-------------------------------------------------------------------------------
-- MaxDaySelector.vhd
-- Sydney Tang
-- 1998 October 17
-- 
-- Entity to select the maximum number of days according to the year and month.
--
-- This entity takes as its inputs the value of the month (1 to 12) and the
-- first two bits of the value of the year. It outputs the number of days that
-- there are in the given month.
--
-- Leap years are detected by reading the two least significant bits in the
-- year. Any number that is divisible by 4 would have "00" for these two bits.
-------------------------------------------------------------------------------

library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_arith.all;
use ieee.std_logic_unsigned.all;

library work;
use work.BCD_Package.all;
use work.Time_Package.all;

entity MaxDaySelector is
    port(
      Month: in std_logic_vector(1+BCD_WIDTH-1 downto 0);
      Century2LSB: in std_logic_vector(1 downto 0);
      Year2LSB: in std_logic_vector(1 downto 0);
      DecadeYear: in std_logic_vector(2*BCD_WIDTH-1 downto 0);
      MaxDay: out std_logic_vector(2*BCD_WIDTH-1 downto 0)
    );
end MaxDaySelector;

architecture selector of MaxDaySelector is

begin

  SelectMaxDay: process(Month) is
  begin

    case Month is
      when JAN =>
        MaxDay <= THIRTY_ONE_DAYS;
      when FEB =>
        case Year2LSB is
          when "00" =>   -- year is divisible by 4 -> possible leap year
            if DecadeYear = "00000000" then
              case Century2LSB is
                when "00" => -- century 
                  MaxDay <= TWENTY_NINE_DAYS;
                when others =>
                  MaxDay <= TWENTY_EIGHT_DAYS;
              end case;
            else
              MaxDay <= TWENTY_NINE_DAYS;
            end if;
          when others => -- not divisible by 4 -> normal year
            MaxDay <= TWENTY_EIGHT_DAYS;
        end case;
      when MAR =>
        MaxDay <= THIRTY_ONE_DAYS;
      when APR =>
        MaxDay <= THIRTY_DAYS;
      when MAY =>
        MaxDay <= THIRTY_ONE_DAYS;
      when JUN =>
        MaxDay <= THIRTY_DAYS;
      when JUL =>
        MaxDay <= THIRTY_ONE_DAYS;
      when AUG =>
        MaxDay <= THIRTY_ONE_DAYS;
      when SEP =>
        MaxDay <= THIRTY_DAYS;
      when OCT =>
        MaxDay <= THIRTY_ONE_DAYS;
      when NOV =>
        MaxDay <= THIRTY_DAYS;
      when DEC =>
        MaxDay <= THIRTY_ONE_DAYS;
      when others =>
        MaxDay <= ONE_DAY;
    end case;
  end process SelectMaxDay;
end selector;