EHCI handoff



I don’t get it. I mean the sense of the “BIOS EHCI Hand-Off” entry in some BIOSes. XP/Vista take over control over EHCI. Period. That’s what sounds logical and what everyone would think, isn’t it, wouldn’t you.

But why did Microsoft then release a statement (longer time ago), that xp SP2 introduces a preliminary(!) EHCI hand-off from BIOS?? Why wasn’t it there long before xp SP2 and xp in general? Is the EHCI hand-off final in Vista or still “preliminary”??

Is the “EHCI Handoff” BIOS entry a workaround then, and pre-sp2 xp only works with USB2.0 devices because that workaround has been implemented and hidden in several BIOS generations??

As said, I don’t get this at all… :confused::confused:


[quote=georgekellerman;2009523]and pre-sp2 xp only works with USB2.0 devices because that workaround has been implemented and hidden in several BIOS generations??[/quote]XP Pre-sp2 is SP1 ;). USB 2.0 support came with that first service pack. Other users without SP installed could use drivers proviced from the mainboard or controller card manufacturers.



Thanks for answering! :slight_smile:

But what exactly is the “BIOS EHCI Hand-Off” [Disabled] [Enabled] entry? Should this be enabled with 9x/NT/xp and disabled with xp SP1/xp SP2/ Vista? Or should it be disabled with 9x/NT/xp and enabled with xp SP1/xp SP2/ Vista? Is this BIOS function a workaround? And for what actually??

This is from an ASUS manual (BIOS section):

BIOS EHCI Hand-Off [Disabled] [Enabled]:
Allows you to enable support for OS without EHCI hand-off feature.

I understand that xp SP1 and later have USB 2.0 support. What OS - xp/xp SP1/xp SP2/ Vista - has no “EHCI hand-off feature” as written in the quote above? What OS (xp/xp SP1/xp SP2/ Vista ) has “EHCI hand-off feature”?

And this is from a Microsoft FAQ:

What features of the USB EHCI specification are not yet implemented?
Windows XP supports a number of features in the Enhanced Host Controller Interface (EHCI) specification, but there are a few features that are not implemented. These features may be supported in future releases:

• Features added to EHCI in or after version 0.95.
• Rebalance Lockout (I-Bit)
• Frame Span Traversal Nodes (FSTN)
• 64-bit host controller addressing support. EHCI controller can still work in 32-bit mode on an x64 or Intel Itanium platform.
• Kernel Debugging over USB 2.0.
• EHCI BIOS handoff.
• BIOS vendors should support the EHCI BIOS handoff section in the EHCI Specification for all EHCI-aware BIOS
• Preliminary support for EHCI BIOS handoff will be available in Windows XP SP2. The Windows core team for USB would like to work with OEM partners and BIOS vendors to develop this functionality.



As you can see in this quote, USB 2.0 support may have, as you have said, started with xp SP1, but the functionality called “EHCI BIOS handoff” started with xp SP2, and even in xp SP2 it was not final but preliminary.

What does all this mean? :confused:


Maybe this is useful for you? (page 121)