Re: Asteroids hack

> > Clay picked the Asteroids board as the basis for his project.
>
>And I picked the Asteroids Deluxe boardset because it's capable of doing
>everything the other two boards can do. The Asteroids board lacks a Pokey,
>so getting Deluxe to run on it would require far more hardware to make it
>run.

Hi all...

I've been off in my own little world the last few weeks, so I'm *way* behind
in vector-list email. ;-)

Anyway, yes-- I chose Asteroids as the base for my kit for two main reasons:

  1) More common. Go with the bigger target market...
  2) Already has all the analog sound hardware for Asteroids.

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)

Here's a few misc. thoughts about the past threads I just read. In no
particular order:

[Overclocking] - I'd think that it's possible, but I suspect you'll need to
isolate the CPU memory to make it work (basically fast EPROM and SRAM with
the CPU for program code and data). Might have to make it software
switchable to allow the CPU to shift gears to load the VG RAM unless you
want to replace that and the VG EPROM with faster stuff too.

[Overclocking] - Ed and I talked about this a long time and figured the best
way to do it would be to roll something like http://www.free-ip.com/6502/
into a Virtex or Spartan FPGA. Plenty fast then. :-) The lack of BCD would
be a problem for Atari stuff IIRC, so that would have to get fixed.

[Overclocking] - If my memory serves, Asteroids runs essentially async from
the VSM. Every 30mS (or something) the VSM does a redraws (maybe triggered
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. As long as the VSM can still
get at the VRAM and VGROM all should be well. (Vector Breakout uses a
similar technique-- the "main loop" actually runs around 4-5 times
completely through in between every screen refresh. That allows me to do
what amounts to "sub-sampling" on the ball position, so even when the ball
speeds up (moves more per frame) the hit accuracy on the bricks stays
constant.

[Old game enhancement kits] - Those are cool! They might look pretty
expensive by today's standards ($75 for a one byte patch for faster firing),
but back then that kind of stuff was much harder to do! EPROM readers,
burners, and development tools were *way* different then (and horribly
expensive), so even something simple by today's standards was a big task.
(In the pre-MAME days when I did my hacks to Astro Blaster for faster gun
cooling and slower fuel consumption I had to read the ROMs, disassemble the
code, and then sit there with my EPROM emulator and a little home-made
"trigger" widget and a logic analyzer to track down what different things
did in the code. Took about two evenings of work to get both patches in.
If I had to burn EPROMs every time, and didn't have the logic analyzer
(~$10K new when Astro Blaster came out!) it would have taken a *long*
time... By contrast, with MAME now those same hacks would take about 8
minutes. ;-)

I'd best get back to soldering...

-Clay
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Received on Sat May 5 14:33:52 2001