[Nils Faerber Di 13. April 2010]: > Hi! > 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. > 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. > The normal way to proceed now would be to take the power adapter from > the N900 package, connect that to some +5V source and the other end to > the N900.Just that this power adapter has an integrated voltage > regulator which consumes quite some power on its own which I would like > to avoid (since I have a solar-cell battery pack which I would like to > use ;) Though you're basically right here, I'd not expect the efficiency of that adapter to be prohibitively low. I mean that's a small plastic case which gets considerably hot an a few tens of mW, and you want to charge with something like 5W max. Do the efficiency math yourself. > 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 > 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. cheers jOERG
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