Titan Overdrive demo crashing

Hey all

Before anyone says so, yes I know this demo is designed to work in 50Hz mode only and will freeze in 60Hz mode. My issue is, even when I set my MD to 50Hz mode, it crashes right near the end, displaying inverted colours and a continual note from the YM2612. It's not a hard crash as hitting reset still gets back to the menu on my EverDrive. One thing to note is my MD has a proper NTSC master oscillator installed, so when running in 50Hz mode, it is ever so slightly faster in terms of refresh rate than a bone stock PAL MD. I wonder if that might be the cause? I know that the demo producing those visuals is heavily tied to CPU timing, so perhaps that small discrepancy is enough to get it to crash. Any thoughts?

Different oscillator won't make a difference, cycles per line, frame and other important times remain constant.
I would imagine that the Everdrive is to blame hehe.

Interesting. Because the everdrive is brand new, and its diagnostics come back green across the board.

I had the same issue through my MegaED X7 as well. I just view it using the later done NTSC compatible version of the demo.

That’s the version I am using. Still crashes.

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Originally Posted by Xaranar

That’s the version I am using. Still crashes.

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Okay, well the NTSC compatible version doesn't run at 50hz. It has been sync'd to run at 60. So you don't need to drop the speed down. If you are, then that is likely the issue.

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Originally Posted by CrossBow

Okay, well the NTSC compatible version doesn't run at 50hz. It has been sync'd to run at 60. So you don't need to drop the speed down. If you are, then that is likely the issue.

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Sadly, that doesn't work either. It actually crashes much earlier on when running in 60Hz mode.

So after further investigation, it always crashes in the same place - the 512 colour screen. I’ve swapped both the VRAM and SRAM, same issue, so I think it might be the VDP. I tried it on my model 2 and that works flawlessly, so that narrows it down to the VDP or maybe the CPU?

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Originally Posted by CrossBow

Okay, well the NTSC compatible version doesn't run at 50hz. It has been sync'd to run at 60. So you don't need to drop the speed down. If you are, then that is likely the issue.

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This is wrong, the demo is still designed for PAL. In fact, some effects just pause on every third frame to match the speed on 60hz.

I'd also like to blame the Everdrive, but you can never be sure. Does this happen with the original release too? (https://files.scene.org/view/parties...vemegademo.zip)

Regards,
Oerg866

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Originally Posted by Oerg866

This is wrong, the demo is still designed for PAL. In fact, some effects just pause on every third frame to match the speed on 60hz.

I'd also like to blame the Everdrive, but you can never be sure. Does this happen with the original release too? (https://files.scene.org/view/parties...vemegademo.zip)

Regards,
Oerg866

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I assumed it the NTSC compatible version was synced at 60hz because the graphics and sound match up unlike when I run the original release where the audio and video aren't quite matched. Eitherway, the version I have of it does run to the end without lock ups on my MegaED X7

Yeah, it's not the Everdrive, as it runs flawlessly on my Model 2. I think there is something up with my VA6. I tried swapping out a bunch of parts, and now the system doesn't even boot properly xD. Oh well, I guess I'll just have to grab a new one! Good thing they aren't expensive.

This is not the first time I heard about such crashes but I don't have an affected Mega Drive for investigation. Does this always happen at the same moment during that scene? Can you record a video from at least the start of this scene to the crash happening? (doesn't have to be high quality, pointing a mobile phone at your TV screen will already do the trick)

An update on this. So I got another MD, exactly the same board revision, and it exhibits the same problem. Running fine up until the 512 colour screen, then crashes as soon as that displays. Maybe it’s something to do with the VA6? Interestingly enough, they have the Hitachi CPU, so I don’t know if that has anything to do with it. I’m going to do some more testing after swapping the Hitachi for a true blue Motorola MC68000P8.

And a further update, I got hold of a VA4 revision, and that works perfectly fine, runs all the way to the end, no problems at all. There must be something about how the VA6 is put together that causes the incompatibility.