Re: [steem] Processors
- From: "Summa" <flotorian@xxxxxxxxxx>
- To: steem@xxxxxxxxxxxxx
- Date: Wed, 21 Aug 2002 18:06:38 +0200
On 19 Aug 2002 at 17:43, Steem Authors wrote:
> Hi Summa,
>
> > > Would it make a lot of difference for a programmer? After all the main
> > > benefit of an 030 was the speed increase, and there is already an option
> in
> > > Steem to do that.
> >
> > The 030 has an improved processor instruction set that will speed up
> > such programms on real 030 machines and probably even increase the
> > speed of the emulation since those commands should be easier to
> > emulate and therefore needs less processing power...
>
> Unfortunately the increased code size could slow the whole of Steem down
> quite a bit, plus all the checks we would need for what type of processor is
> being used (24-bit or 32-bit addresses, that would have to be checked
> everywhere).
The 68k already works with 32-Bit addresses and just ignores the most
significant byte of the address registers. Your emulation shouldn't
work any different otherwise you would have serious compatiblity
problems, so no checks should be needed since I/O adresses and
everything else stays the same...
I'm not sure if I understand how the code size would affect the speed
since my guess is that Steem already don't fit completely into the
processor cache...
> > My guess is that the emulator programmers of the Amiga Emulator UAE
> > had some reasons to emulate the multiple processor types as well...
>
> Well the later Amigas were more popular than the later STs, so there is more
> software available and more people with a reason to want them. I'm not sure
> but I would think it would be easier to implement different processors in an
> emulator that isn't trying to be 100% cycle accurate too.
I think the Amiga Emulator is cycle accurate as well, since I don't
think the demo programmers on this computer did a more protable code
than the ones on the ST. For the 030 emulation mode it don't have to
be cycle accurate. I'm not sure since I'm far to long haven't done
any ST programming but I think it might be enough for most of the
cases to check for the 030 instructions when normaly an illegal
instruction would occour since only some minor changes were made to
the 68k set. The most tricky part is probably to implement the Memory
Management Unit at least if you're not already using a table for
memory management...
...Summa
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