Re: device descriptor read/8, error -110

[Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>]

On Mon, 30 Jul 2007, Dave Higton wrote:

> > According to the spec, every USB 2.0 device is
> > required to be compatible with a USB 1.1 host.  It isn't required to
> > provide full functionality --
> 
> Do you have a "chapter and verse" reference for this?  I stated
> it to someone on a newsgroup recently; he then challenged me to
> provide a reference.  I skimmed and searched the USB 2.0 spec
> but failed.

Here's one sentence in section 7.1:

	An upstream facing high-speed capable transceiver must not
	operate in low-speed signaling mode, but must be able to
	operate in full-speed signaling mode.

More to the point is this sentence in 9.2.6.6:

	A device capable of operation at high-speed can operate in
	either full- or high-speed.

That's not exactly the same as being compatible with a USB 1.1 host; 
the rest of it follows from the fact that the 2.0 spec is backward 
compatible with the 1.1 spec.

Alan Stern


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