Re: USB OTG HNP (can you find any other appropriate TLAs?)

On Friday 25 May 2007, Alan Stern wrote:
> On Thu, 24 May 2007, David Brownell wrote:
> > On Thursday 24 May 2007, Alan Stern wrote:
> 
> > > After all, an OTG device is required to have no  
> > > more than one USB connection, so the port number would always be equal 
> > > to udev->portnum and to 1.
> > 
> > Not true.  It's perfectly legit for a host to have multiple host
> > ports, with only one of them being OTG-capable.
> 
> Really?  What about section 3.2 in the OTG spec, where it says that an 
> On-The-Go device must include:
> 
> 	one, and only one connection: a Micro-AB receptacle.

You omitted the "(except as noted in Section 3.8)", which says
that a second connector is allowed iff it's a Mini-A connector.
That's a trivial counter-example...

But in any case, section 3 is only talking about connectors,
not links that may be used internally on a mainboard and which
would not be externally visible.  The example I gave was for
an on-mainboard device.  (I've seen similar products using
SDIO to access modem chips.  Again, nothing visible to the end
users; just boards leveraging volume pricing for parts using
a wire-efficient I/O bus.)


> Has this been superseded?  Or do people simply ignore it?

Rev 1.2 changed from 1.0a here; ISTR that 1.0a allowed more
than one such connector, and allowed standard-A too.

But also keep in mind that the constraint is on externally
visible connectors, to reduce end-user confusion.  And that
as the section 3 intro says, the text there doesn't address
technical details ... just the highlights.

- Dave


> > 		 Not uncommon either;
> > it's a simple implementation strategy (combining existing silicon IP
> > with an OTG engine), and board designers find serial busses like USB
> > are handy as a way to integrate various devices ... simple to route
> > on the boards, only two pins, and so forth.  It's not just a way to
> > connect external devices.
> 
> Alan Stern
> 



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