Re: Asteroids hack

> > 1) More common. Go with the bigger target market...
> > 2) Already has all the analog sound hardware for Asteroids.
>
>Except there'll be many missing Deluxe sounds, and the Asteroids sounds
>can be approxmiated with the pokey that's on the Deluxe.

Nah... POKEY added to the daughtercard and muxed into the Asteroids audio
output summing circuit. (Much easier to add a POKEY than the analog sound
hardware. Well, for me at least!)

Still though, a combination technique would probably work for all
platforms-- some software patches to the DLX and LL code runs quite
comfortably on Asteroids hardware, and adding the POKEY gets you the DLX
sounds. For LL, the Pokey could recreate the varying thrust volumes...

> > I didn't want to try to recreate the analog sounds in hardware, and I
>didn't
> > want to hack the Asteroids Deluxe sound routines into LL or AST, so I
>liked
> > the Asteroids board. (I figure that the Asteroids thrust sound will be
>OK
> > in LL)
>
>Avoiding making software changes and doing it in hardware, eh? ;-)

Not as much as I've always really liked the smoothness of the Asteroids
"thrust" sound and I've never known a POKEY to get that same quality. Maybe
the POKEY output could be run through an external switchable filter or
something, but again, with fewer DLX boards out there Asteroids seemed like
a better hardware target to me.

[overclocking]
>Apparently the 65C02 has higher clock rate versions, too. I'm just looking
>for a source for them.

I don't think you'll find much anymore, but a few things to try:

1) WDC (but I don't think they sell chips anymore though)
2) Winbond (they have/had some 6502 compatible micro's for VCR's)
3) Mitsubishi (they had a 6502 varient microcontroller)
4) Conexant (the Rockwell modem chips like the C3900, L3900, L2900, etc were
just souped-up 6502's. We ran our high-end modems like the SupraSonic out
of an SRAM shadow memory [12ns] for full 40MHz 6502 compatible operation.
There were some changes to the instruction set, but if you're software
hacking anyway...)

> > [Overclocking] - If my memory serves, Asteroids runs essentially async
>from
> > the VSM.
>
>Completely async. It runs at exactly 45 redraws per second, which is
>around 22.2ms. It's actually computed in foreground code and the
>foreground code spins on a semaphore that's clocked off the NMI.
>
> > from the IRQ for the CPU?)-- if the game code has lots more cycles to do
> > stuff because of a faster CPU, all the better.
>
>Bingo. Sometimes the 1Mhz Asteroids would start flickering if there was
>lots of activity. As it's coded now, if the foreground code can't do it
>fast enough, it'll effectively "skip" drawing a frame.

Yeah, that seems to be a popular Atari technique. When I was doing my SNES
Asteroids clone I was in a weird "no frame skip" mood so if I ever didn't
make it out of the main loop before a redraw was due I did a BRK to just
kill things (thus making it obvious I missed a frame). I was OK up to 64
rocks and 15 bullets... That 16th bullet and I'd run out of MIPs...

Actually, someone might have suggested it already, but just buying up old
SNES consoles and sucking the CPU's out of those would be a good source of
65816 compatibles. They were speed-switchable (3.579MHz top end), but the
16 bit operations really helped out on the useful work that could be done.

-Clay
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Received on Tue May 8 15:07:49 2001