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

Harald Welte laforge at openmoko.org
Sat Feb 3 14:54:19 CET 2007

On Wed, Jan 31, 2007 at 08:20:04AM -0700, Joe Pfeiffer wrote:
> Robert Michel writes:
> >> 
> >> Brilliant! Thanks for that :-)
> >
> >So now the question, how does an USB hub work?
> >Can we plug in the host on any port?
> Short form:  USB is strictly a hierarchical, tree-structured network.
> There is one host, which may connect to the upstream port on a hub;
> you can then plug in more hubs and devices downstream of the hub.
> They were very careful when writing to the standard to specify cables
> that can't plug in the wrong way:  you can only plug a host into the
> (single) upstream port on the hub.
> Long form:
> http://viper.cs.nmsu.edu:8000/classes/473/notes/usb.php?currentsem=s06
> Really long form (this is the USB 2.0 specification)
> http://www.usb.org/developers/docs/usb_20_05122006.zip
> >The Neo1973 will have mini-USB-B
> >
> >normal hubs powered USB-A for the adapter 
> >and one unpowerd USB-B for the host.
> My understanding is that it will be USB On-The-Go, 

No.  OTG is a complex specification, and it comprises way more than just
a AB socket, but also electrical and software components which we cannot
provide using the S3C2410.

All you need is a special Mini-B to regular-B cable, which you then can
plug in the upstream port of any regular self-powered USB hub.    You
can then use any (low-speed,full-speed) usb device on that hub. 

But that normal hub will not charge the phone, though.

FIC product development is looking in providing something that
conveniently solves this problem.  I cannot say more than that at this
point :)

- Harald Welte <laforge at openmoko.org>          	        http://openmoko.org/
Software for the world's first truly open Free Software mobile phone

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