I’ve been looking into the wonders of USB3 and am confused. The new generation of Dell computers we've been testing come with Renesas USB Host Controllers (which Intel supply on-board). This host controller is compliant with both the USB3 and xHCI (extensible host controller interface) specifications. Drivers exist for Windows platforms XP and above for this controller.
Below is the Internal block diagram for Renesas µPD720200 USB3 Host Controller
The problem however seems to be that Intel only supports the USB 3.0 xHCI driver on Windows 7. For Windows XP and Windows Vista, a BIOS tweak is required to downgrade these ports to USB2 (thereby allowing the EHCI driver to kick in). So.. for those manufacturers which haven’t provided this BIOS tweak you are left with dead USB ports once booted into Windows XP and Windows Vista.
Here's the intel link for the no support option for xHCI for anything other than Windows7
My questions, if they can be answered are;
1) Why drop USB3 support for XP/Vista when in the Enterprise still 40% of systems are on XP and the microcontroller itself has XP support. It also seems odd as to even get them functioning as USB2 the vendor needs to put in place a BIOS fix? I would have thought it was less effort just to deliver the driver than develop a workaround for vendors to implement.
2) How does the driver interplay work here? Renesas supply XP drivers for the controller, but Intel don’t supply xHCI XP drivers. The Renesas block diagram seems to suggest that is encompasses the extensible host controller. It would seem through that it doesn’t, and it’s actually more of USB Root Hub that ‘talks’ to the systems xHCI controller? Is this why two drivers are required?
Sorry if this is hazy –I did say I was confused…… Is this something anyone can shed light on?