freerunner: charging and usb-host mutually exclusive?

Andy Green andy at
Tue Mar 11 21:58:37 CET 2008

Hash: SHA1

Somebody in the thread at some point said:
> Hi Andy!
> Am Di  11. März 2008 schrieb Andy Green:
>> - gpg control packet
>> Somebody in the thread at some point said:
>>> Andy
>>>>  Currently the pump that provides 5V for the external device is enabled
>>>>  whenever we are in host mode.  I don't know what that thing will do if
>>>>  we provide 5V externally too, probably it will be okay but it needs 
> testing.
>>> You wrote "currently". Does that mean with a software change we might
>>> turn off the pump and reenable charging while in host mode?
>> The situation is that there is only one bit that controls if we are
>> physically in host mode (this bit comes out of a PMU GPIO and can be
>> controlled by the CPU).
> This bit not only controls the power pump and pulldown, but also the U4905 
> RT9711BPB power switch for _inbound_ power supply. So for the given 
> hw-design, there's no way to have 
> the GTA02 powered from outside (this is the point!) 
> while in hw-hostmode.

WAH missed U4905, you are quite right Joerg :-(

>>  it won't "see" the insertion.  I guess you could add 15K pulldowns
>> permanently if you knew you would only use it in externally-powered-host
>> mode but it is a bit sucky.
> Well, i understand you suggest to detect insertion of usb-device and high 
> speed mode while pulldown on, and then (triggered by some user interaction -  
> for we just can't detect the power reverse feed, that is if pump won't smoke) 
> switch EN_USBHOST GPIO to disable pump (and pulldown) and enable 
> charging/powering the GTA02 via RT9711BPB & PMU, while still keeping logical 
> hostmode for the interface.
> Right?

No, I was just noting you could put the CPU peripheral logic into host
mode but leave the EN_USBHOST signal low.  Then you could add 15K
pulldowns as a hack, and it would all work.  But it is a bit of a mess
and would then only work in this externally powered host mode.

> Anyway not having external power at all while in logical hostmode seems to be 
> a nogo. This has to be solved somehow. 

Too late I think :-/

> BTW: all this might be a lot easier with a simple coax type power connector 
> for feeding PMU *external_charger* path by a simple classic nokia style wall 

Wah dude it is great hearing from you :-)  You're catching my errors and
you read the datasheet :-)))  That's right the PMU "adapter" path is unused.

>> So we must do the test to find out where we are.
> I'm sure the pump won't care, but that's not the point.

Yeah the pump didn't care.  But your observation about U4905 explains
why HDQ reported no charging with EN_USBHOST asserted... it wasn't
because the battery suddenly became full :-((

- -Andy
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