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My dev machine has no real 8042 controller/ps2 ports etc. There exists a bios option to use legacy mode with the usb host controller, I had a few questions related to that.

First, it says it uses SMI to copy the relevant mouse/kdb data from usb mmio locations to ISA legacy ports. Does this mean that the related interrupt for the usb host controller (on pci, inta, intb etc) must be configured for SMI within the IOAPIC? or am I thinking about this all wrong.

Secondly, if it is.. what happens if another device is sharing that same global system interrupt but it's configured for SMI.

Third, I would assume that with a usb host controller in legacy mode, that you cannot use it for any other purpose?

Thanks

It basically means "designed to also mostly work with DOS and make no difference for recent Windows" rather than "designed for recent Windows". The moment you do things DOS never does, like resetting the KBC, accessing the APIC components or the USB components, whatever scheme the BIOS might have set up gets screwed over.

You'll probably find yourself without input devices until you deal with all devices properly and thoroughly like a "quality" OS - at which point all remains of the emulation are gone as well.

How the BIOS and chipset actually agree on the emulation is their own thing, differs between motherboards, and probably doesn't concern you anyway since the proper solution ignores the whole situation altogether.