Re: Is there a z80 emulator for the II's?

[nathan@cco.caltech.edu (Nathan Mates)]

In article <4lfhh7$7qs@bertrand.ccs.carleton.ca>,
Michael Quattrocchi <mquattro@chat.carleton.ca> wrote:
>Nathan Mates (nathan@cco.caltech.edu) wrote:
>>    Asm/disasm are one thing. An emulator is most definitely out from
>> this package though-- there's a _real_ z180 on the board. The original
>> guy keeps asking for a software emulator, which there has been no
>> evidence of whatsoever.

>has anyone ever seen one of these on the II's before (a software z80
>emulator, that is...) ? It'd be a shame to write such a neat application
>with the inherent need for a z80 hardware card when a sufficently compact
>code could do...

   Did you read what I said before? Software emulators are not some
magical thing that can run things at full speed-- they must deal with
translating all of the actions of the system. If you can get an Z80
emulator (non-recompiling or other fancy tricks) for the 6502 which
runs at 250Khz (i.e. 1/4 of 1Mhz), I'd be very surprised. Even with a
Zipped GS, it'd probably peak at 1Mhz on certain code.

   Further, the 6502 and Z80 were both designed around a 64K memory
space. You try and squeeze an emulator, some OS (needed to load the
emulator off disk unless you want to type it in each time), _and_ 64K
of Z80 address space into the 64K available of a ][+, and tell me what
you did. The solution to that is either more memory, or a Z80 card,
possibly with memory on the Z80 card. That's why Z80 cards were done,
not software emulators.

   By the time the GS came out, which was faster and had more than 64K
of easily accessible memory, Z80s were pretty much dead for general
use.  Embedded systems (such as the Z180 on a RamFAST or Second Sight,
or controlling the sound on a Sega Genesis) were the major uses of them.

   I've written some software emulators, and looked at other
emulators. Do you have such experience? Emulators are NOT simple or
tiny things to write-- take a look at the source code for 6502
emulators in C or asm. (One that I saw was a 500 line C file for just
the 6502 part, another few files for the //e emulation). If you
disbelieve me, write your own. You'll find that for a large part,
software emulation of hardware is a lot of grunge work to list all
possibly actions and behaviors. [One CS class I had here, I had to do
an emulator for a chip in Pascal-- and bitwise operations were not
supported in the Pascal compiler. That royally sucked.]

   This is the second time I've detailed out why the Apple II series
has no software Z80 emulators, but why real (i.e. hardware) chips were
popular. If you disagree with the technical reasons, please state what
and where you disagree with me, not simply repeating your request for
what you want. 

   There is nothing stopping you from writing your own, but what I'm
saying is that there has been no real need or demand for software
Z80 emulators.

Nathan Mates
-- 
<*> Nathan Mates http://www.ugcs.caltech.edu/~nathan/      <*>
# And he said to them, "To you has been given the secret of the
# Kingdom of God, but for those outside, everything comes in 
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