superfury wrote:

Should I include it as an option to be enabled (disabled by default) in my emulator? So the user of my emulator can enable the VGA NMI on precursor register access, which don't exist in my VGA? This will be in the advanced menu of course, since normal users won't know when to use it, together with the other misc. options? Currently ports 3B8, 3D8 and 3D9 generate a NMI when enabled. Is this correct?

I'd say no - don't include it, unless you're actually emulating a specific SVGA card which does do this. Then do it but only once you're emulated enough of the SVGA's BIOS and other hardware that it does the right thing.

Better just stick to analyzing what is actually needed to get the emulator running with your target bios/game whatever. Getting sidetracked on emulating something that nothing needs or uses so you can't even test it is just a big waste of time 😀