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 20:32:13 -0500
I just tested a few minutes ago, and the screen does not roll anymore. I had
made the changes Dennis suggested, and also turned on VBLANK at line 261 as
Chris had recommended. So it is hard to say exactly what the problem was.
The reason I suspect it had something to do with writing 8 to VBLANK is
because an earlier version of the kernel did not roll, and there #$42 was
written to VBLANK (just like in"Our First Kernel"). The "lda #$42" line
before "sta VBLANK" was inadvertenly removed at some point.

I might do more experiments with writing 8 to VBLANK if there is enough

>From: "Dennis Debro" <dennis@xxxxxxxxxxxxxxx>
>Reply-To: stella@xxxxxxxxxxxxxxxxxx
>To: <stella@xxxxxxxxxxxxxxxxxx>
>Subject: RE: [stella] 262 scanline kernel is rolling
>Date: Sat, 26 Mar 2005 14:49:35 -0500
>Hi there,
> > Right now you're writing 0 at the start of vertical blank
> > and 8 at the start of overscan.
>That is strange. As Thomas said, D1 of VBLANK only controls the TIA output.
>At least as documented by the programming manual. So writing 8 to the
>register is essentially the same as writing 0 (i.e. enabling TIA output).
>I don't have my hardware setup at the moment to play with this. Was this
>truly the problem? What happens if you used other values or ignored VBLANK
>altogether? By the values you were entering this should have been
>Are there other bits used by VBLANK that we don't know about?
>Take care,

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