Re: device descriptor read/8, error -110

[Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>]

On Mon, 30 Jul 2007, Dave Higton wrote:

> > 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?

You probably do.  The specification doesn't state explicitly that it is 
backward compatible with USB 1.1.

> 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".

As far as I know, the differences between the way a USB 2.0 device and
a USB 1.1 device are required to behave when connected to a USB 1.1
host reflect either errata in the 1.1 spec or new restrictions.  But
the 2.0 spec doesn't say this; in fact it hardly refers to the contents
of the 1.1 spec at all.

Alan Stern


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