Subject: Re: [stella] Don't say you weren't warned.... From: Pete Holland <petehollandjr@xxxxxxxxx> Date: Sun, 15 Aug 1999 11:07:51 -0700 (PDT) |
--- Erik Mooney <emooney@xxxxxxxxxxxxxxxx> wrote: > It starts at RAM location $FF (also accessible via > $1FF, $20FF, $21FF, $40FF, $41FF, etc) and expands > downward. $FF is zero page and fastest, right? > RAM is located from $80 to $FF, also accessible via > $180 through $1FF, $2080 through $20FF, $2180 through > $21FF, etc. Same as above? > (I know the Supercharger breaks most of what I just > said, but let's not confuse him... :) Thanks. I'm confused enough as is. ;-) > Right. Feel free to look through some source code... > my own INV includes a lot of this stuff; looking at > the source might help with the syntax. Umm...where can I find this code of INV? Is it at The Dig? Is it commented out, too? > It counts time for you so your code doesn't have to > do it. By far the most common use is to, immediately > after VSYNC, set TIM64T so that it will expire 37 > scanlines later. Then you do all your calculation > code, and then just watch the timer till it expires, > then you know it's the right time to start drawing > the screen. This way, you don't have to make sure > you catch every one of the 37 WSYNCs while doing your > game calculation. Just to make sure I'm clear on this: would TIM64T be set for 37, or the number of color clocks, or what? And fits into the program how? I set it for whatever number, it automatically counts down and I check for when it hits 0, then start drawing the screen? Is TIM64T just a number to check and I still need the WSYNC in the overscan period, or is that handled by the command? Also, would I store at TIM64T the number for the overscan AFTER the frame, since it would be when that expires that I VSYNC three times, then just reset the number for the 37 before the next frame? > WSYNC is a strobe register; doing STA WSYNC doesn't > actually shut anything on or off. It's a signal to > the TIA to keep the CPU in a halt state until the > current scanline finishes. So that makes it my responsibility to tell the program to switch it on and off with a specific number that turns that bit on or off, right? > The LDA sets the zero flag (that BNE tests) without > need for a compare. Whoa, no kidding. Then which branch commands need a compare command first, and which can just be done without it? I'll get the hang of this yet.... _________________________________________________________ Do You Yahoo!? Get your free @yahoo.com address at http://mail.yahoo.com -- Archives (includes files) at http://www.biglist.com/lists/stella/archives/ Unsub & more at http://www.biglist.com/lists/stella/
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