[Gumstix-users] RTC only sync'ed on normal shutdown

[General m. l. f. g. users. <gum...@li...>]

I'm having issues with real-time clock synchronization on a gumstix air (or
fire) storm.  It's possible that this is a more general Linux issue.

If I set the date (date -s ... or ntpdate), then write to hwclock:
hwclock -w  (or hwclock --systohc)

and shutdown normally:
shutdown -h now

when I reboot, the rtc reflects what I set the date/time to.  However, if I
shut down by loss of battery or sending the GPIO kill signal I have, it does
not.  Sending the GPIO kill signal is our normal way to shut down.  So, our
rtc is almost never updated even if I execute:
hwclock -w

I've also tried doing:
hwclock -w
sync

That doesn't do any good either.  In either case, if I read via hwclock, the
value reflects my change, but won't survive an "abnormal" shutdown.

It appears that the data is being cached and something in the normal
shutdown process causes that cache to be written out to the device itself. 
I looked at the busybox hwclock code (which is what I'm using).  It writes
to /dev/rtc which is sym linked to /dev/rtc0.

Can anyone tell me how to force a write to the RTC?  Put differently, what
is the normal shutdown process doing that causes the update to truly be made
to the RTC?

Thanks.



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