Re: [stella] 6 Digit Routine Cont.

Subject: Re: [stella] 6 Digit Routine Cont.
From: Thomas Jentzsch <tjentzsch@xxxxxx>
Date: Wed, 10 Sep 2003 12:14:53 +0200
Chris Larkin wrote:
> I would assume the entire graphic
> data has to fit on one page to keep cycle counts accurate?

Yup! It's *very* important to avoid page penalties here!

>  ^ How can this always produce the same amount of cycles?

Don't worry, I have changed that code so often, that I didn't 
adjusted the comments always. :-)

>      ldy     MsgTab,x            ; 4
>  ^??????? Totally lost here |Load height of graphic?

No, offset into a table that contains the pointers to the various 

>      lda     LetterPtrTab,y      ; 4
>      sta     digitPtr            ; 3
>  ^LetterPtrTab,Y = Address of first 8x8 Graphic?

Yup! (though the height doesn't matter)

>      sta     digitPtr+2          ; 3
>  ^digitPtr is in Zero Page... So the graphic data is loaded into 

Nono! Not the *data* only the *pointer* to the data. 

>  ^ I have to get this exact cycle count?

Don't worry again. The code is heavily optimized and therefore I 
am entering it at various positions. Just make sure that the 
following 'dey' ends at cylce 61.

>      sty     GRP0
>      sty     GRP1
>      sty     GRP0
>  ^Why is GRP0 cleared twice?

Because both players are VDELed. 

The first write to GRP0 clears the shadow register of GRP0. Then 
sty GRP1 clears the shadow register of GRP1 and copies the shadow 
register of GRP0 into the visible register. The final sty GRP0 
copies the shadow register of GRP1 into the visible one.

>  So assuming my graphics data is as follows, How do I get this 
>  subroutine to draw it correctly?
>      ORG $1200
>  Graphic0    .byte $00,$00,$00,$00,$00,$00,$00,$00
>  Graphic1    .byte $00,$00,$00,$00,$00,$00,$00,$00
>  Graphic2    .byte $00,$00,$00,$00,$00,$00,$00,$00
>  Graphic3    .byte $00,$00,$00,$00,$00,$00,$00,$00
>  Graphic4    .byte $00,$00,$00,$00,$00,$00,$00,$00
>  Graphic5    .byte $00,$00,$00,$00,$00,$00,$00,$00

Do something like this six times:
  lda #<Graphic0
  sta digitPtr
  lda #>Graphic0
  sta digitPtr+1

Where are my $10,000? ;-)

Have fun!

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