Subject: [stella] nop and wrap around From: Mark De Smet <desmet@xxxxxxxxxxxx> Date: Tue, 12 Jan 1999 17:35:11 -0600 (CST) |
Now that I've finished my last project, I've been thinking about my newest plans, and was wondering somethings.(The last one was that RAM-cart that was programable with a dos copy command. Finally got it all working) My newest will be a small embedded system connected to the atari. It will have an LCD screen that allows the user to select a game from it's large ROM(and simultaniously display instructions while playing), load one from a pc via serial, load one from actual cart(and send to pc), setup bankswitching, and any other number of things that I can dream up along the way. But anyway, what I was trying to figure out. My original thoughts to run it would be that my system would be able to switch on and off the power to the VCS so that once a game was choosen, it would power cycle the VCS to play the new game. But while working I came across an idea. What if my system just swaped the rom while that last game was running? What I was thinking is swapping it to a rom that is all nop's, and allowing the VCS to run those nops until it got to a certain address(startup vector?) which would cause some of my hardware to switch to the new game. Or perhaps to a dummy program which would just display some text, or maybe a screen saver of some sort until the user selects the next game. It's kinda like a bankswitch without having a software call to do it. Will this work? Is there a common startup address(as in, is there a location in memory where the 6507 fetches the very first instruction upon startup?)? What is it? Will the program counter in the 6507 wrap around from the max to the minimum address? Anybody have any ideas of how else to be able to get from a game running to another one when you have no control over how either program was written or where in it's execution it is? Mark De Smet -- Archives (includes files) at http://www.biglist.com/lists/stella/archives/ Unsub & more at http://www.biglist.com/lists/stella/
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