- Writes to $8000 with a value greater than 7, no matter from which register the write came
- Writes to $8001 with bit 4 = 1 while $8000 is 0 or 1
- Writes to $8001 with bit 4 = 0 while $8000 is 2, 3, 4, or 5
Or would it be better to modify an emulator's source code to support the subset directly?