Messages in this thread | | | Date | Fri, 28 Nov 2008 16:49:16 -0500 | From | "Michael Kerrisk" <> | Subject | Re: Document sysfs interface to RTC system wakeup |
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Pavel,
Some comments and suggestions below.
On Wed, Nov 26, 2008 at 11:15 AM, Pavel Machek <pavel@suse.cz> wrote: > 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.
Better:
This file can be used to view / set the time of a wakeup event. The contents of the file are time measured in seconds since the Epoch (00:00:00h, 1 Jan 1970, UTC).
> + > +If a '0' is written, the alarm is disabled.
Now -- you started off talking about a "wake event" and now you switched to talking about an "alarm" -- which is it? Be consistent.
> + > +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.
As Jonathan said -- if I'm using /proc/acpi/alarm, why do I care? What advantages does the new interface provide for me that would motivate me to change?
> +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
s/epoch/the Epoch/
> +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
Here, it might be useful to show an example of an error. E.g., if one does these commands instead, show the error from the second command:
echo 12345 > /sys/class/rtc/rtc0/wakealarm echo 23456 > /sys/class/rtc/rtc0/wakealarm echo 0 > /sys/class/rtc/rtc0/wakealarm echo 34567 > /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
s/epoch/Epoch/ (and other instances below)
> + 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.
The last sentence is garbled -- bad grammar/missing words -- somewhere near "or aren't".
Cheers,
Michael
-- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ git://git.kernel.org/pub/scm/docs/man-pages/man-pages.git man-pages online: http://www.kernel.org/doc/man-pages/online_pages.html Found a bug? http://www.kernel.org/doc/man-pages/reporting_bugs.html
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