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Report from @Tatsuya79:
Trying to use run ahead with this core, it’s misbehaving in various ways.
For Bubble Bobble (Japan, Ver 0.1), Thunder Force AC and others I forgot:
-1 instance mode: seems to reduce the input lag by the desired amount of frames but sound issues -2 instances mode: strange behaviour, needs to specify a higher number of frames to reduce than what should be needed, hiccups on button push (looks like some frames are skipped when using next frame step with K hotkey)
Guwange: run ahead not working at all despite save state support, got a black screen once when activating 1 instance.
You can see this other thread for a “Debug Runahead” fork of Retroarch posted by Dwedit (September 25th near the end) if you’re interested into solving that issue.