USB power direction in host mode (was: Re: 3G USB Dongle (was Re: Neo as cellular modem?))

[Joerg Reisenweber]

Am Do  29. Mai 2008 schrieb Michael Shiloh:
> 
> Andy Green wrote:
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> > 
> > Somebody in the thread at some point said:
> > | Am Mi  28. Mai 2008 schrieb Brad Midgley:
> > |> Joerg
> > |>
> > |> On Wed, May 28, 2008 at 2:30 AM, Joerg Reisenweber <joerg at openmoko.org>
> > | wrote:
> > |>> Am Mi  28. Mai 2008 schrieb Brad Midgley:
> > |>>> i think it may still be up in the air
> > |>> Nope it's not, see Y-cable in wiki. Should work perfectly. You just
> > have
> > | to
> > |>> find the 5pin-mini-USB-plug to DIY one.
> > |> is EN_USBHOST is deasserted by the system automatically now? I'll
> > |> update the section in
> > |> http://wiki.openmoko.org/wiki/Neo_FreeRunner_GTA02_Hardware if it is.
> > |
> > | No idea, it's a driver issue. On detection of 47k device is switching to
> > | fastcharge, which I think is actually working. Also it should activate
> > | LOGICAL hostmode for USB-controller same time (NOT asserting
> > EN_USBHOST!),
> > | which is needed for Y-Cable and doesn't hurt charger. I don't have the
> > | slightest idea whether this already is in kernel or not.
> > 
> > It is deasserted if it sees you have a 1A charger in there, has been for
> > a while.
> 
> A related question: I presume that it is the electrical signal 
> EN_USBHOST which flips the switch which causes the USB port to source 
> current in host mode, as opposed to sinking current in device mode.
> 
> This is of course what is expected of a USB host, but it also prevents 
> us from charging the Freerunner when the USB port is in host mode, if an 
> appropriate power source is available.
> 
> Question:
> Is it possible to charge the Neo Freerunner when using the USB port in 
> host mode, by ascerting LOGICAL hostmode and by NOT asserting EN_USBHOST?
 
that's exactly how Y-cable_V1 *) works (besides replacing the needed 15k? 
pulldown-Rs also switched away by deasserting EN_USBHOST)
The combination LOGICAL hostmode + NO chargepump is exactly what the 
kernel-driver should initiate when seeing 47k


*) There's the spec for V2 already, that's capable of working with USB2.0-OTG 
(supported by GTA03, though USB2.0 will be there with GTA04 at the earliest)
See "Y-Cable revisited" somewhere on the lists - even more simple ;-)

/j
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