Subject: Re: [stella] WSYNC and RESPx questions From: Eckhard Stolberg <Eckhard_Stolberg@xxxxxxxxxxxxxxxxxxxxx> Date: Sat, 21 Aug 1999 17:19:41 +0200 |
At 10:55 21.08.99 +0200, you wrote: >I have no access to hardware, therefore i'm testing >everything on different emulators. They all allow WSYNC to >start at cylce 74, but i'm not shure if this emulation is >correct. IIRC if you start the WSYNC after cycle 72, you'll get an extra scanline. >My second question is: what is the earliest usefull cycle >for RESPx? They all are usefull depending on where you want to position the object. Hitting RESxx at any cycle before 22 will have the same effect as hitting it at cycle 22 though. But this means that you have more possibilities to position objects on the left side of the screen, which can be usefull if your display kernal is very timing sensitive. >If you look at riveraid.asm again, you find a special >routine for players on the very left side. The RESP1 >doesn't end at cycle 23, which would be correct in relation >to the other possible values. It ends at cycle 25 and an >extra HMOVE for 6 pixel to the left is done to correct >this. I've no explanation why this is done that way, maybe That's because of the HMOVE command right after the fist WSYNC. If you access RESxx or HMxx within 24 cycles after a HMOVE command, you might get different positions for the objects than normal. Z26 emulates this effect except for most of the variations on the Cosmic Ark starfield effect, which works by doing just this. Ciao, Eckhard Stolberg -- Archives (includes files) at http://www.biglist.com/lists/stella/archives/ Unsub & more at http://www.biglist.com/lists/stella/
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