Hey:
Much thanks. I can't believe I was having such problems seeing that.
I guess having a second pair of eyes look at things is good. With your
suggestions I was able to clean up the main loop considerably.
Thanks again.
gene
On Sat, 18 Sep 1999, Eckhard Stolberg wrote:
> At 12:35 17.09.99 -0700, you wrote:
>
> >One thing I'm having problems with is why the board is so far to the
> >left side of the screen. If I add one more NOP to delay it, I go over
> >the scan line limit and break the display. Can anyone give a
> >suggestion on how to center the display?
>
> The current routine to display one scanline takes 73 cycles from
> one WSYNC to the next. If you add another NOP, it would be 75
> cycles and cycle 75 is too late for WSYNC to catch the end of
> the current scanline.
>
> What you could do is add a 3 cycle instruction, like STA $3f, to
> the NOPs. Then have the DEX/BNE ... thing loop to the instruction
> after the WSYNC at scanloop. This way you would be doing 76 cycles
> per scanline which fills the whole scanline, so that the next time
> through scanloop everything would be executed at the same cycle
> in the scanline as before. This would shift the display 9 pixels to
> the right.
>
> Another thing that you could do is taking out the DEX/BNE ... at
> the end of the loop and put in a DEX/BEQ EXITLOOP before the NOPs.
> That would take 5 cycles from behind the display and put 4 cycles
> in front of the display which would shift the display 12 pixels to
> the right.
>
> BTW: Your demo does only 251 scanlines per frame. You should change
> that to 262 lines per frame, just to make sure you stay in Atari's
> specification.
>
>
> Ciao, Eckhard Stolberg
>
>
>
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