Questions regarding the wakeup interrupt

andrzej zaborowski balrogg at
Wed Mar 26 23:16:55 CET 2008


On 26/03/2008, Holger Freyther <zecke at> wrote:
>  I have started to look into suspend and resume and wonder how the modem wake
>  up is supposed to work in the big plot.
>  Current State:
>         - Enable the modem, enter pin, register with network
>         - Enable unsolicited messages (signal strength, registration...)
>         - echo "mem" > /sys/power/state at any point in time
>         => the device will wake up shortly afterwards due the modem wakeup interrupt.
>  What I would like to know:
>         - How is the modem wakeup pin supposed to work (what makes the modem do the
>  interrupt, what happens in regard to flow control)?
>         - Should the GSM stack disable unsolicited messages before going to sleep?
>         - This would require the GSM stack to know about suspend/resume, so the
>  command queue could be frozen, the last commit submitted, unsolicited
>  messages disabled... but we do not want to go this way.

I'm afraid there is no way around making the GSM stack power-state
conscious, because responses sent from the modem while the CPU was
asleep confuse the serial logic.

Note though that (I think) Sean Chiang can program the modem to drive
the interrupt pin exactly how the GSM stack needs it (before shipping
obviously), so we're not limited to what logic TI has predicted for

>         - How to make the modem wakeup pin usable?

Also note that if only the SMS and incoming call notifications are
left enabled, even the serial data pins could be used as the wake-up

Ideally though (imho) in the future D-Busified gsmd design, gsmd
should subscribe for cell change or signal strength unsolicited
responses from the modem *only* if there are d-bus clients present
subscribed for those notifications, and unsubscribe as soon as such
client apps disconnect. Then we can maybe reach a point where the
signal strength applet / other applets unsubscribe from these
notifications automatically on suspend, but the dialer keeps listening
for incoming call / SMS notification, and as a result gsmd corrently
leaves only exactly these unsolicited resopnses enabled without
knowing anything about power states.

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