Disallowing draining until bricking

Mike (mwester) mwester at dls.net
Fri Jul 18 15:47:41 CEST 2008

Andy Green wrote:
> Hash: SHA1
> Somebody in the thread at some point said:
> | I've been hoping someone else would mention this, but since nobody has,
> | I guess I'll have to:
> |
> | What about the GSM?
> |
> | We can't power it off from the kernel.
> Well we have two different ways to turn it off, U1705 is a MOSFET switch
> to control if GSM logic can have battery power on VBAT net, it's
> controlled by PMU GPIO 2.  Only the Power Amplifier U201 has a separate
> connection to the battery, but its enable is controlled by the GSM logic
> side and sits low when that is depowered (checked it myself recently).

This hardware was mentioned recently; there's nothing in the kernel that
actually does this (I checked at the time), so I'm unclear as to
what/how this actually works with the GSM.  Can someone unequivocally
state that turning off U1705 is the exact equivalent of issuing AT at POFF
to the GSM?  Or does it do something else/less/more?

Also, just for the record, no such hardware logic exists on the GTA01.
If this statement is incorrect, please correct me!  (This means that the
code and specific techniques implemented for the GTA02 as discussed on
this thread can not apply to the GTA01.)

> Secondly there is logical "on switch" called PWON on U1002, it's driven
> by NPN transistor Q1000 which in turn is controlled by CPU GPIO GPB7.

This is just the "push button" (as Werner called it) to turn it on or
reset it; AFAIK this cannot power the GSM off.  But if U1705 can do
that, then at least on the GTA02 we don't need to worry about this GPIO
at shutdown.

> So I think it is OK.

Well, at least for the GTA02.  Sucks for the GTA01, though. :(

> - -Andy

Mike (mwester)

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