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Demos Amiga Demoscene Archive Forum / Coding / Difficult NTSC/ PAL question


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#1 - Posted: 10 Apr 2020 13:47 - Edited
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Hello All, I don't post often but be sure I always follow the work of everybody, and I must say it is a never ending amazement.

So , of course, I have a subtle hardware related problem, which brought me here:

I'm pretty close to modify one of my copper/blitter based demo so It would adapt every effects to the european PAL (50Hz, 256 scanlines) or NTSC video mode (60Hz, 200 scanlines)

... I've been using a little old code example "to check for Pal or NTSC" that does this:

move.w $dff000+vposr,d0
and.w #$7f00,d0 ; chip version bitmask
cmp.w #$2300,d0
beq.b .agaPal
cmp.w #$3300,d0
beq.b .agaNtsc

.. so on my UAE I have a ntsc checkbox that makes it work.
... But of course I also code and test on Pal Real Amiga 1200, and there is this boot issue: in the "2 mouse button startup", you can force NTSC or Pal at this level. But then my demo will run in 60Hz and the test always return Pal: no surprise, it is a "Chip version", it will not change in ntsc mode. So what I have to find is how to check the pal/ntsc information given at boot.

"problems you don't have with OS legal intuition screen demos"
#2 - Posted: 10 Apr 2020 13:51 - Edited
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Ho krabob, I also like your work, I think you should rather test the DisplayFlag in graphicsbase !
Tell me if it works !

/* Values for GfxBase->DisplayFlags */
#define NTSC 1
#define GENLOC 2
#define PAL 4
#define TODA_SAFE 8
#define REALLY_PAL 16 /* what is actual crystal frequency
(as opposed to what bootmenu set the agnus to)?
(V39) */
/* LightPen software could set this bit if the
* "lpen-with-interlace" fix put in for V39
* does not work. This is true of a number of
* Agnus chips.
* (V40).

... I realize suddenly because of these comments, that a PAL machine "switched to NTSC at boot" will always be different of a real NTSC machine, because of the CPU and bus speed (for A500: 68000 running at 7.15909 MHz (NTSC) or 7.09379 MHz (PAL)) Subtle-issime
#3 - Posted: 14 Aug 2020 14:46 - Edited
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Sorry please ignore / delete


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