Re: [stella] Submitted for your (dis)approval: griddemo

Subject: Re: [stella] Submitted for your (dis)approval: griddemo
From: Erik Mooney <emooney@xxxxxxxxxxxxxxxx>
Date: Wed, 17 Nov 1999 15:36:51 -0500
>One thing I'm having problems with is why the board is so far to the
>left side of the screen.  If I add one more NOP to delay it, I go over
>the scan line limit and break the display.  Can anyone give a
>suggestion on how to center the display? 

Let's see what you're doing at the end of each scanline, unspaghettiing
your jumps:

>        LDA #$00 
>        STA COLUBK 
>        JMP rdlreturn
>rdlreturn      ; ramdrawline jmps here when it is done
>        DEX
>        BNE scanloop
>        STA WSYNC

After the final color change to black is done, you have 3 + 2 + 3 + 3 = 11
cycles of instructions, which take 33 color clock pixels, so you won't be
able to display anything in the rightmost 33 pixels of the screen.  Lower
that 11 number to be able to display things farther right.

I'd suggest moving the DEX / BNE to within the RAM loop, so you jump to
RAM, do your 16 lines or whatever all within RAM, then jump out.  Instead
of jumping in and out of RAM on every scanline, which takes lots of extra

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