RTC

Introduction

The Core-1126-JD4 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 Core-1126-JD4 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