Subversion Repositories versatile_fifo

//////////////////////////////////////////////////////////////////////
////                                                              ////
////  Versatile counter                                           ////
////                                                              ////
////  Description                                                 ////
////  Versatile counter, a reconfigurable binary, gray or LFSR    ////
////  counter                                                     ////
////                                                              ////
////  To Do:                                                      ////
////   - add LFSR with more taps                                  ////
////                                                              ////
////  Author(s):                                                  ////
////      - Michael Unneback, unneback@opencores.org              ////
////        ORSoC AB                                              ////
////                                                              ////
//////////////////////////////////////////////////////////////////////
////                                                              ////
//// Copyright (C) 2009 Authors and OPENCORES.ORG                 ////
////                                                              ////
//// 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                     ////
////                                                              ////
//////////////////////////////////////////////////////////////////////
 
module versatile_fifo_async_cmp ( wptr, rptr, fifo_empty, fifo_full, wclk, rclk, rst );
 
   parameter ADDR_WIDTH = 4;   
   parameter N = ADDR_WIDTH-1;
 
   parameter Q1 = 2'b00;
   parameter Q2 = 2'b01;
   parameter Q3 = 2'b11;
   parameter Q4 = 2'b10;
 
   parameter going_empty = 1'b0;
   parameter going_full  = 1'b1;
 
   input [N:0]  wptr, rptr;   
   output reg	fifo_empty;
   output       fifo_full;
   input 	wclk, rclk, rst;   
 
   reg 	direction, direction_set, direction_clr;
 
   wire async_empty, async_full;
   wire fifo_full2;
   reg  fifo_empty2;   
 
   // direction_set
   always @ (wptr[N:N-1] or rptr[N:N-1])
     case ({wptr[N:N-1],rptr[N:N-1]})
       {Q1,Q2} : direction_set <= 1'b1;
       {Q2,Q3} : direction_set <= 1'b1;
       {Q3,Q4} : direction_set <= 1'b1;
       {Q4,Q1} : direction_set <= 1'b1;
       default : direction_set <= 1'b0;
     endcase
 
   // direction_clear
   always @ (wptr[N:N-1] or rptr[N:N-1] or rst)
     if (rst)
       direction_clr <= 1'b1;
     else
       case ({wptr[N:N-1],rptr[N:N-1]})
	 {Q2,Q1} : direction_clr <= 1'b1;
	 {Q3,Q2} : direction_clr <= 1'b1;
	 {Q4,Q3} : direction_clr <= 1'b1;
	 {Q1,Q4} : direction_clr <= 1'b1;
	 default : direction_clr <= 1'b0;
       endcase
 
`ifndef GENERATE_DIRECTION_AS_LATCH
    dff_sr dff_sr_dir( .aclr(direction_clr), .aset(direction_set), .clock(1'b1), .data(1'b1), .q(direction));
`endif
 
`ifdef GENERATE_DIRECTION_AS_LATCH
   always @ (posedge direction_set or posedge direction_clr)
     if (direction_clr)
       direction <= going_empty;
     else
       direction <= going_full;
`endif
 
   assign async_empty = (wptr == rptr) && (direction==going_empty);
   assign async_full  = (wptr == rptr) && (direction==going_full);
 
    dff_sr dff_sr_empty0( .aclr(rst), .aset(async_full), .clock(wclk), .data(async_full), .q(fifo_full2));
    dff_sr dff_sr_empty1( .aclr(rst), .aset(async_full), .clock(wclk), .data(fifo_full2), .q(fifo_full));
 
/*
   always @ (posedge wclk or posedge rst or posedge async_full)
     if (rst)
       {fifo_full, fifo_full2} <= 2'b00;
     else if (async_full)
       {fifo_full, fifo_full2} <= 2'b11;
     else
       {fifo_full, fifo_full2} <= {fifo_full2, async_full};
*/
   always @ (posedge rclk or posedge async_empty)
     if (async_empty)
       {fifo_empty, fifo_empty2} <= 2'b11;
     else
       {fifo_empty,fifo_empty2} <= {fifo_empty2,async_empty};   
 
endmodule // async_comp