Y-cable and USB-OTG: mutually exclusive

Andy Green andy at openmoko.com
Tue Apr 29 09:49:27 CEST 2008

Hash: SHA1

Somebody in the thread at some point said:

| Yea, but "keep it simple" not exactly means you have to open the case to
| insert a connector to debug port (now GTA04 can't lie flat on desk
| anymore, because debug is on backside), just to apply power when sth
| like a WiFi stick, USB-memstick, USB-drive... etc is connected to GTA.

Just saying that if the debug USB connector can do double duty as
"adapter power" that makes everyone happy.  It doesn't have to be in a
place that stops thing lying on desks.

| Confusion of end-user by 2 identical connectors, one of them, the really
| hard to find one, for (virtually everyday) power for host mode and
| useful for nothing else but (highly sophisticated) debug, the other for
| power *only* when not in OTG-mode, but you can do everything else with
| it... :-/
| My 0.02EUR: A no-go, a no-NO-go. The appeal of simplicity of a coax
| power connector you probably find 10000 times more "chargers" for it
| everywhere in he world than for USB (e.g. my old nokia charger), you
| simply can't beat that.

Power isn't the only consideration, we already thought about bringing
out debug USB connector to the outside world.  If that is what we do,
then it is sitting there ready to eat power the same as the OTG
connector, and it makes sense to allow it.  It is a built-in solution
for what the Y cable is proposed to do.

Confusion can be managed by recessing the connector slightly, putting it
somewhere less obvious, marking them differently, etc.  But it will need
to be managed.

|> The pcf50633 also has this "adapter" concept that we should look at
|> deploying for debug USB power input, it's not used in GTA02, that'd be
|> pretty neat.
| Yep, but know what: I just can't find it anymore, anywhere in the
| datasheets (50633|50606), in circuit diagrams of GTA01/02... nowhere :-(
| Already started to doubt my own memory. Wasn't there a ting like
| 'charging 1A only via power-adapter, USB can only do 500mA'??? Some FET
| aso? Swear I seen this some months ago...

It's supported with external FET directly to this SYS rail, but there
are facilities for detecting presence and controlling this FET.  See Fig
61 / p118 ADAPTSNS / ADAPTCTRL on PCF50633UM2.00.pdf for example

| Anyway, we may hook up as many power rails as we like, just decoupling
| them and testing individually (A/D) for voltage.

It's much better if the PMU knows about it and treats it as a case it
understands, which we can have here with "adapter".

- -Andy
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