Add wakealarm description to rtc.txt, now including comments from Michael and others. Signed-off-by: Pavel Machek <pavel@xxxxxxx> --- clean-cg/Documentation/rtc.txt 2008-02-07 10:28:47.000000000 +0100 +++ linux/Documentation/rtc.txt 2008-12-09 13:51:06.000000000 +0100 @@ -187,6 +187,64 @@ If all else fails, check out the rtc-test.c driver! + Even newer /sys interface + ~~~~~~~~~~~~~~~~~~~~~~~~~ + (thanks to tino.keitel@xxxxxx) + +How to use /sys/class/rtc/rtcX/wakealarm +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ +This file can be used to view / set the time of an alarm (wakeup event). The +contents of the file are time measured in seconds since the Epoch +(00:00:00h, 1 Jan 1970, UTC). + + - 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. + +If the alarm was already enabled, a new alarm can only be set after the +old alarm is disabled. + + 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. + + + +Migration from /proc/acpi/alarm +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ +Users of /proc/acpi/alarm have to change their code to supply the +seconds since the Epoch instead of a date string. (The date string in +/proc is quite and ugly hack, and it will be removed one day, with +rest of /proc/acpi). + +For shell scripts, this can be done using the date command, e.g. like +this: + +date -d tomorrow "+%s" + +This returns the seconds since the 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: + +# Toggle example wakeup devices. Be sure to do 'cat wakeup' to check +# the status when you are done. +cd /proc/acpi +echo EXP0 > wakeup +echo PCI1 > wakeup +echo HDEF > wakeup +cd /sys/class/rtc/rtc0 +echo 0 > wakealarm +echo $(( $(cat since_epoch) + 20 )) > wakealarm + -------------------- 8< ---------------- 8< ----------------------------- -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html