
// Copyright (c) 2000-2012 Bluespec, Inc.

// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:

// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.

// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.
//
// $Revision$
// $Date$

`ifdef BSV_ASSIGNMENT_DELAY
`else
  `define BSV_ASSIGNMENT_DELAY
`endif

`ifdef BSV_POSITIVE_RESET
  `define BSV_RESET_VALUE 1'b1
  `define BSV_RESET_EDGE posedge
`else
  `define BSV_RESET_VALUE 1'b0
  `define BSV_RESET_EDGE negedge
`endif

`ifdef BSV_ASYNC_RESET
 `define BSV_ARESET_EDGE_META or `BSV_RESET_EDGE RST
`else
 `define BSV_ARESET_EDGE_META
`endif

`ifdef BSV_RESET_FIFO_HEAD
 `define BSV_ARESET_EDGE_HEAD `BSV_ARESET_EDGE_META
`else
 `define BSV_ARESET_EDGE_HEAD
`endif

// Depth 1 FIFO
// Allows simultaneous ENQ and DEQ (at the expense of potentially
// causing combinational loops).
module FIFOL1(CLK,
              RST,
              D_IN,
              ENQ,
              FULL_N,
              D_OUT,
              DEQ,
              EMPTY_N,
              CLR);

   parameter             width = 1;

   input                 CLK;
   input                 RST;

   input [width - 1 : 0] D_IN;
   input                 ENQ;
   input                 DEQ;
   input                 CLR ;

   output                FULL_N;
   output                 EMPTY_N;
   output [width - 1 : 0] D_OUT;



   reg                    empty_reg ;
   reg [width - 1 : 0]    D_OUT;

`ifdef BSV_NO_INITIAL_BLOCKS
`else // not BSV_NO_INITIAL_BLOCKS
   // synopsys translate_off
   initial
     begin
        D_OUT     <= `BSV_ASSIGNMENT_DELAY {((width + 1)/2) {2'b10}} ;
        empty_reg <= `BSV_ASSIGNMENT_DELAY 1'b0;
     end // initial begin
   // synopsys translate_on
`endif // BSV_NO_INITIAL_BLOCKS


   assign FULL_N = !empty_reg || DEQ;
   assign EMPTY_N = empty_reg ;

   always@(posedge CLK `BSV_ARESET_EDGE_META)
     begin
        if (RST == `BSV_RESET_VALUE)
           begin
             empty_reg <= `BSV_ASSIGNMENT_DELAY 1'b0;
           end
        else
           begin
              if (CLR)
                begin
                   empty_reg <= `BSV_ASSIGNMENT_DELAY 1'b0;
                end
              else if (ENQ)
                begin
                   empty_reg <= `BSV_ASSIGNMENT_DELAY 1'b1;
                end
              else if (DEQ)
                begin
                   empty_reg <= `BSV_ASSIGNMENT_DELAY 1'b0;
                end // if (DEQ)
           end // else: !if(RST == `BSV_RESET_VALUE)
     end // always@ (posedge CLK or `BSV_RESET_EDGE RST)

   always@(posedge CLK `BSV_ARESET_EDGE_HEAD)
     begin
`ifdef BSV_RESET_FIFO_HEAD
        if (RST == `BSV_RESET_VALUE)
          begin
             D_OUT <= `BSV_ASSIGNMENT_DELAY {width {1'b0}} ;
          end
        else
`endif
          begin
              if (ENQ)
                D_OUT     <= `BSV_ASSIGNMENT_DELAY D_IN;
           end // else: !if(RST == `BSV_RESET_VALUE)
     end // always@ (posedge CLK or `BSV_RESET_EDGE RST)

   // synopsys translate_off
   always@(posedge CLK)
     begin: error_checks
        reg deqerror, enqerror ;

        deqerror =  0;
        enqerror = 0;
        if ( ! empty_reg && DEQ )
          begin
             deqerror = 1 ;
             $display( "Warning: FIFOL1: %m -- Dequeuing from empty fifo" ) ;
          end
        if ( ! FULL_N && ENQ && ! DEQ)
          begin
             enqerror =  1 ;
             $display( "Warning: FIFOL1: %m -- Enqueuing to a full fifo" ) ;
          end
     end
   // synopsys translate_on

endmodule
