Re: Integer BASIC & the IIgs?

[nparker@cie-2.uoregon.edu (Neil Parker)]

In article <5orshb$rvf@news.asu.edu> adam.myrow@asu.edu writes:
>I remember somebody saying once that emulating an Apple II on an Apple 
>IIgs would be pointless.  However, I think that's how Integer BASIC 
>works.  If you do a "CALL -151" from the ">" prompt, you end up in what 
>is apparently the original Apple II monitor.  Also, if you set the system 
>speed to normal and do a control-G or any other function that makes the 
>GS beep, it's the old pre-GS beep.  This is with the old 1980 DOS 3.3 
>master.  This was just another piece of useless trivia.

Yes, you do get that behavior if you run Integer BASIC on a IIGS...at least
you do if you boot Integer from the original (1980) DOS 3.3 System Master
(if you use the later (1983) System Master, the monitor behaves just like
the IIGS monitor).

But this isn't because the GS is "emulating" an older machine...it's because
the disk image of Integer BASIC that comes on the old DOS 3.3 System Master
includes the image of the old II+ Autostart ROM.  So naturally, CALL-151
from Integer enters the Autostart ROM monitor code, not the native IIGS
monitor code.  Likewise with control-G.

Try this:  Boot the old DOS 3.3 System Master, go into Integer, and type
PR#3.  Then press ESC control-Q.  Notice that control-G now produces the
native IIGS beep, and CALL-151 now enters the native IIGS monitor.  The
old Apple II+ behavior disappeared because the PR#3 copied the native IIGS
monitor ROM code onto the language card.


There's nothing really interesting going on there...it's just the 65816
executing the old ROM code instead of the new ROM code.  The "emulate a II
on a IIGS" thread a while back was talking about something entirely
different--that person wanted to write a complete 6502 emulator in 65816
machine language, so there would be a "virtual 6502" interpreting (rather
than executing directly on the 65816) 6502 code, and emulating the behavior
of the old Apple II softswitches and video buffers.

I still maintain, as I did then, that such an emulator is an exercise in
pointlessness...completely emulating *any* computer system requires a
much heftier host CPU than we have in the IIGS, unless you don't mind an
emulator that runs like it's drowning in molasses.

               - Neil Parker
-- 
Neil Parker, nparker@{cie-2,cie}.uoregon.edu, http://cie-2.uoregon.edu/~nparker
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