package data_user
is

   --  as before

   data_ptr : data_t_ptr;

end data_user;

.......
package body data_user
is

   .....

   -- set address for the data record
   procedure set_address
     (   addr : system.address )
   is
   begin
      data_ptr := to_ptr( addr );
   end;

   procedure handle_new_data
   is
   begin
      -- work with data_ptr.all
   end;

end data_user;