[Gta04-owner] Modem is not reset when GTA04 is powered off

Dr. H. Nikolaus Schaller hns at goldelico.com
Mon Mar 5 23:06:56 CET 2012

Am 05.03.2012 um 23:00 schrieb Andreas Kemnade:

> On Mon, 05 Mar 2012 21:11:51 +0000
> Hi,
> Neil Jerram <neil at ossau.homelinux.net> wrote:
>> - In theory, if the system crashed and/or the kernel did not shut down
>>  cleanly (- which is something I've never yet seen -) such that the
>>  GPIO was not toggled, the modem could be left powered on, even with
>>  much of the rest of the phone looking "off".
> Hmm, what about keeping that gpio in a state such the modem
> should be switched off if it is set to low (which happens
> automatically if the rest of the phone is off.

Unfortunately not. The logic definition is:

make it low for >200 ms to switch it on if it is off
make it low to switch of the PA (like airplane mode) and releasing (pull-up) to switch of off if it is on

So it is an impulse that toggles between on and off. But yes, the CPU can find out the state through the USB bus (lsusb will show it).

> so for turning on do something like this (pseudocode):
> gpio186=1
> if (!option_usb_exists_after_timeout()) {
>  gpio186=0;
>  delay();
>  gpio186=1;
>  delay(); // here it should appear
>  gpio186=0;
>  delay();
>  gpio186=1
> }

We do something similar to check if the modem works correctly during function test after production.


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