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Alien Hack...causing scrolling screen with Harmony Cart


StephenJ
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Another little problem with the hack is on the second screen, you have to push down before you can move up. Otherwise you're stuck at the bottom.

 

I noticed this. At least it is a known issue and relatively easy to deal with.

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I tried the game tonight, on my Jr. I have the same screen issue. It's not really scrolling, but it does jump horribly. It makes it completely unplayable. So, I tested it on my Vader and my 7800. It still had the jumping issue. It's unplayable. I don't see why someone hasn't already fixed it. I would, but I'd have no clue where to even begin. :?

Edited by RamrodHare
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Sure, whoever hacked it needs to fix their VSYNC routine. It's only holding it for 1 scanline, a TV needs the VSYNC signal to be held for 3 scanlines.

 

If you're asking me to fix it, sorry but no. Without source it's not something I could quickly fix, and my plate is full as I need to finish this in time for this.

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This was done by Kurt Howe, back in 2005, I think. I tried to look him up here on the forums and on google, but I didn't have any luck finding a way to get in touch with him.. :(

 

I found this info , so I'm going to see if I can figure out how to fix the issue. It seems simple enough, but I got stuck trying to hack colors not long ago. This is all new to me, but I have to learn sometime! :)

 

3.3 Vertical timing

When the electron beam has scanned 262 lines, the TV set
must be signaled to blank the beam and position it at the
top of the screen to start a new frame. This signal is
called vertical sync, and the TIA must transmit this signal
for at least 3 scan lines. This is accomplished by writing
a “1” in D1 of VSYNC to turn it on, count at least 2 scan
lines, then write a “0” to D1 of VSYNC to turn it off.
To physically turn the beam off during its repositioning
time, the TV set needs 37 scan lines of vertical blanks
signal from the TIA. This is accomplished by writing a “1”
in D1 of VBLANK to turn it on, count 37 lines, then write a
“0” to D1 of VBLANK to turn it off. The microprocessor is
of course free to execute other software during the
vertical timing commands, VSYNC and VBLANK.
Edited by RamrodHare
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I just realized that it says 2010 on the title, so this isn't as old as I thought, but it doesn't change the fact that I can't find a way to contact Kurt Howe. I have made a bit of progress using Stella to go through the code, but the version of Stella I have is having issues with crashing on Windows 7. I've got to get that sorted out before I can work on fixing this. I've found VSYNC and managed to make it roll on Stella, so I have a feeling I can just mess around with it until I get it working right, but I'll read through some more tutorials to see if I can get a better grasp on what I'm actually doing, instead of just changing values. :-D

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Not sharing anything that isn't already public knowledge... Kurt is "Nukey Shay".

 

Which also explains the very tight assembly code around the vsync that I saw when I looked into this hack earlier today. :)

That's news to me. :) I had no idea Nukey Shay was Kurt. I guess I wasn't looking in the right place. ;) Thanks for the info. :thumbsup:

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Sure, whoever hacked it needs to fix their VSYNC routine. It's only holding it for 1 scanline, a TV needs the VSYNC signal to be held for 3 scanlines.

 

If you're asking me to fix it, sorry but no. Without source it's not something I could quickly fix, and my plate is full as I need to finish this in time for this.

Thanks anyway...Have a great time at the Expo!

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