Problem with battery charging

[Ian Stirling]

Harald Welte wrote:
> On Wed, Mar 21, 2007 at 02:08:04PM +0100, Nils Faerber wrote:
>> Hi!
>> I just recognised a little issue with battery charging...

<snip>

> With devices up to GTA01Bv3 and the current charger we basically have no
> way of using a non-usb-host for charging without violating the USB spec.
> 
> So now we have the choice between USB incompliant 500mA charging (which
> might in some really bad cases cause damage to the 'usb host' it is
> attached to.

I'm pretty sure that the USB spec actually says it's mandatory that 
stuff shuts down without damage on overload.
This is my experience too.
> 
> Thus, we'd rather done it the safe way:  Only use 500mA after the USB
> host has granted us permission to do so.
> 
> I know that it's almost industry practise to violate this part of the
> spec.  However, OpenMoko wants to set a good example and adhere to
> standards :)
> 
> GTA01Bv4 and the new charger hardware contain circuit changes to address
> this problem in a usb spec compliant way.

This is a wrong way to solve this IMO.

If the charger is simply a dumb charger, with a host chip or something 
in it to say "I'm a neo charger", then why on earth should I prefer it 
over my existing USB charger that has UK/EU/US/japan plugs integrated 
into one comparatively small package.

Also - IIRC - it's been a while, but windows won't actually enable a 
device to take 500mA without a driver, so you can't plug it into a 
random PC to charge.

I'd suggest a compromise.
A host that does not communicate over the USB bus is not a compliant 
host AIUI.

If there is power to the port, and the host has not requested our 
configuration in the first few seconds, then optionally either switch to 
'fast charge' mode (unless on last switch to fast charge mode the 
voltage went away) or pop up a box to the user saying 'do you really 
want to do this?'

The ideal solution would be this, and some reason for me to prefer the 
USB charger.

My ideal neo charger would start with 
http://www.ebuyer.com/UK/product/106335 - this has replacable tops.
Replace the existing simple 5V charger top, with a slightly more complex 
one.

This would have two or more 'A' sockets.
You take an A->mini-B cable, and plug it into the neo on one end and the 
charger on the other.
Then the other port lets you connect a printer, keyboard, hub, or other 
USB device to the neo.

For other devices this would simply act as a dual USB charger.