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

[mdj <mdj.mdj@gmail.com>]

On Aug 25, 3:10 pm, demp...@actrix.gen.nz (David Empson) wrote:
> 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:
>
> > > > On Aug 23, 10:37 am, Tempest <temp...@atariprotos.com> wrote:
>
> > > > > 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.
>
> > > > Do you have anything in slot 3? </longshot>
>
> > > I don't believe so, but I'll check tonight.
>
> > 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.
>
> Ah, that gives enough of a clue to work out what was probably going on.
>
> 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.
>
> 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).

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.

I (very quickly) perused the boot code on the Airheart image from
Asimov which is what gave me the idea.

Matt