-- C16 System On Chip Architecture
-- Copyright (C) 2003 by Cole Design and Development all rights reserved

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

entity rtc is
    Port (
	 	enable : in std_logic;									-- rtc enable
  		clock_sec : in std_logic;								-- 1 Hz timer tick
		reset : in std_logic;									-- reset input
		cs : in std_logic;										-- chip select
		read : in std_logic;										-- read data
		write : in std_logic;									-- write data
		data_in : in std_logic_vector (15 downto 0);		-- bytes read
		data_out : out std_logic_vector (15 downto 0));	-- bytes written
end rtc;

architecture Behavioral of rtc is
   signal count_sec: unsigned(5 downto 0);				-- seconds
   signal count_min: unsigned(5 downto 0);				-- minutes
   signal count_hr: unsigned(4 downto 0);					-- hours
   signal count_day: unsigned(4 downto 0);				-- days (TODO: always assumes 30 days)
   signal count_month: unsigned(3 downto 0);				-- months
   signal count_year: unsigned(15 downto 0);				-- years

begin

	process(enable, cs, read, count_sec)
	begin
		if read = '1' and cs = '1' and enable = '1' then
			data_out <= "0000000000" & std_logic_vector(count_sec);
		else
			data_out <= "ZZZZZZZZZZZZZZZZ";
		end if;
	end process;

	process(clock_sec, reset, enable)
	begin
		if reset = '1' or enable = '0' then
			count_sec <= "000000";
			count_min <= "000000";
			count_hr <= "00000";
			count_day <= "00000";
			count_month <= "0000";
			count_year <= "0000000000000000";
		elsif rising_edge(clock_sec) then
			if count_sec < 59 then
            count_sec <= count_sec + "000001";
			else
            count_sec <= "000000";
				if (count_min < 59) then
					count_min <= count_min + "000001";
				else
					count_min <= "000000";
					if (count_hr < 23) then
						count_hr <= count_hr + "00001";
					else
						count_hr <= "00000";
						-- TODO: real month lengths, not just 30
						if (count_day < 29) then
							count_day <= count_day + "00001";
						else
							count_day <= "00000";
							if (count_month < 11) then
								count_month <= count_month + "0001";
							else
								count_month <= "0000";
								count_year <= count_year + "0000000000000001";
							end if;
						end if;
					end if;
				end if;
			end if;
		end if;
	end process;

end Behavioral;