Re: GS Emulator

[barryn@NETCOM.COM (Barry Nathan)]

Earlier in this thread, Michael Foegelle said:

>I believe the difference here is that the power PC MAC can't really be
>considered an "emulator" in the truest sense of the word, since I believe
>it consisted of an entire re-write/compilation of the MAC firmware on the
>Power PC so that it runs in native mode.  (I may be totally off on this but
>I thought that was part of the idea.)

They only rewrote the often-used parts of code. They're rewriting more and
more of it slowly, and a lot of extra emulated code is supposed to be
coming with System 8.

>Granted it still has to emulate the
>68030 or whatever processor to run the Mac software,

Close. 68020.

>but it's a much more
>integrated system than your typical emulator.  The hardware, etc, was designed
>to work Mac-like.

True.

>At any rate, I suspect a PC or PPC based 65816 emulator wouldn't be too hard
>to accomplish, and emulation rates would be about what our realtime rates are.
>GS video could be moderately emulated, but there wouldn't be most of the timing
>flags and interrupts available that allow tricks like 3200 color graphics to
>work right.  Using a Gravis Ultrasound, the GS sound shouldn't be too hard to
>emulate, but there aren't many PC users with GUS overall.  Still, those
>wanting to run GS software might go buy GUS's just for that purpose.  That
>still leaves emulating all the lousy soft switches and interrupts, not to
>mention having to copy Apple's ROMs to your emulator.

There could be an option to turn off some of the softswitch/interrupt
emulation so that the emulator could run faster. You could also try to
intercept jumps to ROM vectors and emulate parts of the ROM through PPC
instructions. A clean ROM that runs faster as well, but I don't know if the
FTA demos would still work...

>So unless Apple releases
>the copyright (unlikely)

Actually, Microsoft owns some of the ROMs (because of Applesoft BASIC, if I
remember correctly), but I could be wrong.

>or someone writes some clone ROMs that can withstand
>Apple's scrutiny (even MORE unlikely) that only leaves the people owning a GS
>already the opportunity to use the emulator.

Yes, but those GSes are probably going to die sooner than those PowerPCs.

>--
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Barry Nathan                                 Internet e-mail:barryn@netcom.com
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