[maemo-users] N900: Force charging on USB?

From: Kimmo Hämäläinen kimmo.hamalainen at nokia.com
Date: Wed Apr 14 14:11:47 EEST 2010
On Wed, 2010-04-14 at 12:58 +0200, ext Nils Faerber wrote:
> Joerg Reisenweber schrieb:
> > [Nils Faerber Di  13. April 2010]:
> >> I am preparing for a vacation and want to avoid carrying too many
> >> accessories.
> >> So I took my universal USB charger (which is just a USB plug carrying
> >> the +5V) plugged in the Nokia micro-USB cable and connected to the N900.
> >>
> >> Well, it does not charge - in contrast to almost any other device.
> > 
> > Probably it does, just it charges at 100mA only, and it doesn't signal it's 
> > charging.
> Well, pitily it does not - I just checked with a "USB charger" which has
> a dual color LED turning red on current flow. When I connect the N900
> via the normal USB cable there it does not change in any way. Just
> connecting the charging adapter change the LED from green to green plus
> a little red which mean current flow (just from the regulator).
> So I think we can safely assume that a blank USB cable will not in any
> way charge, even not at 100mA.

AFAIK, the kernel detects the type of the charger (because USB host
requires some enumeration stuff), so you could probably hack it (with
your own risk).


> >> This is I think also perfectly valid since there is no host at the other
> >> end to negotiate the charging current.
> > 
> > No, according to USB specs any source of VBUS 5Volt USB has to deliver 100mA. 
> > And the charger chip enables charging @ 100mA when detecting external 5V on 
> > USB - completely compliant with these specs.
> Yes, sure. What I meant is, if the charger is designed in a way to only
> properly work when sucking more than 100mA it would be valid to refuse
> charging. If it could handle a 100mA slow charge but it apparently does
> not do that I would see this as a bug.
> >> So assuming I know what I am doing is there a way to enforce the N900 to
> >> start charging even if there is no host connected? This must work
> >> somehow since the power adapter presumably does not contain a USB host ;)
> > 
> > Exactly. The charger shorts D+ and D- data lines of USB port.
> > This should enable fast charging
> Ah!
> I will try that - press thumbs that it works ;)
> >> Some fiddling with /sys/... or DBus would be fine with me...
> > 
> > Alas we got no sysfs nodes (yet ;-D ) to control the BQ24150 USB charger chip 
> > directly. BME does all the 'magic' for now, and afaik there's no API to tell 
> > BME to switch to a different charging mode.
> Umpf... too bad.
> The D+/D- trick sounds promising, many thanks!
> > cheers
> > jOERG
> Cheers
>   nils

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