Okay, let's see if I'm the only one with this problem.
macOS 11.2.3 (Big Sur)
VICE GTK 3-3.5
VIC-20 (pretty much the only one I use)
Quite frequently, the emulator starts going super-fast, with CPU% going over 4000% or so (about 2/3 of "warp speed"). I can bring it back to normal by activating then de-activating Warp with Cmd-W x 2.
I have tried setting Maximum Speed to 100% and Maximum FPS to 60.
This is almost guaranteed to occur if I go do other things, and then come back to VICE. But it also happens very often (3-4 times per hour of use) while I'm just using VICE normally. I'll press DEL and suddenly half the screen will be gone. I've become conditioned to quick Cmd-W, Cmd-W, but it's still kind of annoying.
VIC-20 Projects: wAx Assembler, TRBo: Turtle RescueBot, Helix Colony, Sub Med, Trolley Problem, Dungeon of Dance, ZEPTOPOLIS, MIDI KERNAL, The Archivist, Ed for Prophet-5
