>So far I'm no where near needing 4K. Why can't I go all the way to 8K
>minus TIA and RIOT address ranges without any bankswitching? Exactly
>(in 25 words or less), what's that all about? There are lots of details
The 2600's addressing system allows for 8192 bytes. The cartridge
only has access to 4096 of them. The bit on the address bus that
controls whether the address is $0xxx or $1xxx controls whether
access is directed inside the machine or out into the cartridge
port. Consequently there is 3k of address space inside the 2600
that is a complete and total wasteland.
>> I'd be surprised if either of them used actual applied geometry and
>> physics. The best example of physics I can think of is Space War,
>> and if my tests are right, things like the inverse square law of
>> gravity apply. It's not like Gravitar. To be honest, the more I
>> play Gravitar, the more I'm disappointed in the physics it uses,
>> it being 8K and Space War being 2K and all that.
>
>The physics are kinda secondary, and I'd settle for any at all. The
>real thing is switching from hard-coded horizon/distance events to
>elegant equations for everything.
Math is a bitch and a half on the 6502 to begin with, but on the 2600
it has to be fast. How about tables? Defender uses tables to multiply
by 40 (though I haven't ascertained exactly why it needs to do that
so often, yet).
Going back to Defender, its process for dividing by 15 for the horizontal
positioning loop is simple. Subtract by 15 until you run out of 15s.
But too many iterations of this loop, and you'll spill over into the
next scanline causing the screen to shift downward depending on
how far objects are to the right. Defender's solution was to see if
the number was more than 82, and if it was, subtract 75. I don't
know why it checked for 82 when it wanted 75, but I'll find out.
>Now that there are a new batch of people chatting about this stuff, I'm
>starting to feel like doing it more (at the expense of other things that
>are suddenly losing their appeal?). The other thing 2600 programming
>definitely takes: company. It can be a very lonely endeavor.
I'm probably the only human being in a 600 mile radius who understands
anything about this particular topic. Certainly without the list, or
at least Usenet, I would have seen little reason to continue.
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