RTC

OpenNMC includes a DS3232MZ+ real-time clock with battery backup.

Devices

Device	Notes
/dev/rtc0	DS3232MZ+ over I2C with external battery backup
/dev/rtc1	SoC RTC, enabled but not the default RTC

Battery

The RTC uses a replaceable CR1220 battery in a slide-in holder.

Verify Detection

cat /sys/class/rtc/rtc0/device/name

Expected output:

ds3232

Read And Write Time

Write system time to the RTC:

hwclock -w -f /dev/rtc0

Read time back from the RTC:

hwclock -r -f /dev/rtc0

Battery Check

Power the system down, wait, and boot again to confirm that the clock continued running.