| 1 |
On Sun, Jan 10, 2016 at 02:55:57PM +0100, Meino.Cramer@×××.de wrote |
| 2 |
> Hi, |
| 3 |
> |
| 4 |
> currently I am experimenting with a new embedded system |
| 5 |
> (OrangePI PC). I want to suspend the system to RAM. |
| 6 |
> After a period of time the system should wakeup. |
| 7 |
> |
| 8 |
> The RTC on the board seems to support alarms. |
| 9 |
> |
| 10 |
> Is there a tool to set the alarm time of an RTC |
| 11 |
> from the commandline like hwclock set the RTC |
| 12 |
> time itsself? |
| 13 |
> |
| 14 |
> I couldn't find one (or successfully overlooked it...) |
| 15 |
> |
| 16 |
> Thank you very much in advance for any help! |
| 17 |
> Best regards, |
| 18 |
> Meino |
| 19 |
|
| 20 |
I'm not aware of any utilities. Is it linux, and how good are you at |
| 21 |
shell scripts? Two virtual files you'll need to know about are... |
| 22 |
|
| 23 |
/sys/class/rtc/rtc0/since_epoch |
| 24 |
/sys/class/rtc/rtc0/wakealarm |
| 25 |
|
| 26 |
Note that writing to /sys requires root privileges. Both files are in |
| 27 |
seconds since 1970-01-01 00:00:00 UTC. This is the same output that |
| 28 |
"date +%s" produces. To test it, run the command... |
| 29 |
|
| 30 |
date +%s ; cat /sys/class/rtc/rtc0/since_epoch |
| 31 |
|
| 32 |
Let's say that you want it wake up in 3 minutes (i.e. 180 seconds from |
| 33 |
now). You'll have to use either "eval" or backticks. The command |
| 34 |
would be... |
| 35 |
|
| 36 |
#!/bin/bash |
| 37 |
echo $(( 180 + `cat /sys/class/rtc/rtc0/since_epoch` )) > /sys/class/rtc/rtc0/wakealarm |
| 38 |
|
| 39 |
...and powerdown. It should wake up 3 minutes after you issued the |
| 40 |
command. |
| 41 |
|
| 42 |
How about specifying a future time, you ask? First, we need to know |
| 43 |
the input format. The "--date" command uses the format |
| 44 |
"MM/DD/YYYY HH:mm:ss" (Month/Day/Year Hour:Minute:Second) |
| 45 |
the brackets indicate optional items. To get the seconds since epoch at... |
| 46 |
|
| 47 |
year 2016 |
| 48 |
month 01 |
| 49 |
day 20 |
| 50 |
hour 23 |
| 51 |
minute 00 |
| 52 |
second 00 |
| 53 |
|
| 54 |
the command is... |
| 55 |
|
| 56 |
date +%s --date="01/20/2016 23:00:00" |
| 57 |
|
| 58 |
...which outputs 1453348800 |
| 59 |
|
| 60 |
To set a wakeup alarm for that time... |
| 61 |
|
| 62 |
date +%s --date="01/20/2016 23:00:00" > /sys/class/rtc/rtc0/wakealarm |
| 63 |
|
| 64 |
You'll probably want to write a script to accept input from a user or |
| 65 |
another program. Beware of UTC offsets and Daylight Saving Time. |
| 66 |
|
| 67 |
-- |
| 68 |
Walter Dnes <waltdnes@××××××××.org> |
| 69 |
I don't run "desktop environments"; I run useful applications |
Archives