RTC

Introduction

AIO-3568J development BOARD uses HYM8563 as RTC(

Real Time Clock

), HYM8563 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.The maximum bus speed is 400Kbits/s, after each read
and write data, the embedded word address register will automatically
increment

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

RTC驱动

Interface usage

Linux provides three user-space call interfaces. The corresponding
path in the AIO-3568J 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        : 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 "kernel/Documentation/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