Subject: Re: [stella] Supercharger RAM question From: Eckhard Stolberg <Eckhard_Stolberg@xxxxxxxxxxxxxxxxxxxxx> Date: Sat, 14 Mar 1998 15:51:57 +0100 |
At 11:59 13.03.98 -0500, you wrote: >One SC question: Is there any part of the SC that I need to worry about >that is _not_ RAM? I'm not anywhere close to messing with the SC, but it >has in the past sounded like you could rewrite part of your scan line >routine (for example) during overscan with the SC. That is just about >perfect for achieving special effects for this game. I was thinking >about writing a program that actually had commands in the Atari's RAM, >just to see if that would work... This is pretty much what writing code >for the SC would be like, correct? (knowing, of course, that I'd have >TONS more RAM!) My Domino program changes it's display code in SC RAM, so it is possible. Address $FFF8 contains the control byte for the SC. Any writes to it would switch RAM banks or turn on and off SC writing. Therefore you can't use it to store data. Accesses to addresses between $F000 and $F0FF would cause SC writes. You can't read from, write to or run code in this page, when SC writing is enabled, or your program might crash, because your code got changed accidentely. If you don't want to waste these 256 bytes, you can put some code or data there, that is not needed for writing. Then you can enable SC writing for the routines, where you need it, and disable it afterwards. All other addresses can be used to write too. But you should remember, that SC writes take quite some cycles and if you also have to use complicated calculations to find the correct address to write to in your display code, there is not that much time for doing many writes during Vblank. I think it would be better, if you would start with a simple display kernal first and add effects like this later. BTW, the 'prizes' in Jumpman are supposed to be bombs. :-) Ciao, Eckhard Stolberg -- Archives (includes files) at http://www.biglist.com/lists/stella/archives/ Unsub & more at http://www.biglist.com/lists/stella/stella.html Don't post pirate BINs to Stellalist. Be a programmer, not a pirate. Write the best game, win framed autographs of famous Atari alumni!!
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