[stella] cosmic ark stars missile 1

[Darrell Spice, Jr.]

I used M1 to generate the stars in Stay Frosty.

	ldx #$70
	stx HMM1
	sta WSYNC
	sta HMOVE     ;  3
	SLEEP 16      ; 16 19
	dex           ;  2 21
	stx HMM1      ;  3 24 ; this confuses the TIA and generates stars :-)

values are $7x and $6x for the 2 HMM1 hits.


On Jan 15, 2008, at 7:17 AM, Andrew Davie wrote:

> I don't understand the magic behind cosmic ark stars, but I am  
> using it
> successfully for Boulder Dash to give the extra-life shimmer.   
> However, the
> code I use is using missile 0 and I really want to use missile 1.   
> But when
> I change things from missile 0 to missile 1, I no longer get  
> 'stars';  just
> 'stripes'.  In other words the effect doesn't work.  I'm pretty  
> sure it's to
> do with the magic numbers in the following code.  I just don't know  
> what
> magic numbers to use for M1 (or for ball).  Can anyone help?
>
>                 jsr rndm
>                 and #7
>                 clc
>                 adc #4
>
>                 TAY
>          ;       STA     WSYNC
> .r22             DEY
>                 BPL     .r22
>                 STA     RESM0
>                 LDA     #$70            ;this value is important  
> for the
> effect
>                 STA     HMM0
>
>                 STA     WSYNC
>                 STA     HMOVE
>                 JSR     Trick2           ;waste 18 cycles and load  
> move
> value
>                 STA     HMM0            ;this is the tricky part
>
>
>                 LDA     #$02            ;turn missile0 on
>                 sta WSYNC                       ; 3
>                 STA     ENAM0
>
>                 rts
>
> Trick2:          NOP                     ;the tricky subroutine
>                 NOP
>                 LDA     #$60
>                 RTS
>
>
> The above gives a reasonable random effect for me.  If I change the  
> lda #$60
> then it stops working.  If I change to missile 1, it stops working.
>
> Could someone please analyse this and/or suggest the correct values?
>
> Thanks
> A
>
>
>
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Darrell Spice, Jr.
darrell.spice.jr at spiceware.org



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