[stella] Cosmic Ark scanline pixel doubling

Subject: [stella] Cosmic Ark scanline pixel doubling
From: Adam Wozniak <adam@xxxxxxxxxxxxxxxx>
Date: Fri, 11 Mar 2005 20:15:34 -0500
Hash: SHA1

On Fri, 11 Mar 2005, Eckhard Stolberg wrote:
> BTW, since you are studying the TIA schematics, did you already
> have a look at the setup logic for the movable-object output?
> I'm wondering if there might be something in there that could
> be messed up by a HMOVE pulse happening during this setup
> procedure, because there is some pixel doubling and deleting
> in some scanlines during the Cosmic Ark starfield effect that
> I can't explain.

I wish I could say that staring at these schematics for hours on end has
made me the sort of minor diety that could answer this question instantly.

I assume you're refering to this post from back in 1997?

I have to honestly say I don't know what's going on here.  I just
completed a testable version of my tia.vhd for the fpga2600 project last
night, and will begin designing hardware for testing "soon".

I think my version gets the various NUSIZ tricks right.  These just sort
of fall out naturally.  But I'm at a bit of a loss for the HMOVE tricks.
I've tried walking through this logic a few times before, but I get lost
in the intricacies of exactly what happens when HMOVE gets hit before
the required setup time has occurred.

(Hrm, just found a bug in my HMOVE handling.  Off to fix it...)

- -- 
adam@xxxxxxxxxxxxxxxx        http://cuddlepuddle.org/~adam
KG6GZR                       http://cuddlepuddle.org/~adam/resume.html

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