> -----Original Message-----
> From: Alan Stern [mailto:[EMAIL PROTECTED]
> Sent: 2007 July 30 15:21
> To: Dave Higton
> Cc: [email protected]
> Subject: Re: [Linux-usb-users] device descriptor read/8, error -110
>
> 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.
Yes, I'd spotted and cited that one.
> 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.
But where is it documented that USB 2.0 is backward compatible with
USB 1.1? Does one have to read and compare every paragraph of the
two specifications?
USB 2.0 contains a statement that 2.0-compliant hosts must operate
correctly with 1.1-compliant devices, but that's a much weaker
statement than "USB 2.0 compliance requires USB 1.1 compliance"
(which is what I claimed, but was unable to back up) or "every
USB 2.0 device is required to be compatible with a USB 1.1 host".
Dave
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