RE: 6502 Recompiled

Just curious, what product did you release (provided it was game related)?

Ed

-----Original Message-----
From: owner-vectorlist@vectorlist.org
[mailto:owner-vectorlist@vectorlist.org] On Behalf Of Neil Bradley
Sent: Saturday, October 16, 2004 1:45 PM
To: vectorlist@vectorlist.org
Subject: Re: VECTOR: 6502 Recompiled

> This decompiling/recompiling may not be as easy as it sounds. I listened
> to a talk by old Atari arcade programmers, and the did a lot of tricky
> stuff to keep the boards from being bootlegged. One of them (I think
> it was Owen Rubin.. programmer of Space Duel) said that he things like
> noticing that " A" was the same as a JMP instruction in 6502, and so he
> would jump into the memory containing the atari copyright message and
> depend on it jumping back out again.. but I doubt a recompiled version
> would do the right thing.

Aha - but it does! It'd do something like:

        goto label1
label2:
        a=xxx;
label1:

I had to account for that type of thing when I did the Ms Pacman
recompilation.

> Either it'd be jumping into the original
> 6502 code, or it'd be compiling the static strings and that means that
> it wouldn't work properly.

But it ends up back in "good" code since eventually the two paths would
sync back up again.

> Quite frankly, getting a 60Mhz embedded processor to emulate a 1Mhz 6502
> shouldn't be that difficult.

It isn't difficult (in fact I worked on a product that does exactly this).

> The virtualized hardware (like the AVG) will
> be where you need to optimize.. not the main code.

Well, having worked on a released product with this concept, I'll disagree
with you there. Emulation is a considerable amount of CPU time on lower
end CPUs (in our case an Atmel 66Mhz ARM7TMDI core) - enough that it's
prohibitive when you start getting in to multiple processors, and if the
graphics are intensive, having more time left over to do graphics can
either make or break an emulation. The less time the CPU is doing
emulation, the more time it can spend doing the graphics, which makes more
complicated games plausible on lower end hardware.

-->Neil

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---
Neil Bradley             "The true axis of evil in America is the brilliance
of
Synthcom Systems, Inc.    our marketing combined with the stupidity of our
                          people.." -  Bill Maher
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