RTC

Introduction

Face-RK3399 development board has an RTC (Real Time Clock) integrated
into the RK808. The main functions are clock, calendar, alarm clock,
periodic interrupt, dual channel 32KHz clock output.

After

J2

 is connected with

CR2032

 button battery, it can ensure that the RTC can run normally after the
board power down.

After Face-RK3399 V2, RTC uses "hym8563" external RTC chip which run
in i2c7 bus. There is farad capacitor on the board for power
consumption.

RTC drive

DTS configuration information is stored on the rk808 node.

Driver code path: drivers/rtc/rtc-rk808.c

V2 Driver code path: drivers/rtc/rtc-hym8563.c

Interface usage

Linux provides three user-space interfaces. The corresponding path in
the Face-RK3399 development board is:

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

PROCFS Interface: /proc/driver/rtc

IOCTL Interface: /dev/rtc0

SYSFS Interface

You can operate the interfaces in "/sys/class/rtc/rtc0/" by "cat" and
"echo" command directly.

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 up after 120 seconds
   echo +120 >  /sys/class/rtc/rtc0/wakealarm
   # View boot time
   cat /sys/class/rtc/rtc0/wakealarm
   # Power off
   reboot -p

PROCFS Interface

Print RTC related information:

   # cat /proc/driver/rtc
   rtc_time        : 09:34:59
   rtc_date        : 2013-01-18
   alrm_time       : 08:52:45
   alrm_date       : 2013-01-18
   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".

Please refer to the document "rtc.txt" for more details.

FAQs

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

A1 :

 Check that the RTC battery is properly connected.