Extra Terrestrials (no, not that one) - Emulation Glitches

[+llabnip]

Okay hive-mind!  You guys are my best hope.

 

I've got an issue with my StellaDS emulator and the rare Extra Terrestrials (1984 by Skill Screen Games).

 

It's a simple 4K game but it's doing something that I'm not handling correctly. Mainline Stella, as you would expect, plays it perfectly.

 

When the game is rendered on StellaDS, there is something "off" about the two player sprites (at least I'm assuming they are P0 and P1...). The ET looking sprite is offset too far to the right. It should be closer to the green C.  Same with the man-looking sprite at the bottom - it should be more left (though it is slightly offset just as you see from the ET looking sprite).

 

Further, when the ET looking sprite is at position A, it will be "eating dots/road segments" at position B.  So the game plays the same as it does on Stella or real hardware except both player sprites appear to be offset in the X direction.

 

Since my emulator is based on older Stella (with the position hacks to handle reset of player/missile/ball "too soon") I though it might be similar but I put a trap on hitting those TIA registers "too soon" and didn't see it. 

 

So I'm at a loss as to even where to start looking for this problem in my code...  any hints, guesses or conjectures could go a long way to helping me find it. Admittedly, this one game isn't worth a ton of effort but I'd still like to get it playable!

 

[Thomas Jentzsch]

Maybe the game overwrites HMPx too early?

[alex_79]

The issues with "Extra Terrestrial" are related to RSYNC emulation. It was fixed in Stella 3.8.1.

 

https://github.com/stella-emu/stella/commits/release-3.8.1

[+llabnip]

You guys are awesome. Didn't even finish my 2nd cup of coffee and now I've got the clue I need!

 

And just like that... perfect. I'm a little embarrassed - I should have been able to google my way through this one. But I do appreciate the assist!