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    SubjectDocument sysfs interface to RTC system wakeup
    diff --git a/Documentation/rtc.txt b/Documentation/rtc.txt
    index 8deffcd..ac843ab 100644
    --- a/Documentation/rtc.txt
    +++ b/Documentation/rtc.txt
    @@ -187,6 +187,88 @@ driver returns ENOIOCTLCMD. Some common

    If all else fails, check out the rtc-test.c driver!

    + Even newer /sys interface
    + ~~~~~~~~~~~~~~~~~~~~~~~~~
    +
    +tino.keitel@gmx.de
    +
    +How to use /sys/class/rtc/rtcX/wakealarm
    +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    +This file takes the seconds since epoch to enable a wake event at the
    +specified time.
    +
    +If a '0' is written, the alarm is disabled.
    +
    +If the alarm was already enabled, a new alarm can only be set after the
    +old alarm is disabled.
    +
    +
    +Migration from /proc/acpi/alarm
    +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    +Users of /proc/acpi/alarm have to change their code to supply the
    +seconds since epoch instead of a date string.
    +
    +For shell scripts, this can be done using the date command, e.g. like
    +this:
    +
    +date -d tomorrow "+%s"
    +
    +This returns the seconds since epoch of the current time on the
    +following day.
    +
    +Please note that you have to disable the old alarm first, if you want
    +to set a new alarm. Otherwise, you get an error. Example:
    +
    +echo 12345 > /sys/class/rtc/rtc0/wakealarm
    +echo 0 > /sys/class/rtc/rtc0/wakealarm
    +echo 23456 > /sys/class/rtc/rtc0/wakealarm
    +
    +
    +cd /proc/acpi
    +echo EXP0 > wakeup
    +echo PCI1 > wakeup
    +echo USB0 > wakeup
    +echo USB1 > wakeup
    +echo USB2 > wakeup
    +echo USB7 > wakeup
    +echo HDEF > wakeup
    +cd /sys/class/rtc/rtc0
    +echo $(( $(cat since_epoch) + 20 )) > wakealarm
    +
    + [PATCH] RTC gets sysfs wakealarm attribute
    +
    + This adds a new "wakealarm" sysfs attribute to RTC class devices which support
    + alarm operations and are wakeup-capable:
    +
    + - It reads as either empty, or the scheduled alarm time as seconds
    + since the POSIX epoch. (That time may already have passed, since
    + nothing currently enforces one-shot alarm semantics.)
    +
    + - It can be written with an alarm time in the future, again seconds
    + since the POSIX epoch, which enables the alarm.
    +
    + - It can be written with an alarm time not in the future (such as 0,
    + the start of the POSIX epoch) to disable the alarm.
    +
    + Usage examples (some need GNU date) after "cd /sys/class/rtc/rtcN":
    +
    + alarm after 10 minutes:
    + # echo $(( $(cat since_epoch) + 10 * 60 )) > wakealarm
    + alarm tuesday evening 10pm:
    + # date -d '10pm tuesday' "+%s" > wakealarm
    + disable alarm:
    + # echo 0 > wakealarm
    +
    + This resembles the /proc/acpi/alarm file in that nothing happens when the
    + alarm triggers ... except possibly waking the system from sleep. It's also
    + like that in a nasty way: not much can be done to prevent one task from
    + clobbering another task's alarm settings.
    +
    + It differs from that file in that there's no in-kernel date parser.
    +
    + Note that a few RTCs ignore rtc_wkalrm.enabled when setting alarms, or aren't
    + set up correctly, so they won't yet behave with this attribute.
    +

    -------------------- 8< ---------------- 8< -----------------------------

    --
    (english) http://www.livejournal.com/~pavelmachek
    (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html


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