Rom freezes after 2 minutes on my Phoenix

[JOD-I]

Using my Phoenix, It seems that Star Fortress freezes up after about 2 minutes of gameplay regardless of whether I play the game from my SD card or the Atarimax Cartridge. It seems to be just this game. Any ideas on what is going on?

[JOD-I]

I dont know if this makes a difference but the game is star force not star fortress. sorry for the error.

[Ikrananka]

I see the same problem.  I'm investigating where it does and doesn't work and will report back tomorrow.

[Ikrananka]

After some testing, and what a great game by the way, I believe I have it narrowed down to the F18A as being the most likely source of the problem.  I tested my original cart, the rom in an AtariMax Ultimate and the rom via the Phoenix SD slot in a stock unmodified CV, an F18A modded CV and the Phoenix.  I found that the rom and even the original cart misbehave and freeze after a variable amount of time in my F18A modded system and the Phoenix.  However, the original cart and the rom in my AtariMax work flawlessly in my unmodified CV.  So, the F18A is a common factor.  I wonder if the F18A functionality can be completely disabled in the Phoenix.  I'll check with CollectorVision.

[Tursi]

The answer is no. The F18A is not an add-on, it's a replacement VDP. If you disable the F18A, there's no video.

 

[Ikrananka]

So after some discussion, it appears that the problem appears to be the way the game was coded making it very sensitive to any timing differences between hardware that the game is being run on.  CollectorVision experienced the problem on a stock ADAM system but conversely had it work fine on one of their F18A modded CVs (while it freezes on mine).  So, in effect it's a bug in the game code that may or may not occur depending on the hardware the game is being run on.  Unfortunately, the Phoenix is one of those systems that appears to consistently run into the bug.  Interestingly, and fortuitously, the game rom appears to work without freezing with CoolCV v0.6.9 and ColEm v5.5.

 

This problem was also identified way back in 2013

 

 

[Ikrananka]

Good news, I'm delighted to say that Tursi managed to identify a small fragment of badly written code (a loop) that is causing the game to freeze on certain systems, including the Phoenix.  While it always freezes on the Phoenix, the likelihood of the freeze occurring on other hardware and on most emulators appears to be much less but nevertheless may still occur at anytime during a game even if it doesn't freeze during the first few minutes.

 

Note that the offending piece of code appears to be part of the original SG-1000 code from which the CV version of the game was converted.

 

Tursi has created a patch which simply bypasses the loop thereby preventing it from getting stuck.  It is a simple 2 byte change.

 

Publishing rights for the CV version of the game have been passed back from Team Pixelboy to Opcode Games and Eduardo has very kindly allowed me to post the patched rom here on AA (attached to this post).  However, be aware that this patch is not a fix but more of a hack to bypass the issue and as such it may well cause other issues that are currently unknown.  However, in my testing of the game through to Level 7 on multiple systems I have experienced absolutely no issues at all and it now runs without freezing on the Phoenix.  Let me know how you get on.

StarForcePatchedTursi2.zip

[Ikrananka]

Well this is disappointing to report but the patched rom is now regularly freezing in my F18A modded CV.  Good news is that it still works without freezing in my Phoenix after playing quite a few more games.

[JOD-I]

Thanks to everyone involved in fixing the rom