6. RTC

6.1. Introduction

AIO-3576JD4 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

AIO-3576JD4 has a capacitor to supply power to the RTC as shown in the following figure to ensure that the RTC runs in a short time.

_images/usage_rtc_capacitor.jpg

6.2. Driver RTC

DTS Reference: kernel/arch/arm64/boot/dts/rockchip/rk3576-firefly-aio-3576jd4.dtsi

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

6.3. Interface usage

Linux provides three user-space call interfaces. The corresponding path in the AIO-3576JD4 development board is:

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

  • PROCFS Interface : /proc/driver/rtc

  • IOCTL Interface : /dev/rtc0

6.3.1. 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

Attention: AIO-3576JD4 not support scheduled power-on.

6.3.2. 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

6.3.3. IOCTL Interface

You can use ioctl to control /dev/rtc0.

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

6.4. FAQs

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

A1 : Check that the RTC battery is properly connected