| From: | Alastair M. Robinson |
| Date: | 2 Sep 2000 at 12:54:31 |
| Subject: | Re: Amiga PPC UAE |
Hi Don,
>> Yep - but emulating Paula's sample-replay isn't hard. The modulation
>> stuff for AM/FM synthesis would be a lot more difficult - but does
>> anyone know of software which actually used this capability? (Maybe
>> PlaySID?)
> You're missing the point. It's not that imitating the sound from Paula
> is hard. (Although it's not as easy as you might think.)
Well I guess the Amiga's flexibility with regard to replay period might
cause problems with sample data having to be resampled...
My point was that throwing the address, length and replay-rate of a chunk of
sample data at an audio subsystem would be a *lot* faster, albeit much less
compatible, than fetching the audio data two bytes at a time in a simulation
of the A500's DMA cycles!
> The problem is that if the software is using Amiga hardware, every
> single memory access in the emulation has to be checked to see if it is
> actually a hardware read/write, so it can be escaped to an emulation
> routine.
Hmmm. Good point - I hadn't considered this. I suppose under a flexible
enough operating system this could be done with MMU traps? In fact, I seem
to remember a few years back someone talking on a newsgroup about the
possibility of using an MMU to emulate AGA on gfx-card systems. Nothing
ever came of it though.
> It's the checking that slows things down. The clever part of the
> Transmeta technology is that they found a way to minimise these delays,
> as explained in the Transmeta patents. This is not done in Amiga
> emulators.
Hmmm. I must read those patents sometime.
> Whether it could be, I don't know.
Without infringing the patents? ;^p
> Of course if the 68000 had separate addresses for hardware ports, like
> the Z80, there would be no problem. Puttting hardware in the same address
> range as RAM was a short-sighted decision. The Z80 has a specific set of
> commands for hardware access, so they can be easily converted in an
> emulation.
I somehow doubt that ease of emulation was the primary motivation in the
design ;-) Seriously though, x86 has seperate IO space and memory space
too, doesn't it?
> Why has nobody ever written an Atari ST emulation for the Amiga? Same
> problem, I think.
There are at least two - but the one I've got only works on A500 and needs
two disk-drives. I think the other one is on Aminet, but needs the ROM to
be grabbed from a real ST.
All the best,
Why can't we just spell it orderves?
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