Re: dot sys

[dempson@actrix.gen.nz (David Empson)]

Jim Pendarvis <jpendarv@patriot.net> wrote:

> System programs must load at $2000. You will need to load your code there
> and relocate it as necessary. The program name does not need to contain
> .sys or system, but the filetype must be $FF.

It is also worth noting that your program cannot rely on anything which
might have been left behind by another application; in particular, no
parts of BASIC.SYSTEM can be used from a SYS file.  You must use the
ProDOS MLI (Machine Language Interface) for all file I/O.

There are several requirements for dealing with the MLI which you need
to take into account, such as initializing the memory bitmap in the
global page.  (If you don't do this, you could run into problems with
any file I/O calls.)  You should also make sure the reset vector
($3F2-$3F4) is pointing somewhere sensible within your application.

When your SYS file is ready to quit, it must issue a QUIT call to the
MLI.  This will transfer control to whichever program selector is
currently installed.