Re: Apple emulators that support "floating bus" video sensing?

["Michael J. Mahon" <mjmahon@aol.com>]

sicklittlemonkey wrote:
> On Mar 19, 4:22 am, "Michael J. Mahon" <mjma...@aol.com> wrote:
>
> > So, this is actually an emulation bug.
>
>
> This is perhaps the first time that I can say in all seriousness that
> this is a feature, not a bug! We are not emulating a ZIP chip or
> accelerator card, though I can see this would be attractive in certain
> situations.
>
>
> > If we assume that the emulator is supposed to emulate an Apple II
> > with an accelerated *processor*, then the emulated cycle count should
> > be divided by the acceleration ratio before being used to compute the
> > current "phantom" video byte.
>
>
> "Maximum speed" emulation would be problematic. The alternative of
> decoupling (host) video generation from emulated video generation
> exposes some difficult synchronization issues for floating bus
> emulation. Emulator authors have taken the easiest route that provides
> value.
>
>
> > As it is, it emulates an Apple II with both the processor and the
> > video refresh accelerated--and there is no such beast!
>
>
> Acceleration of the entire machine gives the benefit of peripheral
> card acceleration, the most useful result being fast disk access. A
> coprocessor (eg Z80) would similarly benefit. Sound is adversely
> affected, of course, but this is usually not important.

Well, the consequence is that any program using animation needs
to run at 1MHz emulated speed.  This is not the case for an
accelerated machine.

Oh, well--I hoped I had found a way to combine fast game computation
with correct-speed animation and delays.  Apparently not for emulators.

Most accelerators went to some lengths to achieve implementation of
processor acceleration combined with standard speed sound and (if
needed) disk access.  This allows even time-critical cycle-counting
code to be usefully run on an accelerated machine with some care.

Too bad that's such a challenge for emulators.  ;-(

-michael

NadaPong: Network game demo for Apple II computers!
Home page:  http://members.aol.com/MJMahon/

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