Subject: Re: [stella] Weird Loop... From: Manuel Polik <manuel.polik@xxxxxxxxxxx> Date: Thu, 07 Dec 2000 16:13:39 +0100 |
Thomas Jentzsch wrote: > Manuel Polik wrote: > > In Starmaster I found this loop: > > > > LDX #$18 > > Loop: STA WSYNC > > LDA VSYNC > > NOP > > NOP > > NOP > > NOP > > DEX > > BPL Loop > [snip] > > Now, I've no clue, what the LDA VSYNC & the NOPs are for... > > Can someone explain that to me? > LDA VSYNC is a problem of DiStella, it doesn't show read accesses correct (should be LDA CXM0P). Try the trace-mode of z26, there you will find the right code and some more valuable information. > The NOPs are used for the following routine, where some player positioning happens (I think, they could have moved those NOPs behind the loop). Aha! Thanks for the help, now I got it: The LDA CXM0P is really for nothing, just an instruction taking uneven (3) cycles. I found out that the subroutine which does the player positioning must start after 15 cycles and you can't do that with just DEX + BPL + x * NOP , they're all taking even cycles... Greetings, Manuel -- Archives (includes files) at http://www.biglist.com/lists/stella/archives/ Unsub & more at http://www.biglist.com/lists/stella/
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