Y-cable and USB-OTG: mutually exclusive / the four connectivity solutions

[Andy Green]

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Somebody in the thread at some point said:
| Andy Green wrote:
|> This is for the 500mA question?  Dunno yet, there can be pins on FTDI
|> that change state under this circumstance.
|
| There is :) Pin 41, PWREN# (nPWREN in Openmoko terminology).

Great.

But I have been reading the pcf50633 datasheet and we have to take a lot
of care about this.  Although there is a USB -> SYS programmable current
limit, there isn't one for adapter -> SYS.  We have only two handles to
use on this path

~ - dynamically claim adapter power is not present under MSP430 control
(we decide this externally anyway), so pcf50633 will not enable the
adapter -> SYS FET at all until we know we are good for <=500mA

~ - set charging current to zero

What we can't do is set current limit from adapter as we can on USB.  We
cannot actually treat it as a second USB interface for pcf50633 purposes
as it is I think.

|> I have a scheme for
|> detecting charger insertion though and that is what is critical.
|
| Ah, that sounds interesting. Have you figured out a way to detect
| shorted D+/D- ?

Yes I have a plan I will post about.  BTW I saw while looking at it that
it seems D- USB pin on GTA02 is floating when GTA02 charger is connected.

|> | to have a only 'dumb power' and 'jtag' port would be somehow
missing the
|> | point. especially when its behind a flap with screws.
|>
|> That's what we try to clear up...
|
| In use cases where you need external power while on the go with USB,
| you probably wouldn't want to have to disassemble your Neo all the
| time. E.g., I think "backup to external storage" would be a plausible
| use case.

Right.

| Also, how could an "internal" receptacle be placed such that no crazy
| mechanics are needed and the plug doesn't interfere with anything
| else ?

I imagined if the USB socket is like this (B=battery)

s BBB
~  BBB
~  BBB

we could mate to it (c = cable)

s BBB
c BBB
c BBB
c

but I agree external access will be more certain and better and waste
less space.

- -Andy
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