RTC

Introduction

ROC-RK3506B-CC development BOARD uses TT8563RH as RTC(

Real Time Clock

), TT8563RH is a low power CMOS real-time Clock/calendar chip, it
provides a programmable Clock output, an interrupt Output and a power
down detector, all addresses and data are passed serially through the
I2C bus interface.

Timing can be based on 32.768kHz crystals in seconds, minutes, hours,
weeks, days, months and years

Wide working voltage range :1.0~5.5V

Low resting current: Typical 0.25μA(VDD =3.0V, TA =25°C)

Internal integrated oscillating capacitor

drain open circuit interrupt pin

ROC-RK3506B-CC needs to be connected to the RTC battery to power the
RTC chip to ensure that the RTC can operate normally after a short
system power outage.


Driver RTC

DTS Reference: "kernel/arch/arm/boot/dts/rk3506b-firefly-roc-rk3506b-
cc.dtsi"

Driver Reference: "kernel/drivers/rtc/rtc-hym8563.c"

Interface usage

Linux provides three user-space call interfaces. The corresponding
path in the ROC-RK3506B-CC 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:

   root@rk3506-buildroot:/# cat /sys/class/rtc/rtc0/date
   2021-01-01

   root@rk3506-buildroot:/# cat /sys/class/rtc/rtc0/time
   17:18:14

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

Attention: ROC-RK3506B-CC not support scheduled power-on.

PROCFS Interface

Print RTC related information:

   root@rk3506-buildroot:/# cat /proc/driver/rtc
   rtc_time        : 17:20:04
   rtc_date        : 2021-01-01
   alrm_time       : 16:31:00
   alrm_date       : 2021-01-02
   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 instructions, please refer to the document
"kernel/Documentation/admin-guide/rtc.rst".

FAQs

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

A1 :

  Check that the RTC battery is properly connected