[Bug 1289] PSC (power saving commands in muxer mode) seems to be broken

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http://bugzilla.openmoko.org/cgi-bin/bugzilla/show_bug.cgi?id=1289





------- Additional Comments From zecke at selfish.org  2008-03-28 05:57 -------
GSM 07.10 is pretty clear in this respect (5.4.7):

"""
If either TE or MS wishes to enter a low-power state a power saving control
command message is sent to the other station on the multiplexer control channel.
The station receiving the message will complete the transmission of any
frames in progress, report a busy or power-down condition to higher layers,
freeze all timers and transmit the power saving control response message. When
the station that initiated the power saving control message receives the
acknowledgement it is then free to enter the reduced-power state.
"""

Yes, the modem would have to send something before going to (deep) sleep, it
doesn't, a violation to the spec. But honestly I think this is no big deal. I
don't remember seeing this on Wavecom (well they use their own multiplexer
format) and Siemens modules.



"""
Either station may send a power saving control command requesting that the other
station enters a low power state. The responding station must acknowledge this
command with a power saving control response message but need not obey the
command to enter a low-power state. If no response is received the commanding
station may repeat the command but must first use the wake-up procedure.
"""

This is the GSM stack on the host requesting the modem to sleep, I have seen a
variation of this on Siemens multiplexers. From a small chat with Sean Chiang
the modem is doing its own (deep) sleep, so sending this message is not
necessary (from what I understand). E.g. even if the modem would not respond to
these PSC, I think I wouldn't say there is much to fix. An obvious spec
violation but if we save power I think it is fine.


You should file a separate bug on the losing of frame and failing resync? From
what I have heard from Sean Chiang, the modem will drop/lose the first bytes
sent to the uart after a deep sleep, this is a hardware shortcoming. This means
the modem receives a frame without the sync/start flag/byte, which is by
definition invalid. The question is: Will it resync properly? Will it resync at
some point? I will try to do some tests myself, but please file a separate bug
on this issue. I think it is the only one to research and fix.



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