entity address_decoder is
  port ( addr : in work.cpu_types.address;
         status : in work.cpu_types.status_value;
         mem_sel, int_sel, io_sel : out bit );
end entity address_decoder;

--------------------------------------------------

architecture functional of address_decoder is

  constant mem_low : work.cpu_types.address := X"000000";
  constant mem_high : work.cpu_types.address := X"EFFFFF";
  constant io_low : work.cpu_types.address := X"F00000";
  constant io_high : work.cpu_types.address := X"FFFFFF";

begin

  mem_decoder :
    mem_sel <= '1' when ( work.cpu_types."="(status, work.cpu_types.fetch)
                          or work.cpu_types."="(status, work.cpu_types.mem_read)
                          or work.cpu_types."="(status, work.cpu_types.mem_write) )
                        and addr >= mem_low
                        and addr <= mem_high else
               '0';

  int_decoder :
    int_sel <= '1' when work.cpu_types."="(status, work.cpu_types.int_ack) else
               '0';

  io_decoder :
    io_sel <= '1' when ( work.cpu_types."="(status, work.cpu_types.io_read)
                         or work.cpu_types."="(status, work.cpu_types.io_write) )
                       and addr >= io_low
                       and addr <= io_high else
              '0';

end architecture functional;