Q: How does USB hubs work? Re: Multiple USB Devices

michael at michaelshiloh.com michael at michaelshiloh.com
Wed Jan 31 18:44:55 CET 2007

On Wed, 31 Jan 2007, Joe Pfeiffer wrote:

> ...
> A compliant hub does not supply any power to the upstream device.  If
> you plug the Neo in to the upstream side of the hub (so it thinks it's
> a host), it can't be charged by the hub.  Of course, there are *lots*
> of noncompliant devices out there, including some that are expressly
> forbidden by the standard (but my USB "extension cord" is quite handy,
> thank you).  For that matter, the NEO's unpowered USB when acting as a
> host is already noncompliant.  No reason (other than compliance!) you
> couldn't build a hub that supplied upstream power, but I don't know of
> any on the market at the moment.
> ...

If anyone knows of a (non-compliant) powered hub that supplies upstream power,
please note it on the wiki. I have a feeling that this will be a much-demanded
accessory in a month or so.

Alternately, we just hack a USB charger (e.g. Lady Ada's minty boost mentioned
earlier) into a USB extension cable, and plug that into a compliant hub. If I
do this I will document it on the wiki.

It might be easy to hack a compliant powered hub to provide upstream power.
I'll keep my eyes open for one that is not glued together and try this.

Do we know if there is a risk to any other USB host (other than Neo) that is
plugged into such a modified hub? In other words, having made this hack, is it
best not to use the modified hub for anything other than the Neo?

A question for the FIC hardware people: devices that are charged via USB seem
to use the USB clock and data lines in different ways in order to inform the
device that they are connected to the charger. Lady Ada's website discusses
different combinations of pull-up and pull-down resistors needed to trick the
different iPod models to start charging.  Can this information be made
available for the Neo 1973?


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