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//////////////////////////////////////////////////////////////////////
////                                                              ////
////  uart_rfifo.v (Modified from 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                                     ////
////                                                              ////
////  To Do:                                                      ////
////  Nothing.                                                    ////
////                                                              ////
////  Author(s):                                                  ////
////      - gorban@opencores.org                                  ////
////      - Jacob Gorban                                          ////
////      - Igor Mohor (igorm@opencores.org)                      ////
////                                                              ////
////  Created:        2001/05/12                                  ////
////  Last Updated:   2002/07/22                                  ////
////                  (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 1.3  2003/06/11 16:37:47  gorban
// This fixes errors in some cases when data is being read and put to the FIFO at the same time. Patch is submitted by Scott Furman. Update is very recommended.
//
// Revision 1.2  2002/07/29 21:16:18  gorban
// The uart_defines.v file is included again in sources.
//
// Revision 1.1  2002/07/22 23:02:23  gorban
// Bug Fixes:
//  * Possible loss of sync and bad reception of stop bit on slow baud rates fixed.
//   Problem reported by Kenny.Tung.
//  * Bad (or lack of ) loopback handling fixed. Reported by Cherry Withers.
//
// Improvements:
//  * Made FIFO's as general inferrable memory where possible.
//  So on FPGA they should be inferred as RAM (Distributed RAM on Xilinx).
//  This saves about 1/3 of the Slice count and reduces P&R and synthesis times.
//
//
// 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
//
//



module `VARIANT`RFIFO  (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;
wire [7:0] data8_out;
// flags FIFO
reg     [2:0]   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 + 4'h1;



`VARIANT`RAMINFR 
  #( .addr_width  ( fifo_pointer_w ),
     .data_width  ( 8              ),
     .depth       ( fifo_depth     )
     ) rfifo (
             .clk(clk), 
             .we(push), 
             .a(top), 
             .dpra(bottom), 
             .di(data_in[fifo_width-1:fifo_width-8]), 
             .dpo(data8_out)
                ); 

always @(posedge clk ) // synchronous FIFO
begin
        if (wb_rst_i)
        begin
                top             <=  0;
                bottom          <=  0;     
                count           <=  0;
                fifo[0] <=  0;
                fifo[1] <=  0;
                fifo[2] <=  0;
                fifo[3] <=  0;
                fifo[4] <=  0;
                fifo[5] <=  0;
                fifo[6] <=  0;
                fifo[7] <=  0;
                fifo[8] <=  0;
                fifo[9] <=  0;
                fifo[10] <=  0;
                fifo[11] <=  0;
                fifo[12] <=  0;
                fifo[13] <=  0;
                fifo[14] <=  0;
                fifo[15] <=  0;
        end
        else
        if (fifo_reset) begin
                top             <=  0;
                bottom          <=  0;
                count           <=  0;
                fifo[0] <=  0;
                fifo[1] <=  0;
                fifo[2] <=  0;
                fifo[3] <=  0;
                fifo[4] <=  0;
                fifo[5] <=  0;
                fifo[6] <=  0;
                fifo[7] <=  0;
                fifo[8] <=  0;
                fifo[9] <=  0;
                fifo[10] <=  0;
                fifo[11] <=  0;
                fifo[12] <=  0;
                fifo[13] <=  0;
                fifo[14] <=  0;
                fifo[15] <=  0;
        end
  else
        begin
                case ({push, pop})
                2'b10 : if (count<fifo_depth)  // overrun condition
                        begin
                                top       <=  top_plus_1;
                                fifo[top] <=  data_in[2:0];
                                count     <=  count + 5'd1;
                        end
                2'b01 : if(count>0)
                        begin
        fifo[bottom] <=  0;
                                bottom   <=  bottom + 4'd1;
                                count    <=  count - 5'd1;
                        end
                2'b11 : begin
                                bottom   <=  bottom + 4'd1;
                                top       <=  top_plus_1;
                                fifo[top] <=  data_in[2:0];
                        end
    default: ;
                endcase
        end
end   // always

always @(posedge clk ) // synchronous FIFO
begin
  if (wb_rst_i)
    overrun   <=  1'b0;
  else
  if(fifo_reset | reset_status) 
    overrun   <=  1'b0;
  else
  if(push & ~pop & (count==fifo_depth))
    overrun   <=  1'b1;
end   // always


// please note though that data_out is only valid one clock after pop signal
assign data_out = {data8_out,fifo[bottom]};

// Additional logic for detection of error conditions (parity and framing) inside the FIFO
// for the Line Status Register bit 7

wire    [2:0]   word0 = fifo[0];
wire    [2:0]   word1 = fifo[1];
wire    [2:0]   word2 = fifo[2];
wire    [2:0]   word3 = fifo[3];
wire    [2:0]   word4 = fifo[4];
wire    [2:0]   word5 = fifo[5];
wire    [2:0]   word6 = fifo[6];
wire    [2:0]   word7 = fifo[7];

wire    [2:0]   word8 = fifo[8];
wire    [2:0]   word9 = fifo[9];
wire    [2:0]   word10 = fifo[10];
wire    [2:0]   word11 = fifo[11];
wire    [2:0]   word12 = fifo[12];
wire    [2:0]   word13 = fifo[13];
wire    [2:0]   word14 = fifo[14];
wire    [2:0]   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