From: Li Yang-r58472 <[EMAIL PROTECTED]>
To: Steve Calfee <[EMAIL PROTECTED]>, [EMAIL PROTECTED]
CC: linux-usb-devel@lists.sourceforge.net
Subject: RE: [linux-usb-devel] Re: Question about OTG operations
Date: Wed, 1 Mar 2006 14:44:31 +0800
> -----Original Message-----
> From: [EMAIL PROTECTED]
> [mailto:[EMAIL PROTECTED] On Behalf Of Steve
> Calfee
> Sent: Wednesday, March 01, 2006 2:21 PM
> To: [EMAIL PROTECTED]
> Cc: linux-usb-devel@lists.sourceforge.net
> Subject: RE: [linux-usb-devel] Re: Question about OTG operations
>
> >On Tuesday 28 February 2006 7:44 pm, Li Yang-r58472 wrote:
> > > Thanks Dave,
> > >
> > > So the current application of HNP is only to correct wrongly
connected
> >cable?
> >
> >That's not what I said, but it _is_ the only scenario that's completely
> >spelled out in the specs.
> >
>
> One other really useful aspect of OTG is power. If you have a battery
> powered device connecting to another powered device it is useful to have
the
> A end pointed at the powered device.
>
> So for instance if you have a battery powered PC and wish to connect it
to a
> powered printer or a display device it would be nice if the A connector
goes
> into the "peripheral" and the b into the "computer" that way the
computer
> would get power and the device could hand off the awesome responsibility
of
> knowing what to do to the computer.
That will need the user to plug the cable _correctly_. HNP won't change
the responsibility of power supply to the bus. Is it a drawback of current
OTG spec?
Yes, it is a huge drawback to the spec. Being host does not say you provide
power, being "A" connector does. How do you communicate the fact that your
handheld can use and get power from a device if it is plugged in properly.
I have seen more devices with both A and B connectors, but that do not have
an OTG connector. However, the A device is only guaranteed to supply 8ma, so
only a "system" involving both a battery powered "pc" and a powered device
could even handle the obvious power handling used in OTG. Probably having
both A and B connectors is a more sane and clear indication of power and
connections.
Regards, Steve
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