[atari7800] SpaceWar! 7800 update

Just to say that I haven't completely abandoned this project; it's simply a
question of free time and the multitude of projects I have on the go.

Anyway, one of the objectives of SpaceWar! 7800 was to see if it was
possible to cram the game into 4K with the intention of releasing it using a
standard 2600 4K cartridge (instead of having to create a 7800 PCB).

Well, I was able to accomplish quite a bit in just 4K.  (Not as much as many
would have liked mind you.)  But a test cart done by Jarett Waite of PackRat
Video Games failed on startup.  Not having any easy way to figure out where
the problem was, I put SpaceWar! 7800 on the back burner this spring.

Well, I finally took the time to do a little testing with my CC2.
7800_4K+78BIOS worked, 4K+78BIOS failed, but 4K+78QUICK worked.  Hmm...
maybe the BIOS is doing a test which is kicking it into 2600 mode.  A scan
of the Keith Henrickson/Daniel Boris disassembly confirmed it - starting at
$F8E7 the BIOS runs a full RAM test which fails because the 2600 cart is
shadowed at $1800-$1F00.

Oh well.  I guess this means I don't have any reason to limit myself to 4K.
Hmm, what will I do with all of that address space?  Gotta work on that
Expensive Planetarium and maybe convert my graphics to 320B...

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