GSM Power off

Paul Fertser fercerpav at
Mon Feb 23 19:54:52 CET 2009

Michael <betheg at> writes:
> can somebody please explain me the differents of these 
> 	- echo 0 >/sys/bus/platform/devices/neo1973-pm-gsm.0/power_on

This depends on kernel version and on GTA0x revision. On all public
GTA02 revisions it cuts the power to the modem, but see below.

> 	- s3c24xx-gpio b7=0

This is usually does nothing interesting. The thing is that MODEM_ON
is literally a push-button for turning on the modem when it's already
powered. So after you physically connect power to the modem you has to
set MODEM_ON to 1, wait for like 0.5 sec, then you should set it back
to 0 (deprees push-button). That was abused by the kernel up until
now, because it set it to 1 on powering and kept it until powering

You can also wonder about modem reset line, but it's not connected on
GTA02 anyway, so this has no effect.

As to physically powering the modem, it depends on GPIO2 PMU
(PCF50633) output, when it is set to 0, the power to the modem is cut.

One funny thing also worth mentioning. Before powering off the modem
one needs to change to input the GPIOs connected to the modem, or else
it will drain some considerable amount of power through that. So if
you want to do it yourself (and you need to if you don't use
andy-tracking 8df75a337131d835d4dd8509696d684e4fa8970e or later), then
use gpio utility to set H1 and H2 to input. 

> 	- echo "AT at POFF" >/dev/ttySAC0

This is supposed to ask modem firmware to power off itself. Was
necessary because GTA01 has no physical power switch. I don't know
exact results of this command though.

Be free, use free ( software!
mailto:fercerpav at

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