fifo_width-1:0] word10 = fifo[10];

wire    [fifo_width-1:0] word11 = fifo[11];

wire    [fifo_width-1:0] word12 = fifo[12];

wire    [fifo_width-1:0] word13 = fifo[13];

wire    [fifo_width-1:0] word14 = fifo[14];

wire    [fifo_width-1:0] word15 = fifo[15];

// a 1 is returned if any of the error bits in the fifo is 1

assign  error_bit = |(word0[2:0]  | word1[2:0]  | word2[2:0]  | word3[2:0]  |

                              word4[2:0]  | word5[2:0]  | word6[2:0]  | word7[2:0]  |

                              word8[2:0]  | word9[2:0]  | word10[2:0] | word11[2:0] |

                              word12[2:0] | word13[2:0] | word14[2:0] | word15[2:0] );

endmodule