RE: [stella] Space Instigators - Final Version (?)

Subject: RE: [stella] Space Instigators - Final Version (?)
From: Christopher Tumber <christophertumber@xxxxxxxxxx>
Date: Sat, 19 Oct 2002 21:27:15 -0400
Nicolás wrote:

>I´ve tested SP18 with PCAE 2.1 for DOS and the screen still jitters, but
>this seems to be a bug within PCAE.
>The problem is here:
>F505    8502    STA WSYNC
>Because of previous branches, on even frames you reach it at scanline 68,
>colorclock 6, and on odd frames at scanline 67, colorclock 225.
>On both cases, after WSYNC (I think) you should be at scanline 69,
>colorclock 0. But on odd frames PCAE leaves you at scanline 68, colorclock
>0, and that makes the rest of the frame to be displayed one scanline

Did you disassemble and go through it? Yikes! (but thanks!) if the source code would be helpfull just let me know. I do plan to post it eventually but at the moment it's basically uncommented (except where I wanted to remind myself what the hell I'm doing...). However, if you're going to be going through it anyway, the label names and formatting may make things a little easier to read.

Unfortunately I've been tinkering a little so things have move a bit - enough anyway that I can't identify which WSYNC (There are a few...(smile)). Can you tell me the lines directly preceeding or following that STA WYSYNC you've mentioned above? Maybe I can add a NOP or two to the odd frames....

If that's even needed still - Attached is the most recent which seems to be jitter free on any emulator I've tried (Pcaewin, StellaX and z26) as well as the real hardware (though my tv is more resistant to roll than most). I'm a lot more concerned about the real hardware but still if it's a small matter to have it running properly on all emus too I'd just as soon have it doing so...

[Just grabbed PCAE-DOS but can't seem to get it to run on my system (WIN-ME)]

>Maybe the 7800 behaves different from the 2600 when you do a WSYNC so close
>to the end of the scanline.

Maybe PCAE DOS more closely resembles the 7800? (Strange that Pcaewin doesn't show this behaviour though...)

(You'd think this wouldn't be the first time someone's done WSYNC close to the end of a scanline (Then again, it's only noticeable because it's different every other frame. If it was doing it every frame it would probably go unnoticed...))



Archives (includes files) at
Unsub & more at

Current Thread