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Newsgroups: comp.sys.apple2
Subject: Re: Initializing 8-bit SYS programs
Message-ID: <1993Mar3.064553.14757@actrix.gen.nz>
From: David.Empson@bbs.actrix.gen.nz
Date: Wed, 3 Mar 1993 06:45:53 GMT
Sender: David.Empson@actrix.gen.nz (David Empson)
References: <1993Mar1.233904.5916@msuvx2.memst.edu>
Organization: Actrix Information Exchange
Lines: 48

In article <1993Mar1.233904.5916@msuvx2.memst.edu> connolly@msuvx2.memst.edu writes:
> I've noticed that certain 8-bit system programs won't run right if
> launched after certain other system programs.  ...

Agreed.  One that particularly annoys me (but I haven't been able to
isolate fully) is ShrinkIt, which crashes into the monitor SOMETIMES
on startup.

When writing your own SYS programs, I'd say be as pessimistic as
possible - assuming NOTHING about the machine's state and initialize
everything.  If you're using text mode, call $FB2F, $FE89 and $FE93
before trying to use COUT, etc.  If you're on a IIe, 80-column mode
might be active, so manually disable 80-column store and 80-column
video, and select the primary character set.  (The IIgs and possibly
IIc will clean up after 80-column mode if you call $FE93.)

You should also make sure the stack pointer is set to $01FF (LDX #$FF,
TXS).  I discovered that Aztec C doesn't do this, and paritcularly on
the IIc, enhanced IIe and IIgs, you tended to get random crashes when
the stack eventually worked its way down to $0100 and an interrupt
occurred.

You can be reasonably sure that the ProDOS entry conditions will be OK
- the pathname of the application will be at $0280, but it might be a
partial pathname.

You should initialize the ProDOS memory bitmap as required.

There probably are guidelines for programs entering/exiting in the
ProDOS Technical Reference Manual and/or ProDOS technical notes
(handling of the /RAM disk comes to mind).  I haven't read them recently.

Can't think of anything else off-hand.

> So at least I would like to know: what should *my* text-based system
> programs initialize so that they'll run right?  Is any different
> initialization needed for a program with graphics-only display?
> (I program inAztec C and assembler on a IIe and run on that machine and
> on a IIgs.)

I don't know how you'd do this in Aztec C - I haven't used any of its
standard I/O routines in much code (I wrote my own).

-- 
David Empson

Internet: David.Empson@bbs.actrix.gen.nz    EMPSON_D@kosmos.wcc.govt.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand