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library ieee;

use ieee.std_logic_1164.all;

use ieee.numeric_std.all;

entity timer is

  port(

       clk              : in std_logic;

                 areset                         : in std_logic;

                 we                                     : in std_logic;

                 din                                    : in std_logic_vector(7 downto 0);

                 adr                                    : in std_logic_vector(2 downto 0);

                 dout                                   : out std_logic_vector(7 downto 0));

end timer;

architecture behave of timer is

signal  sample  : std_logic;

signal  reset           : std_logic;

signal  cnt             : unsigned(63 downto 0);

signal  cnt_smp : std_logic_vector(63 downto 0);

begin

        reset <= '1' when (we = '1' and din(0) = '1') else '0';

        sample <= '1' when (we = '1' and din(1) = '1') else '0';

        process(clk, areset)    -- Carry generation

        begin

                if areset = '1' then

                        cnt <= (others => '0');

                        cnt_smp <= (others => '0');

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

                        cnt <= cnt + 1;

                        if sample = '1' then

--                              report "sampling" severity failure;

                                cnt_smp <= std_logic_vector(cnt);

                        end if;

                end if;

        end process;

        process(cnt_smp, adr)

        begin

                case adr is

                        when "000"      => dout <= cnt_smp(7 downto 0);

                        when "001"      => dout <= cnt_smp(15 downto 8);

                        when "010"      => dout <= cnt_smp(23 downto 16);

                        when "011"      => dout <= cnt_smp(31 downto 24);

                        when "100"      => dout <= cnt_smp(39 downto 32);

                        when "101"      => dout <= cnt_smp(47 downto 40);

                        when "110"      => dout <= cnt_smp(55 downto 48);

                        when others     => dout <= cnt_smp(63 downto 56);

                end case;

        end process;

end behave;