RTC

Introduction

AIBOX-3576 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" 。