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//////////////////////////////////////////////////////////////////////
////                                                              ////
////  eth_fifo.v                                                  ////
////                                                              ////
////  This file is part of the Ethernet IP core project           ////
////  http://www.opencores.org/projects/ethmac/                   ////
////                                                              ////
////  Author(s):                                                  ////
////      - Igor Mohor (igorM@opencores.org)                      ////
////                                                              ////
////  All additional information is avaliable in the Readme.txt   ////
////  file.                                                       ////
////                                                              ////
//////////////////////////////////////////////////////////////////////
////                                                              ////
//// Copyright (C) 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 1.5  2005/04/26   14:55           btltz
// Major change is on assignment of "cnt". Add "read_alw"	and "write_alw".
// minors: expand depth for use. change to asychronous read. output comment. Use Xilinx block dpRAM template style. not use clear.
//
// Revision 1.4  2005/02/21 12:48:07  igorm
// Warning fixes.
//
// Revision 1.3  2002/04/22 13:45:52  mohor
// Generic ram or Xilinx ram can be used in fifo (selectable by setting
// ETH_FIFO_XILINX in eth_defines.v).
//
// Revision 1.2  2002/03/25 13:33:04  mohor
// When clear and read/write are active at the same time, cnt and pointers are
// set to 1.
//
// Revision 1.1  2002/02/05 16:44:39  mohor
// Both rx and tx part are finished. Tested with wb_clk_i between 10 and 200
// MHz. Statuses, overrun, control frame transmission and reception still  need
// to be fixed.
//
//
 
 
//`include "timescale.v"
`define XIL_BRAM	    //Use Xilinx block RAM
//`define XIL_DISRAM	 //Use Xilinx distributed RAM
`define reset   1     //WISHBONE style reset
`define SIMULATION
 
module eth_fifo (data_in, data_out, clk, reset, write, read, almost_full, full, almost_empty, empty, cnt);
 
parameter DATA_WIDTH    = 32;	
`ifdef SIMULATION 
parameter DEPTH         = 16;	 
`else
parameter DEPTH         = 64;
`endif	
parameter CNT_WIDTH     = (DEPTH < 8) ?  3 :
                          ((DEPTH < 16) ?  4 :
									 ((DEPTH < 32) ?  5 :
									  ((DEPTH < 64) ?  6 :
									   ((DEPTH < 128) ?  7 :
										 ((DEPTH < 256) ?  8 :
										  ((DEPTH < 512) ?   9 :
										   ((DEPTH < 1024) ?  10 :
											 ((DEPTH < 2048) ?   11 :
											  ((DEPTH < 4096) ?    12 : 'bx   // Add more ?
											   )))))))));
 
parameter WP_WIDTH = ( DEPTH==8 || DEPTH==16 || DEPTH==32 || DEPTH==64 || DEPTH==128 ||
                       DEPTH==256 || DEPTH==512 || DEPTH==1024 || DEPTH==2048 || DEPTH==4096 
							 )	  ?   (CNT_WIDTH-1)   :   CNT_WIDTH;
 
parameter RP_WIDTH = WP_WIDTH;
 
//parameter Tp            = 1;
 
input                     clk;
input                     reset;
input                     write;
input                     read;
// input                     clear;
input   [DATA_WIDTH-1:0]  data_in;
 
output  [DATA_WIDTH-1:0]  data_out;
output                    almost_full;
output                    full;
output                    almost_empty;
output                    empty;
output  [CNT_WIDTH-1:0]   cnt;
 
`ifdef ETH_FIFO_XILINX
`else
  `ifdef ETH_ALTERA_ALTSYNCRAM
  `else
    reg     [DATA_WIDTH-1:0]  dpRam  [0:DEPTH-1];
   // reg     [DATA_WIDTH-1:0]  data_out;
  `endif
`endif
 
reg     [CNT_WIDTH-1:0]   cnt;	       // eg: 0-1--16			// eg: 0-1--24
reg     [RP_WIDTH-1:0]    read_pointer; // eg: 0-15				// eg: 0-23
reg     [WP_WIDTH-1:0]    write_pointer;// eg: 0-15				// eg: 0-23
 
wire read_alw = read && !empty;
wire write_alw = write &&  !full;  
 
always @ (posedge clk or posedge reset)
begin
  if(reset)
    cnt <= 0;
  else if(read ^ write)
       begin
		 if( read_alw )
		  cnt <= cnt - 1'b1;
       else if(write_alw) 
        cnt <= cnt + 1'b1;
		 end
  else if(write && empty)  // (read && write) when empty
        cnt<= cnt + 1'b1; 
end
 
always @ (posedge clk or posedge reset)
begin
  if(reset)
    read_pointer <= 0;
  else
  if(read_alw) //      
    begin
	 if( read_pointer==DEPTH-1 )    // to support arbitrary depth
	 read_pointer <= 0;
	 else
    read_pointer <= read_pointer + 1'b1;
	 end
end
 
always @ (posedge clk or posedge reset)
begin
  if(reset)
    write_pointer <= 1;		       // ignor bit0 at the very beginning
  else
  if(write_alw )
    begin
    if( write_pointer==DEPTH-1 )	 // to support arbitrary depth
	 write_pointer <= 0;
	 else
	 write_pointer <= write_pointer + 1'b1;
	 end
end
 
// UNregistered outputs. assert while clk after low->high + gate latency
assign empty = ~(|cnt);			     
assign almost_empty = cnt == 1;		         //pulse output
assign full = ( cnt == DEPTH-1);		         // ignor 1 word to make right wr/rd on dprem
//assign almost_full  = &cnt[CNT_WIDTH-2:0]; //pulse output
assign almost_full = (cnt == DEPTH-2);
 
 
 
`ifdef ETH_FIFO_XILINX
  xilinx_dist_ram_16x32 fifo
  ( .data_out(data_out), 
    .we(write & ~full),
    .data_in(data_in),
    .read_address( clear ? {CNT_WIDTH-1{1'b0}} : read_pointer),
    .write_address(clear ? {CNT_WIDTH-1{1'b0}} : write_pointer),
    .wclk(clk)
  );
`else   // !ETH_FIFO_XILINX
`ifdef ETH_ALTERA_ALTSYNCRAM
  altera_dpram_16x32	altera_dpram_16x32_inst
  (
  	.data             (data_in),
  	.wren              (write & ~full),
  	.wraddress        (clear ? {CNT_WIDTH-1{1'b0}} : write_pointer),
  	.rdaddress        (clear ? {CNT_WIDTH-1{1'b0}} : read_pointer ),
  	.clock            (clk),
  	.q                (data_out)
  );  //exemplar attribute altera_dpram_16x32_inst NOOPT TRUE
`else   // !ETH_ALTERA_ALTSYNCRAM
 
`ifdef XIL_BRAM
reg [RP_WIDTH-1:0]  rp1;
 always @ (posedge clk) begin 
  if(write & ~full)
      dpRam[write_pointer] <= data_in;
  rp1 <= read_pointer;
  end	   
 
assign   data_out = dpRam[rp1];   // if use block RAM, 1 clock data output latency 
`else 
  always @ (posedge clk) begin 
  if(write & ~full)
      dpRam[write_pointer] <= data_in;	 
  end	    
  assign   data_out = dpRam[read_pointer]; 
`endif
 
`endif  // !ETH_ALTERA_ALTSYNCRAM
`endif  // !ETH_FIFO_XILINX
 
 
endmodule
 
`undef reset
`undef XIL_BRAM
`undef SIMULATION