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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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