Re: [stella] Megacart Specs

Subject: Re: [stella] Megacart Specs
From: Chris Wilkson <cwilkson@xxxxxxxxxxxxx>
Date: Sun, 12 Apr 1998 18:26:24 -0700 (PDT)
> On Sun, 12 Apr 1998, Chris Wilkson wrote:
> > RAM (see below).  You could use 3K blocks for ROM and permently map RAM
> > into the remaining 1K, but that either wastes ROM space or the decoding
> > gets nasty from a hardware point of view.
> Small games, okay, but it just seems that if you've written a game that
> uses the full 128K of ROM code (a huge kernel and tons of date) and you
> have only 1K linear ROM available at a time that the programmer is going
> to have to bank switch constantly to get anything done.  The percetage of
> bankswitching code to useful code is starting to get really wasteful.
> After you load the 1K chunks, can you run a program linearly across the
> loaded banks without bit-twiddling?  If so, then it's not too bad because
> you could write code as de-facto 3K chunks and then swap three banks in
> and out that way but I don't know why a program would need to be broken
> down into even small chunks. 

Yes, as far as the 2600 is concerned it simply has a 4K chunk of memory at
at a given time...except when there is RAM mapped into a slot.  Then you lose
512 bytes because of using A9 for a read/write line.  If you wanted to, you
could even execute code from RAM and just keep going linearly into a ROM
block.  But you can't do the reverse...the write port for RAM is in the
lower 512 bytes of the slot.  If you try to execute linearly into a RAM
block, you'll overwrite the RAM!

the code.

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