Subject: Re: [stella] Thomas Jentzsch's PAL -> NTSC Conversions From: "Roger Williams" <mer02@xxxxxxxxxxxxx> Date: Fri, 8 Feb 2002 15:29:31 -0800 |
From: Eckhard Stolberg <Eckhard_Stolberg@xxxxxx> > Gas Hog is setting up a timer and keeps polling it constandly. > Indy 500 also does that, and I had problems with this game > too This absolutely will not work with video hardware that times from the end of VSYNC instead of the beginning. There will be variations in the timing which are not acceptable. The point of writing to WSYNC is that the end of the pulse is timed exactly to within one cycle. When you set up a loop you get at least a 15-cycle, and sometimes more, variation in the length of the pulse. It should not matter if you do logic within the vertical sync, but you must end it by writing WSYNC and waiting for the TIA to wake up the CPU. You don't even have to write all three of them, if you *know* your logic will take at least 2 scan lines and never more than 3 less STA WSYNC. Neither the NTSC nor PAL specification addresses whether hardware should trigger from the leading or trailing edge of VSYNC. Hardware which triggers from the leading edge will not care about sloppy trailing edge timing. Emulators too will vary in response depending on how they trigger their background video timing. --Roger Williams ---------------------------------------------------------------------------------------------- Archives (includes files) at http://www.biglist.com/lists/stella/archives/ Unsub & more at http://www.biglist.com/lists/stella/
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