Re: Airheart and Prince of Persia Not Detecting Memory on My IIe

[Tempest <tempest@atariprotos.com>]

On Aug 25, 7:18 am, mdj <mdj....@gmail.com> wrote:
> On Aug 25, 3:10 pm, demp...@actrix.gen.nz (David Empson) wrote:
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> > Tempest <temp...@atariprotos.com> wrote:
> > > On Aug 24, 9:26 am, Tempest <temp...@atariprotos.com> wrote:
> > > > On Aug 24, 4:27 am, mdj <mdj....@gmail.com> wrote:
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> > > > > On Aug 23, 10:37 am, Tempest <temp...@atariprotos.com> wrote:
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> > > > > > Anyone have any idea as to what the problem could be?  I've reseated
> > > > > > every chip and card, so I'm starting to wonder if something is blown
> > > > > > that I can't see.  But the system passes all diagnostic tests.  This
> > > > > > is really weird.
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> > > > > Do you have anything in slot 3? </longshot>
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> > > > I don't believe so, but I'll check tonight.
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> > > Eureka!  I had my mouse card in slot 3 instead of slot 5 where it
> > > normally is.  I must have put it back wrong when I was swapping things
> > > out last year.  I have no idea why this would cause the Apple to not
> > > see the 128K of memory, but apparently it does.  Go figure.
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> > Ah, that gives enough of a clue to work out what was probably going on.
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> > A mouse card in slot 3 would block access to the 80-column firmware,
> > including the AUXMOVE and XFER entry points for accessing the main 48K
> > region of auxiliary memory. This would prevent some programs from being
> > able to use auxiliary memory.
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> > ProDOS might still be able to use auxiliary memory as a RAM disk,
> > because the /RAM driver lives in the language card area so it can
> > control the main 48K soft switches directly. It has to implement its own
> > code for using auxiliary zero page and stack anyway, and that part runs
> > from auxiliary memory (somewhere in $0200-$03FF if  I remember right).
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> ProDOS applies its own logic to slot 3, and if it doesn't find a card
> that implements the Pascal 1.1 protocol and declares itself interrupt
> aware, it switches the built in firmware instead, which it would for a
> mouse card. "Standard" ProDOS software would then behave normally.
> This seems to be pretty good behaviour, in that the machine will
> behave as expected for older DOS software intended for the original
> Apple ][, but switch to a configuration more likely to work for newer
> software.
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> I (very quickly) perused the boot code on the Airheart image from
> Asimov which is what gave me the idea.
>
> Matt

Very cool.  So now I guess we know not to put mouse cards in slot 3.
After I originally posted about my success I thought about for a bit
and came to a similar conclusion that it must have something to do
with the 80 column firmware because that's the only thing that makes
slot 3 special.  The rest I couldn't figure out though.

Tempest