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

[Dirk Thierbach <dthierbach@usenet.arcornews.de>]

Michael J. Mahon <mjmahon@aol.com> wrote:
> Dirk Thierbach wrote:
>> sicklittlemonkey <Nick.Westgate@gmail.com> wrote:
>>>On Mar 19, 7:03 pm, Dirk Thierbach <dthierb...@usenet.arcornews.de>
>>>wrote:

>>>>So how did they do that?

>>>By slowing down to 1MHz when certain I/O locations were accessed.

>> That's what I thought. So, in other words, hardware accelerators can't
>> do it correctly, either, unless they run at 1MHz.

> No, by automatically controlling their speed (which emulators apparently
> aren't smart enough to do) they work correctly.

If you can specify exactly *how* they should do that, than emulators
can do that, too. Having a list of address that slow them down automatically 
to 1MHz is easy to implement. But then, it's not necessary -- the user
can just manually switch to 1 MHz.

> In the specific case I'm trying to use, an accelerated machine correctly
> samples floating video data and can pace itself to the video framerate.

Which would be still possible in the scheme outlined. It's just the
fact that the "emulated" video framerate isn't constant (to ensure the
correct behaviour for most programs, it would vary with acceleration
speed), and is not related to the real world.

> Among other things, this allows a simple subroutine to "wait for
> X frames" before returning, allowing constant time delays for users
> to do something human, 

If you're writing a new program anyway, and if all you want is constant
time delay and not something fancy like split-screen, then it would be
much better to just use an "emulated" clock with sufficient precision
in a "pseudo"-card as provided for example by one of the Linux apple
emulators.

- Dirk