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

Federico Lorenzi florenzi at gmail.com
Thu May 29 07:30:50 CEST 2008


On Thu, May 29, 2008 at 4:18 AM, Joerg Reisenweber <joerg at openmoko.org> wrote:
> Am Do  29. Mai 2008 schrieb Michael Shiloh:
>>
>> Andy Green wrote:
>> > -----BEGIN PGP SIGNED MESSAGE-----
>> > Hash: SHA1
>> >
>> > 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 ;-)
I sense a leak of details :) What is the GTA03 that you speak of... I
know GTA04 is the next revision being discussed on the mailing lists,
but I thought GTA03 was skipped?

Cheers,
Federico




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