Re: [stella] 262 scanline kernel is rolling

Subject: Re: [stella] 262 scanline kernel is rolling
From: "Zach M" <zach_in_sac@xxxxxxxxxxx>
Date: Sat, 26 Mar 2005 01:17:47 -0500
Thanks Aaron. I believe that VBLANK was the problem in my kernel.  One thing 
I'm confused about though:  Should VBLANK be set at the start or the end of 
overscan? I just used z26 to trace the code of Pacman and Outlaw, and it 
appears they set VBLANK at scanline #263.

>From: "Aaron" <stella-receiver@xxxxxxxxxxxxxxxxx>
>Reply-To: stella@xxxxxxxxxxxxxxxxxx
>To: stella@xxxxxxxxxxxxxxxxxx
>Subject: Re: [stella] 262 scanline kernel is rolling
>Date: Fri, 25 Mar 2005 21:24:45 -0500
>Zach M said:
> > Hello all, my first homebrew kernel looks good in emulators, and z26
> > reports
> > that it displays 262 scanlines, but when I test on a TV the image rolls
> > slowly, almost like a scrolling background in a Xevious-type game.
>It doesn't look like you're using VBLANK (the TIA register) correctly.
>You should turn it off (write 0) at the start of the visible screen, then
>turn it on (write 2) at the start of overscan and leave it on throughout
>vertical blank.  Right now you're writing 0 at the start of vertical blank
>and 8 at the start of overscan.
>I'm in a similar situation with my game (works fine in emulators, rolls
>badly on a real machine) and this was one of the first things I checked...
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