Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!rutgers!cbmvax!daveh
From: daveh@cbmvax.commodore.com (Dave Haynie)
Newsgroups: comp.sys.amiga.hardware
Subject: Re: RISC Amiga
Keywords: well there's going to be a RISC Mac!!
Message-ID: <15500@cbmvax.commodore.com>
Date: 31 Oct 90 18:47:01 GMT
References: <1156@iceman.jcu.oz> <22914@grebyn.com> <16105@hydra.gatech.EDU>
Reply-To: daveh@cbmvax.commodore.com (Dave Haynie)
Organization: Commodore, West Chester, PA
Lines: 42

In article <16105@hydra.gatech.EDU> ken@dali.gatech.edu (Ken Seefried iii) writes:

>RISC processors very much lend themselves to emulating other machines
>(within limits).  A RISC simulator of an Amiga, while probably not
>easy, is certainly doable by reasonably sharp team.  Hell, it might be
>easier than SoftPC since the 68k instruction set is so much cleaner
>and more orthoginal that the Intel rubbish.

The problem with these simulators has never been the simulation of the CPU
itself.  I've run three software simulators on my Amiga: PC, C64, and CP/M.
The first two, commercial products, ran pretty slowly.  The CP/M emulator
was plenty fast.  Why?  Because the Z-80 is about all it has to emulate, the
rest of the system is handled via system calls that can be translated into
Amiga system calls.  The PC emulator has to emulate not only the 80x86
instruction set, but all the I/O chips at the register level.  So that 
wordprocessor that works just dandy on a real PC now dies in emulation as it
sits there polling the keyboard controller chip, directly, 60 times a
second.  Similarly, that raster interrupt plus busy wait loop that used
to work on the VIC-II chip in a real C64 now just plain fails with the
software simulation of the VIC-II's registers sitting down underneath it.

As for Amiga simulation, if you build a real AmigaRISC machine, you might be
able to avoid many of these emulation problems.  Emulating the 680x0 would
not be a big deal.  If it's an AmigaRISC of some kind, it should have a chip
set that's similar enough to the Amiga's chip set to not need register level
emulation of all those registers.  Similarly, the Amiga OS is very function
call oriented; for the most part, only games are directly banging on the
hardware.  So for library functions, you get direct translations into RISC
versions of those, rather than having to emulate all of those 68000 opcodes.
You would most likely have trouble with anything that demanded too much real
time performance, but a good portion of stuff could probably be made to run.
That emulation box, though, would still be a considerable amount of work.
But in general, as an OS depends on only CPU and function calls, it can be
reasonably emulated.  As you add hardware register or time dependency, it
gets increasingly hairier.

>	ken seefried iii	"A snear, a snarl, a whip that

-- 
Dave Haynie Commodore-Amiga (Amiga 3000) "The Crew That Never Rests"
   {uunet|pyramid|rutgers}!cbmvax!daveh      PLINK: hazy     BIX: hazy
	Standing on the shoulders of giants leaves me cold	-REM