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--

-- Counter

--

-- Author:   Sebastian Witt

-- Date:     27.01.2008

-- Version:  1.2

--

-- 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;

-- Counter

entity slib_counter is

    generic (

        WIDTH       : natural := 4       -- Counter width

    );

    port (

        CLK         : in std_logic;      -- Clock

        RST         : in std_logic;      -- Reset

        CLEAR       : in std_logic;      -- Clear counter register

        LOAD        : in std_logic;      -- Load counter register

        ENABLE      : in std_logic;      -- Enable count operation

        DOWN        : in std_logic;      -- Count direction down

        D           : in std_logic_vector(WIDTH-1 downto 0);    -- Load counter register input

        Q           : out std_logic_vector(WIDTH-1 downto 0);   -- Shift register output

        OVERFLOW    : out std_logic      -- Counter overflow

    );

end slib_counter;

architecture rtl of slib_counter is

    signal iCounter : unsigned(WIDTH downto 0);         -- Counter register

begin

    -- Counter process

    COUNT_SHIFT: process (RST, CLK)

    begin

        if (RST = '1') then

            iCounter <= (others => '0');                -- Reset counter register

        elsif (CLK'event and CLK='1') then

            if (CLEAR = '1') then

                iCounter <= (others => '0');            -- Clear counter register

            elsif (LOAD = '1') then                     -- Load counter register

                iCounter <= unsigned('0' & D);

            elsif (ENABLE = '1') then                   -- Enable counter

                if (DOWN = '0') then                    -- Count up

                    iCounter <= iCounter + 1;

                else                                    -- Count down

                    iCounter <= iCounter - 1;

                end if;

            end if;

            if (iCounter(WIDTH) = '1') then             -- Clear overflow

                iCounter(WIDTH) <= '0';

            end if;

        end if;

    end process;

    -- Output ports

    Q        <= std_logic_vector(iCounter(WIDTH-1 downto 0));

    OVERFLOW <= iCounter(WIDTH);

end rtl;