phoenix@ms.uky.edu (R'ykandar Korra'ti) (11/23/89)
Article 22689 of comp.sys.atari.st:
Path: ukma!rex!samsung!uunet!mcsun!unido!uklirb!incas!hoenig
From: hoenig@incas.UUCP (Helmut Hoenig)
Newsgroups: comp.sys.atari.st
Subject: 6502 - the ultimate (?) emulation
Message-ID: <3189@incas.UUCP>
Date: 21 Nov 89 10:10:51 GMT
Distribution: comp
Organization: University of Kaiserslautern, W-Germany
Lines: 52
Posted: Tue Nov 21 11:10:51 1989
Is there any use of a VIC20-Emulation on the ATARI ST ?
I wrote one to test a new kind of emulation: The 6502-code of the VIC20-
Machine is not interpreted the usual way. It gets *translated* in 68000-Code
at run-time. That means: If a statement is reached for the second time, it is
already translated. This gets very difficult, especially if self-modifying
code is alowed (already the Commodore-Basic uses it).
My final results:
- It needs a *lot* of memory:
The memory of the Atari is sliced in 8-byte slots of code for every
VIC20-Byte (unfortunatly, that's not enough for a lot of 6502-Commands).
An additional flag-byte is needed for every VIC20-RAM-byte.
- It's *not* faster than a normal interpreter:
Programs usually run about 4 to 5 times longer on the Atari.
This sounds very bad, but it is not. A lot of time is needed for
updating the display (about 40% of the time is needed when simulating
the colors on the Monochrom-Monitor) and for interrupts. Since I didn't
change a single bit in the kernel, the original routine for decoding
the key-matrix is running. On the other side, I had to encode the
key-events of the Atari to let that routine work correct.
I found out very early, that this is *not* the ultimate emulation. But I
continued working on it, until my favorite ROM-Modules of the VIC20, the
games 'AVENGERS' and 'STAR BATTLE', where running. As they were made in the
early days of the VIC20, their 'CPU'-usage is not too high and they can be
emulated nearly in real-time. Fortunatly they use the timers to 'sleep' and
not some strange loops.
Now I've got a problem: The Copyrights.
I wrote my program just for fun (although I though it's a great invention).
Of course, I would allow to copy it freely. But you can't do anything
without the copy of the VIC20-ROMS and some game-modules (you can get them
nearly as gifts, if you still find them in a store).
The question is:
- Am I allowed to distribute these files with my program ?
- If not: Am I allowed to copy these files at least to owners
of a VIC20, as they also could have transferred them
to the Atari on their own ?
Is there a 'yes'-answer anywhere ?
--
Helmut Hoenig, University of Kaiserslautern, Germany.
hoenig@informatik.uni-kl.de
--
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