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

["mressl@gmail.com" <mressl@gmail.com>]

Hello Michael,

I am emulating VBL and video scanner accesses through the floating bus
in AppleIIGo (the Apple II emulator I'm working on), and it *is*
correlated to screen refresh. There's also support for PAL and NTSC.

Unfortunately I am still working on the architecture of the emulator,
as it turned out that emulating the IIgs was far more ambitious than
what I had predicted. But the foundation is almost done, so once it
works again on a IIe, I'll update the featured download on
http://code.google.com/p/appleiigo/, and let you know!

Marc.-

On Mar 18, 4:20 am, "Michael J. Mahon" <mjma...@aol.com> wrote:
> I asked this question about a week ago in the emulators group, but the
> only thing I learned since then is that the latest version of AppleWin
> supports the sensing of video refresh bytes, but the time of sensing is
> unrelated to the actual emulator video refresh.
>
> The reason I'm asking is that I have written some code that does
> animation, and needs an absolute time reference (as opposed to cycle
> counts on accelerated machines or emulators).
>
> The objective is not to do something sophisticated, like avoid tearing
> of the animation (though that would be nice), but simply to cause it to
> run at its intended speed, regardless of the speed of the processor
> (emulated or real).
>
> Polling VBL works on an Apple //e, but *only* on a //e, since later
> machines de-implemented VBL polling in favor of VBL interrupts.
>
> Video byte sensing (the "vaporlock" or "Apple Split" approach) works
> on all real Apple II's, and achieves the desired absolute 1/60th
> second time reference.
>
> Since so many people use emulators these days, I was hoping that the
> same technique would work on at least one popular PC and one popular
> Mac emulator.
>
> I think AppleWin may work on the PC, but if it accelerates the "virtual
> video" as it accelerates the processor, then it may not.
>
> All the reasonable uses I can think of for video sensing and VBL sensing
> are related to an absolute time base, and should not be subject to
> acceleration (just as it is not in a real Apple II), but I'm not sure
> that emulator writers agree...
>
> What I'd like to know is which emulators *do* keep the emulated video
> period at 1/60th second (or 1/50th for PAL ;-).
>
> -michael
>
> NadaPong: Network game demo for Apple II computers!
> Home page:  http://members.aol.com/MJMahon/
>
> "The wastebasket is our most important design
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