[stella] cosmic ark stars missile 1

[Andrew Davie]

Strange.  If I use this code I don't get stars.  If I change it to missile 0
I do get stars.  Is Stella (the emulator) confirmed to work with the star
effect with missile 1? I don't have hardware setup to test this.

Cheers

A



 

  _____  

From: stella-bounces at atari2600.org [mailto:stella-bounces at atari2600.org] On
Behalf Of Darrell Spice, Jr.
Sent: Wednesday, January 16, 2008 2:15 AM
To: Atari 2600 programming list
Subject: Re: [stella] cosmic ark stars missile 1

 

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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