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From: ewhac@well.UUCP (Leo 'Bols Ewhac' Schwab)
Newsgroups: comp.sys.amiga
Subject: Re: Some thoughts and questions about the Ranger
Message-ID: <2725@well.UUCP>
Date: Sun, 8-Mar-87 04:33:51 EST
Article-I.D.: well.2725
Posted: Sun Mar  8 04:33:51 1987
Date-Received: Mon, 9-Mar-87 03:31:28 EST
References: <140@tahoma.UUCP> <158@rocky.STANFORD.EDU> <1513@cbmvax.cbmvax.cbm.UUCP>
Reply-To: ewhac@well.UUCP (Leo 'Bols Ewhac' Schwab)
Organization: Whole Earth 'Lectronic Link, Sausalito, CA
Lines: 54
Keywords: C64

In article <1513@cbmvax.cbmvax.cbm.UUCP> grr@cbmvax.UUCP (George Robbins) writes:
>In article <158@rocky.STANFORD.EDU> ali@rocky.UUCP (Ali Ozer) writes:
>
>>I imagine (with maybe a bit of clever programming) the Amiga could
>>emulate a C64 in full time (including to the smallest details including
>>sound, sprites, the different video modes, etc), in software only.
>
>It might be possible, however it is often a mistake to assume that the
>predecessor is so <generic negative> that you can emulate it in software
>in real time.  The 6502 is still a fast microprocessor,

	Really?  You think so?  The fastest I've ever seen those things
commercially is 2 MHz.  The C-64 runs at (slightly less than) 1 MHz.  After
moving to the 68K, the very THOUGHT of going back to the 6502 makes me gag.

>especially when
>munching 8-bit data, and the VIC chip is a pretty tricky little gadget
>by itself.
>
	It's tricky because of all the design barfs made on it.  Granted, if
you happen to have a scope and detailed knowledge of hardware, you can make
a bitmapped screen out of sprites with the thing (a friend of mine actually
did this).  But trying to do anything using the "obvious" approach generally
lands you into trouble.

>I've heard of a number of projects attempting to emulate machine x on
>machine y.  Generally, they get to the point where you can run k% of
>the programs at reasonable speed, but as you try to increase k, the
>emulation becomes slower and slower.  Perhaps I'll be surprised someday.

	Personally, I'm of the opinion that it should be more than possible
for a 7.14 MHz 68K to emulate a >1 MHz 6502 in software, generally.  After
all, the underlying processor architectures and philosophies are similar
(any data movement sets flags, rich addressing schemes, etc.).

	Tacking on the hardware emulation will definitely slow things down,
especially when accessing the VIC chip (should we emulate the 40 microsecond
CPU tromping every eight video lines?).  The CIA chips shouldn't be too
troublesome; we've got similar hardware in the Amiga.  How we'd do the sound
is anybody's guess.

	Sounds like a major commercial project.  Who wants to be first?

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