How does one return the GSM modem to a known state?

Mike (mwester) mwester at
Thu Nov 1 03:51:23 CET 2007

I'm looking for a way to have a function within the kernel issue the
required sequence to power off the GSM modem on the GTA01 when Linux shuts

How can one return the GSM modem on the GTA01 to a known state from which it
can be issued the AT at POFF command to power itself off?  The reset GPIO is
not connnected on the GTA01, and the power GPIO only turns it on, does not
turn off the modem -- so as far as I know, one must be able to issue the AT
command to power off -- otherwise the device is powered off, but the phone
remains on and fully functional (a clear violation in many situations, such
as blast zones, or aircraft).

We need to assume that the modem can be in *any* state when the shutdown
needs to be issued, hence the need to return it to a mode where it will
accept and act on an AT command immediately.

Is there a magic sequence for this?  Or can I just assume that issuing
something like \r\rAT at POFF\r will *always* work?

Mike  (mwester)

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