Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!sdd.hp.com!apollo!mort
From: mort@apollo.HP.COM (Stephen Moriarty)
Newsgroups: comp.sys.apple2
Subject: Re: Quadram APIC-A //e compatibility & code debugging
Message-ID: <510db948.20b6d@apollo.HP.COM>
Date: 18 Apr 91 21:33 GMT
References: <50a3ec40.20b6d@apollo.HP.COM> <1991Mar30.131325.24160@lynx.CS.ORST.EDU> <1991Apr02.223712.13868@convex.com>
Sender: root@apollo.HP.COM
Reply-To: mort@apollo.HP.COM (Stephen Moriarty)
Organization: Hewlett-Packard Apollo Division - Chelmsford, MA
Lines: 19

In article <1991Mar30.131325.24160@lynx.CS.ORST.EDU>:
>It seems that a common technique used by interface cards to find out what
>slot they're in is to call an RTS instruction in the monitor and examine
>the return address that the JSR pushed onto the stack.  Apple guarantees
>that there will always be an RTS at $FF58 for this very purpose.
>Unfortunately, the Tymac doesn't call $FF58--it calls $FDFF instead.  On
>the Apple ][+ there was an RTS at $FDFF, so everything worked just fine.
>However, on the enhanced //e, that RTS was replaced with some other
>instruction (I think it was a NOP), so instead of returning execution fell
>through to $FE00, which is part of the monitor's memory dump routine.

        BINGO! I just changed two references to $FDFF in the
driver firmware to $FF58, reprogrammed the EPROM, and voila! it
works! Thanks for the help.


ARPA: mort@apollo.hp.com        UUCP: ...{decvax, umix, mit-eddie}!apollo!mort
Apollo, a subsidiary of Hewlett Packard, 300 Apollo Drive, Chelmsford, MA. 01824
              Argue for your limitations, and they are yours.