Real Time Clock (RTC)¶
Setting the RTC¶
Please note that starting from kernel 5.x the RTC node in the device tree must not include the IRQ pin declaration if it is not actually connected. If a wrong declaration is present the hwclock command will fail.
First set the system date & time:
Then set the HW RTC using the system date & time:
Power down your board, wait 5 minutes and power up again, then check you system date & time and verify it is correct:
Wakeup using the RTC¶
All Variscite EVKs mount RTC ISL12057, however wakeup using the RTC requires hardware connection of ISL12057 IRQ2# pin to a SoC GPIO. By default, the defconfig of latest kernels already enable the Intersil ISL12057 driver. The kernel configuration item is available in Device Drivers -> Real Time Clock -> <*> Intersil ISL12057.
For VAR-SOM-MX8X on Symphony-Board, RTC IRQ#2 pin is not connected: RTC has no wakeup capabilities.
Using rtcwake command¶
Assuming the your board implement RTC wakeup capabilities, ensure RTC and system time are synchronized
then set the RTC to wakeup after 10 seconds type:
echo enabled > /sys/class/rtc/rtc0/device/power/wakeup
echo `date "+%s" -d "+ 10 seconds"` > /sys/class/rtc/rtc0/wakealarm
and immediately suspend the machine