sysfs Interface

The interface only supports setting on the following two parameters:

• wakealarm: Run the following command to set a wakeup alarm in X seconds since the current RTC time.

  echo ‘+X’ > /sys/class/rtc/rtc0/wakealarm 

  Note:

  • The interface is Linux original and the alarm is set in seconds. For example, to set an alarm which rings after 2 hours, use the following command:

    echo ‘+7200’ > /sys/class/rtc/rtc0/wakealarm 

  • The minimum alarms unit supported by the RTC alarm register is in minutes. If it is less than 1 minute, the next minute is used as the alarm time. For example, if the current time is 09 : 00 : 45, the example command should be:

    echo ‘+30’ > /sys/class/rtc/rtc0/wakealarm

    So, the time to trigger alarm should be 09 : 02 : 00.
• offset: Used to calibrate the time offset caused by temperature and oscillator. Not recommended to use in the current product release.

The following code block shows a simple example.

# cd /sys/class/rtc/rtcO/ 
# ls 
alarmtimer.0.auto        hctosys            range            uevent
date                     max_user_freq      since_epoch      wakealarm
dev                      name               subsystem
device                   offset             time
# cat date 
2001-02-01 
# cat time 
00:23:57