8. RTC¶

8.1. 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.

_images/usage_rtc_battery.jpg

8.2. Driver RTC¶

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

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

8.3. 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

8.3.1. 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:

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.

8.3.2. 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

8.3.3. IOCTL Interface¶

You can use ioctl to control /dev/rtc0.

For detailed instructions, please refer to the document kernel/Documentation/admin-guide/rtc.rst.

8.4. FAQs¶

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

A1 : Check that the RTC battery is properly connected