Yeah, I’ve been working on improving the bus emulation, particularly the address map stuff using the new hook system. In my branch, I have an MVME050 SYSCON card that installs itself over the entire VME address space. It acts as a memory bus device of last resort, asserting /VBERR on access after the bus timeout period if no other slot device is overlaying an address. All slot devices pick that up and fire the appropriate callback. This is good enough to get the 120bug firmware to think there’s an 050 available (though I don’t have bus interrupts hooked up yet…)