RTC¶

Introduction¶

AIBOX-Orin Nano has an external RTC powered by a capacitor on the external motherboard, which ensures the RTC continues to run for a short period after power loss. In the kernel, it is represented as rtc0.

Interface Usage¶

Linux provides three user-space interfaces for interacting with the RTC. The paths are:

SYSFS interface: /sys/class/rtc/rtc0/
PROCFS interface: /proc/driver/rtc
IOCTL interface: /dev/rtc0

Synchronize the current system time to the RTC.

hwclock -w

SYSFS interface¶

You can directly use cat and echo to operate the interfaces under /sys/class/rtc/rtc0/.

For example, to view the current RTC date and time:

# cat /sys/class/rtc/rtc0/date
2024-07-10
# cat /sys/class/rtc/rtc0/time
02:36:30

PROCFS interface¶

To print RTC-related information:

# cat /proc/driver/rtc
rtc_time        : 02:37:00
rtc_date        : 2024-07-10
alrm_time       : 00:00:00
alrm_date       : 1970-01-01
alarm_IRQ       : no
alrm_pending    : no
update IRQ enabled      : no
periodic IRQ enabled    : no
periodic IRQ frequency  : 1
max user IRQ frequency  : 64
24hr            : yes

IOCTL interface¶

You can use ioctl to control /dev/rtc0。

For detailed usage instructions, please refer to document kernel-jammy-src/Documentation/admin-guide/rtc.rst 。