MiSTer FPGA Forum

When playing GT1, about half the time or so the post-replay desyncs increasingly badly to the point your car never gets past the first lap and drives crazily.

It looks like the way replays work is that they just replay the control inputs and physics takes your car where it's supposed to be after, but I certainly don't recall the original game having a bug like this.

Anyone else seen it?

Apparently yes, never mind:

https://github.com/MiSTer-devel/PSX_MiSTer/issues/199

Yes, unfortunatly this is still in.

The issue with replays is that they must hit the exact same speed or higher when playing back. As the core aims for 100% original CPU speed, there is no buffer and some slight inaccuracies let it drop below 100% and result in a missed input for the replay, which can mess up everything.

There are 2 solution:

• 100% accuracy, which is very likely never going to happen with a system so complex
• aiming for higher than 100% CPU speed like you see in many emulators by default. In the core you can do that with turbo options.

Agree - I confirmed on this game in particular that medium Turbo is sufficient with no observable impact to gameplay as a whole, which is a reasonable compromise.

Thanks for weighing in!

@FPGAzumSpass - one thing I meant to ask about. In my experience, if you race without turbo but turn it on for the replay, the replay will still fail - if you turn on turbo before you race, the replay is fine. Wouldn't that imply that the real issue is with recording the inputs with sufficient fidelity vs. playing them back? Not sure that would have any impact on a cleaner workaround, just spitballing.

That's also possible, but i can't imagine how, as the gameplay of the US version often dips below 30fps on a real psx, so i'm not sure how it works then.