Disallowing draining until bricking / open++

Andy Green andy at openmoko.com
Fri Jul 18 16:06:24 CEST 2008

Hash: SHA1

Somebody in the thread at some point said:
| 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?



does take care about the logical ON / OFF switch and contains code like

(./arch/arm/plat-s3c24xx/neo1973_pm_gsm.c  gsm_write() ):

						  PCF50633_GPIO2, 1);

and later, ", 0);" which will do the power switch too.

| 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.)

No you're right about GTA01 not having such a discrete power switch
between battery and GSM side.  GTA02 does have this.

|> 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.

I think the intention of it is to power down GSM side in a deep way, but
it is secondary in GTA02 to the fact we can take power away from it already.

In the future I think we would win big by exposing schematics for review
by the community WHILE they are being generated, to really push this
open thing to the next level.  There must be at least half a dozen
errors on GTA02 during various phases of development that "many eyes"
would have found before we made PCBs.  We wouldn't be able to provide
all datasheets due to NDA, but over half of them are in Google anyway.

- -Andy
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