Re: ROM 3 //gs issues

[Tom Greene <tom@cowgod.org>]

On Sep 12, 9:52 pm, "Michael J. Mahon" <mjma...@aol.com> wrote:
> Nels Bruckner wrote:
> > On Sep 6, 2:33 pm, Linards Ticmanis <ticma...@gmx.de> wrote:
> >> Nels Bruckner wrote:
> >>> The next thing I could try is swapping in a second set of ROM 3 ROM
> >>> chips, which I don't have.  My usualy saviors in this kind of
> >>> situation, Reactive Micro, don't seem to carry ROM 3 replacements.
> >>> Any suggestions?
> >> On an 8-bit Apple I'd just write and run a quick Applesoft program to
> >> checksum the ROM (sum or EOR of all bytes), test it on an emulator and
> >> on the real system and see if the results differ.
>
> >> I don't know the IIgs well enough to know whether the entire ROM is
> >> readable from Applesoft. You might need assembly, but I assume it would
> >> be short enough to just enter from the CALL -151 monitor.
>
> >> --
> >> Linards Ticmanis
>
> >      Could certainly do that, but whether pass or fail it wouldn't
> > give me much new info.
>
> Actually, it will verify whether your machine is reading its ROM
> correctly, which is an issue.
>
> >      I did discover that the application failures I was seeing were
> > because (duh) I hadn't installed a RAM card in this machine.  Now that
> > the machine has 2MB of RAM it runs Dungeon Master, etc, just fine.
> > Which really just leaves me with the curious fact that the diagnostic
> > software reports a failure of the CPU/ROM validation step, since the
> > machine seems to function just fine.
>
> It's not hard to imagine a fault which the software you have tried
> does not "exercise", or which it tolerates.
>
> CPU/ROM validation must be very early in the self-test sequence, so
> most of the test may not even be running.
>
> >  I'm keeping my eyes open for a
> > second, dirt cheap ROM 3 machine (I think I got this one for $20+p/h)
> > to swap ROMS with but, in the meantime, anyone know where I can pick
> > up a set of ROM 3 chips?
>
> Running the checksum that Linards suggested, and comparing it with
> the same test run on an emulator configured for ROM 3 will answer
> the question of whether or not the ROM is bad.
>
> Swapping the processor is just as easy as swapping the ROM, and
> you can use any version of a IIgs for the swap.
>
> -michael
>
> AppleCrate II: An Apple II "blade server"!
> Home page:  http://members.aol.com/MJMahon/
>
> "The wastebasket is our most important design
> tool--and it's seriously underused."

Interestingly, KEGS appears to modify the ROM 3 code, resulting in
checksums which differ from the actual hardware.  I don't know if any
other emulators do the same.

Tom