Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!csd4.milw.wisc.edu!bionet!ames!oliveb!apple!dlyons
From: dlyons@Apple.COM (David Lyons)
Newsgroups: comp.sys.apple
Subject: Re: ProDOS block 0
Message-ID: <33761@apple.Apple.COM>
Date: 5 Aug 89 23:49:10 GMT
References: <113300095@uxa.cso.uiuc.edu>
Organization: Apple Computer Inc, Cupertino, CA
Lines: 31

In article <113300095@uxa.cso.uiuc.edu> krb20699@uxa.cso.uiuc.edu writes:
>I have a lot of software on 5.25" disks from my IIe that I use a lot on
>my IIgs (fast!)  When I got my machine, I set the bootup slot to 6, and booted
>up my old software nicely.  When there wasn't a disk in the drive, it would
>boot up slot 5 (my 3.5" drive) automagically, after rattling the 5.25" drive.
>     Later, I heard from someone on a local BBS that their machine did NOT poll
>to slot 5 after finding an invalid/nonexistent disk in slot 6.  Could this be
>a difference between the gs ROMsets (00/01) or something else?

Does the other person's machine have a Disk II card in slot 6?  The ROM on those
never gives up...it just has faith that you'll eventually insert a bootable
disk.  The port 6 firmware in the GS (regardless of ROM version) gives up and
passes control to the next slot.

>For this person, I decided to write some code to block 0 of a ProDOS disk
>that would boot up slot 5 without having to change the Control Panel setting
>from a slot 6 bootup to slot 5. I tried the following assembly at byte 0 of
>block 0: [...]

You need to put a $01 at byte 0 and put your code starting at byte 1.  I
suggest simply JMP $FABA ("SLOOP," Disk controller slot search loop, as
guaranteed on page 234 of the Apple IIgs Firmware Reference).

 --Dave Lyons, Apple Computer, Inc.          |   DAL Systems
   AppleLink--Apple Edition: DAVE.LYONS      |   P.O. Box 875
   AppleLink--Personal Edition: Dave Lyons   |   Cupertino, CA 95015-0875
   GEnie: D.LYONS2 or DAVE.LYONS         CompuServe: 72177,3233
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   My opinions are my own, not Apple's.