Has anyone thought of developing an exerciser for the Intel MCS-51 instruction set and standard onboard peripherals (timers, interrupt controller and serial channel), like ZEXALL for Z80? It would be very helpful for testing MAME and other emulators, and not an outrageously esoteric project considering how old and widespread the MCS-51 architecture is and how grounding the EA pin allows most models to be tested without reprogramming the internal ROM (if they have any).

The 80(C)31 and 80(C)32 have a few undocumented behaviors that might well differ between models and manufacturers, such as the values of ACC and B after dividing by zero, what the "reserved" opcode 0A5H actually does (aside from its documented use in the MCS-251's extended instruction set), and whether or not PSW.1 exists. Those would be worth researching in themselves.