library ieee;
use ieee.std_logic_1164.all;
use ieee.numeric_std.all;

------------------------------------------------------------
-- Полный одноразрядный сумматор
------------------------------------------------------------
entity full_adder is
    port(
        a    : in  std_logic;
        b    : in  std_logic;
        cin  : in  std_logic;
        s    : out std_logic;
        cout : out std_logic
    );
end full_adder;

architecture beh of full_adder is
begin
    s    <= a xor b xor cin;
    cout <= (a and b) or (a and cin) or (b and cin);
end beh;

------------------------------------------------------------
-- Верхний модуль
------------------------------------------------------------
entity sum4_de2 is
    port(
        SW   : in  std_logic_vector(7 downto 0);
        HEX0 : out std_logic_vector(6 downto 0);
        HEX1 : out std_logic_vector(6 downto 0)
    );
end sum4_de2;

architecture beh of sum4_de2 is

    component full_adder
        port(
            a    : in  std_logic;
            b    : in  std_logic;
            cin  : in  std_logic;
            s    : out std_logic;
            cout : out std_logic
        );
    end component;

    signal a, b : std_logic_vector(3 downto 0);
    signal sum  : std_logic_vector(4 downto 0);
    signal c1, c2, c3 : std_logic;

    signal sum_int    : integer range 0 to 31;
    signal ones_digit : integer range 0 to 9;
    signal tens_digit : integer range 0 to 9;

    --------------------------------------------------------
    -- Функция перевода цифры 0..9 в код семисегментника
    -- Для DE2 обычно индикатор активный по нулю
    --------------------------------------------------------
    function to_7seg(d : integer) return std_logic_vector is
    begin
        case d is
            when 0 => return "1000000";
            when 1 => return "1111001";
            when 2 => return "0100100";
            when 3 => return "0110000";
            when 4 => return "0011001";
            when 5 => return "0010010";
            when 6 => return "0000010";
            when 7 => return "1111000";
            when 8 => return "0000000";
            when 9 => return "0010000";
            when others => return "1111111";
        end case;
    end function;

begin

    -- Разделяем вход SW на два числа
    a <= SW(3 downto 0);
    b <= SW(7 downto 4);

    --------------------------------------------------------
    -- 4-разрядный сумматор из 4 полных сумматоров
    --------------------------------------------------------
    fa0: full_adder port map(
        a    => a(0),
        b    => b(0),
        cin  => '0',
        s    => sum(0),
        cout => c1
    );

    fa1: full_adder port map(
        a    => a(1),
        b    => b(1),
        cin  => c1,
        s    => sum(1),
        cout => c2
    );

    fa2: full_adder port map(
        a    => a(2),
        b    => b(2),
        cin  => c2,
        s    => sum(2),
        cout => c3
    );

    fa3: full_adder port map(
        a    => a(3),
        b    => b(3),
        cin  => c3,
        s    => sum(3),
        cout => sum(4)
    );

    --------------------------------------------------------
    -- Перевод суммы в integer и разделение на десятки/единицы
    --------------------------------------------------------
    sum_int    <= to_integer(unsigned(sum));
    tens_digit <= sum_int / 10;
    ones_digit <= sum_int mod 10;

    --------------------------------------------------------
    -- Вывод на индикаторы
    --------------------------------------------------------
    HEX0 <= to_7seg(ones_digit);  -- единицы
    HEX1 <= to_7seg(tens_digit);  -- десятки

end beh;