Re: [stella] 262 scanline kernel is rolling

Subject: Re: [stella] 262 scanline kernel is rolling
From: "Aaron" <stella-receiver@xxxxxxxxxxxxxxxxx>
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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