GTA02 USB and battery current profile

[Felipe Balbi]

On Sun, Mar 09, 2008 at 08:24:33AM -0300, Werner Almesberger wrote:
> Felipe Balbi wrote:
> > Ehehe, pm chips... you never know:-p
> 
> Yeah, it's a complex beast for sure. But in general, it's behaving,
> so I hope this is something we can solve.
> 
> > How are you triggering usb charging, btw?
> 
> We charge with 500mA if the host signals that we can, and we detect
> our charger through a 48k, 1% resistor between ID and GND.
> 
> Our charger doesn't short D+ and D-. That new standard came too
> late for that :-(

But you're misusing id pin. This is a huge hardware issue and should be
solve asap. Id pin should generate an interrupt to the otg transceiver
for it to switch between host and peripheral roles.

Also the drivers/usb/gadget/ether.c modifications is wrong. It will
never work on otg sessions at all.

Instead of hardcoding 500mA current draw in the config descriptors, you
should add 2 sets of them:
1. drawing 500mA
2. drawing 100mA

If we're in an otg session, the first descriptor will be rejected and
the second one will be chosen for work ;-)

BTW, really precise resistor you got:-p
1% tolerance, wow. That must be kinda difficult to find :-p

-- 
Best Regards,

Felipe Balbi
me at felipebalbi.com
http://blog.felipebalbi.com