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--
-- Input filter
--
-- Author:   Sebastian Witt
-- Data:     06.03.2008
-- Version:  1.0
--
-- This code 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 code 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 library; if not, write to the
-- Free Software  Foundation, Inc., 59 Temple Place, Suite 330,
-- Boston, MA  02111-1307  USA
--
 
LIBRARY IEEE;
USE IEEE.std_logic_1164.all;
USE IEEE.numeric_std.all;
 
entity slib_input_filter is
    generic (
        SIZE        : natural := 4      -- Filter counter size
    );
    port (
        CLK         : in std_logic;     -- Clock
        RST         : in std_logic;     -- Reset
        CE          : in std_logic;     -- Clock enable
        D           : in std_logic;     -- Signal input
        Q           : out std_logic     -- Signal output
    );
end slib_input_filter;
 
architecture rtl of slib_input_filter is
    signal iCount : integer range 0 to SIZE;
begin
    IF_D: process (RST, CLK)
    begin
        if (RST  = '1') then
            iCount <= 0;
            Q      <= '0';
        elsif (CLK'event and CLK='1') then
            -- Input counter
            if (CE = '1' ) then
                if (D = '1' and iCount /= SIZE) then
                    iCount <= iCount + 1;
                elsif (D = '0' and iCount /= 0) then
                    iCount <= iCount - 1;
                end if;
            end if;
 
            -- Output
            if (iCount = SIZE) then
                Q <= '1';
            elsif (iCount = 0) then
                Q <= '0';
            end if;
        end if;
    end process;
 
end rtl;