GSM modem power on/off issues at gta01

Sean Chiang sean_chiang at
Fri Feb 29 05:24:04 CET 2008

HI! list,

Here's my recent observation about the power management of GSM modem 
within gta01,
just a note. If we want to power off GSM modem _completely_ we need to 
issue AT at POFF
to modem and subsequently echo "0" > power_on.

Without AT at POFF, even shutdown the gta01 the battery life still be 
consumed by GSM modem.
My misunderstanding is the GSM modem could be power on/down only one 
time, after you power
off GSM modem, you couldn't power on modem anymore. And I'm wrong, the 
modem could be
powered on|off by echo "1"|"0" > power_on repeatedly.

A wrapper called gsm-pm which is called by init when device on, is used 
to control the on/off GSM modem. gsm-pm will
power on modem then run gsmd. After that, gsm-pm will wait until gsmd is 
killed. When gsm-pm detect the gsmd
was killed it will send "AT at POFF" to modem then echo "0" to power_on.

With this we doesn't need to worry the gsmd is dead or not. I tried to 
write the gsm-pm, could be download from  I still have 
problem when write AT at POFF to modem.

Is this idea ok?

-Sean Chiang

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