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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