Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cs.utexas.edu!samsung!brutus.cs.uiuc.edu!apple!dlyons
From: dlyons@Apple.COM (David A. Lyons)
Newsgroups: comp.sys.apple
Subject: Re: Prodos 8 Quit code
Message-ID: <38428@apple.Apple.COM>
Date: 7 Feb 90 21:11:36 GMT
References: <7660@wpi.wpi.edu> <38347@apple.Apple.COM> <7733@wpi.wpi.edu>
Organization: Apple Computer Inc, Cupertino, CA
Lines: 38

In article <7733@wpi.wpi.edu> greyelf@wpi.wpi.edu (Michael J Pender) writes:
>I'm not using a GS.  You mean to tell me that to use the enhanced 
>prodos 8 quit call, I have to have prodos 16 in memory?

Yes.  (I can't guarantee that ProDOS 8 booted directly will -never- support
the enhanced QUIT call, but it certainly doesn't now, as of v1.8.)

>How do sytem programs chain to each other then?

See chapter 5 of the _ProDOS 8 Technical Reference Manual_.  Summary:
store the pathname of the next program at $280.  Close all open files.
Clear the system bitmap so that pages 0, 1, 4-7, and $BF are protected,
but all other pages are available.  Read in the next program to $2000,
and JMP to $2000.

Note that "read in the program at $2000" is a little tricky, since you
don't want to overwrite your code in the process.  This means you need
to copy a section of code down below $2000 for reading in the file and
jumping to it.  (If you put it way up close to $BF00 instead, there will
be a limit to the size of a SYS file you can chain to!  This is actually
important, since there are programs that are that long.)

Defensive programmers clean things up even more:  I put the screen
in 40 columns, do PR#0 and IN#0, full text window, NORMAL mode,
stack pointer = $FF.

>Michael J Pender Jr  Box 1942 c/o W.P.I. W.O.S. is not dead.
>greyelf@wpi.bitnet   100 Institute Rd.   ...its time to get started,
>greyelf@wpi.wpi.edu  Worcester, Ma 01609 there is much to be done.
-- 

 --David A. Lyons, Apple Computer, Inc.      |   DAL Systems
   Apple II Developer Technical Support      |   P.O. Box 875
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