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xIII
Registered: Nov 2008
Posts: 210 |
Stable Raster routine
A long time ago I coded a small routine which shows some rasterbars moving on the screen (Transparent Rasterbars). I got some help from my mates in WOW with this stable raster routine.
I know that the NOPs are there for cycle timing but I don't understand how it works :(
Can someone explain me how this works?
;--------------------------------------------------
; stable raster routine ?
;--------------------------------------------------
irq INC $D019 ; 6 cycles
LDY #$19 ; 2 cycles
INY ; 2 cycles
INY ; 2 cycles
STY $D011 ; 4 cycles
NOP ; 2 cycles
NOP ; 2 cycles
NOP ; 2 cycles
NOP ; 2 cycles
NOP ; 2 cycles
NOP ; 2 cycles
NOP ; 2 cycles
NOP ; 2 cycles
NOP ; 2 cycles
LDY #$00 ; 2 cycles
jump01 LDX #$F8 ; 2 cycles
LDA rastertable,Y ; 4+ cycles
jump03 STA $D020 ; 4 cycles
STA $D021 ; 4 cycles
INY ; 2 cycles
INX ; 2 cycles
BEQ jump01 ; 2++ cycles
NOP ; 2 cycles
NOP ; 2 cycles
NOP ; 2 cycles
NOP ; 2 cycles
NOP ; 2 cycles
NOP ; 2 cycles
NOP ; 2 cycles
NOP ; 2 cycles
NOP ; 2 cycles
NOP ; 2 cycles
NOP ; 2 cycles
NOP ; 2 cycles
NOP ; 2 cycles
NOP ; 2 cycles
NOP ; 2 cycles
NOP ; 2 cycles
LDA rastertable,Y ; 4+ cycles
CPY #$80 ; 2 cycles
BCS clearrastertbl ; 2++ cycles
NOP ; 2 cycles
NOP ; 2 cycles
CLC ; 2 cycles
BCC jump03 ; 2++ cycles
; ---------------
; 94-102 cycles |
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Dr.j
Registered: Feb 2003
Posts: 277 |
@xIII/WOW: for simple rasterbars effect you don't need stable rasters. you can use delay table or better
a compact raster routine which take 63 cycles for
normal line/21 cycles for bad line. good luck |
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xIII
Registered: Nov 2008
Posts: 210 |
Dr J.: I usually use a delay table, at least I understand how that works ;)
Thanks everyone for the replies and especially for the links and the PDF ! |
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HCL
Registered: Feb 2003
Posts: 728 |
Checkout Uncensored for a stable raster routine.. even rotating :) Haha, i just couldn't resist :P. |
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Pantaloon
Registered: Aug 2003
Posts: 124 |
hcl, haha |
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Smasher
Registered: Feb 2003
Posts: 520 |
that part with rotating rasters caused the biggest "WOOOOOW!" in the whole democompo! :) (ok, offtopic & I dont care) |
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chatGPZ
Registered: Dec 2001
Posts: 11386 |
despite that i wouldnt call this drunken mess exactly stable at all! =P |
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