Subject: Re: [stella] why -68? From: "John Saeger" <john@xxxxxxxxxxx> Date: Tue, 6 Nov 2001 08:49:41 -0800 |
You should thank Eckhard too. He's been doing most of the work for the last couple of years. In any case, we start counting TIA cycles at -68 because that's how PCAE does it. We wanted to make it easy to compare results between z26 and PCAE. When working on an emu, it's very handy to be able to compare with other ones. But this way TIA starts drawing at cycle 0. Yes there are 228 cycles per scanline. 160 - (-68) = 228. But the last cycle you'll ever see is 157. 160 would put it at the beginning of the next scanline. At least that's what I think it should do. Funny, even to this day we're still having discussions about where a scanline should end and the next one should begin. It has to do with the worm war demo that was posted a while back. In z26 1.51 it doesn't jitter any more. Some of us think it should still be jittering, and some of us aren't so sure. Stay tuned. And TIA clock = 3*CPU clock. 228 = 3*76. John ----- Original Message ----- From: "ben" <ben@xxxxxxxx> > z26 is awesome btw :) Thanks John > > Anyways, I have a question regarding its cycle output. Why does the TIA > clock start at -68 and occupy 236 clocks (-68 to 157)? isnt it supposed to > be 228? > > ( 0 2 0 -68) ( 97 97 96 96 96) nvbdIzc 00 60 00 fd f5c2: d0 fb > bne f5bf > .... > ( 0 2 75 157) ( 97 97 96 96 96) nvbdIzc 00 68 00 fd f5bf: e8 > inx > .... > etc > .... > > Does this mean that the TIA clock is different to the 6502? I am using > 3584160/3 Hz (228*262*60/3) for the CPU, which gives 76 cycles per > scanline. What should the TIA clock be? (236*262*60) 3709920Hz? > > cheers > > Ben > > > -------------------------------------------------------------------------- -------------------- > Archives (includes files) at http://www.biglist.com/lists/stella/archives/ > Unsub & more at http://www.biglist.com/lists/stella/ > > ---------------------------------------------------------------------------------------------- Archives (includes files) at http://www.biglist.com/lists/stella/archives/ Unsub & more at http://www.biglist.com/lists/stella/
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