RTC

Introduction

The C40PL development board uses RK808 as the RTC (

Real Time Clock

). RK809 integrates a crystal oscillator buffer and a real-time clock
(RTC). The buffer is used in conjunction with an external 32.768kHz
crystal oscillator. With the RTC function, the PMIC can provide
seconds/minutes/hours/days/months/years information, alarm wake-up,
and time calibration. RK817 provides a 32.768kHz clock with an open-
drain output, which is turned on by default and controlled through the
I2C interface.

Driver RTC

Driver Reference: "kernel/drivers/rtc/rtc-rk808.c"

Interface usage

Linux provides three user-space call interfaces. The corresponding
path in the C40PL development board is:

SYSFS Interface : /sys/class/rtc/rtc0/

PROCFS Interface : /proc/driver/rtc

IOCTL Interface : /dev/rtc0

SYSFS Interface

You can directly use the interface below "cat" and "echo" operations
"/sys/class/rtc/rtc0/".

For example, check the date and time of the current RTC:

   # cat /sys/class/rtc/rtc0/date
   2013-01-18
   # cat /sys/class/rtc/rtc0/time
   09:36:10

Set the startup time, such as starting up after 120 seconds:

   #Start the machine regularly after 120 seconds
   echo +120 >  /sys/class/rtc/rtc0/wakealarm
   # View boot time
   cat /sys/class/rtc/rtc0/wakealarm
   #To turn it off
   reboot -p

PROCFS Interface

Print RTC related information:

   # cat /proc/driver/rtc
   rtc_time        : 06:53:50
   rtc_date        : 2022-06-21
   alrm_time       : 06:55:05
   alrm_date       : 2022-06-21
   alarm_IRQ       : yes
   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".

Please refer to the document "rtc.txt" for detailed instructions.

FAQs

Q1: The time is out of sync after the development board is powered on
?

A1 :

  Check that the RTC battery is properly connected