Re: [stella] Reading the Booster Grip

Subject: Re: [stella] Reading the Booster Grip
From: tjentzsch@xxxxxx
Date: Wed, 13 Feb 2002 11:50:42 +0100
I wrote:
> I'll disassemble Omega Race soon...

Ok, here is what I found (this code is placed just before the begin of VSYNC):
    lda    SWCHA      
    and    #$cc    	; clear up and down bits
    ldy    INPT0         
    bpl    Lf25b          
    ora    #$10         ; enable up bit
    ldy    INPT1        
    bmi    Lf263        
    ldy    INPT4        ; fire button is also an option here
    bmi    Lf265        
    ora    #$20         ; enable down bit

...about the same code is repeated for the other joystick port depending on P1 difficulty

Then directly follows the VSYNC block (with a bit unusual timers):
    lda    #$82           
    sta    WSYNC     
    sta    VSYNC      
    sta    VBLANK    ; sets bits 1 and 7
    lda    $0285        
    lda    #$2a          
    sta    $029d        ; about the same as TIM8T
    lda    $0285        
    bpl    Lf29a         ; wait for timer (5 scan lines)
    lda    #$00          
    sta    WSYNC    
    sta    VSYNC     

And at the end of VBLANK the bits 1 and 7 are cleared again.

I can't see any new informations in this code, perhaps others will know better.

Attached is a DiStella configuration file for the last 4K block, so you can disassemble it yourself.

Have fun!
Thomas Jentzsch         | *** Every bit is sacred ! ***
tjentzsch at web dot de |

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Attachment: omega3.cfg
Description: Binary data

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