9. RTC

9.1. Introduction

ROC-RK3566-PC 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

9.2. RTC驱动

The dts configuration reference in the Android SDK: kernel/arch/arm64/boot/dts/rockchip/rk3566-roc-pc.dtsi

&i2c2 {
    status = "okay";
    hym8563: hym8563@51 {
		status = "okay";
		compatible = "haoyu,hym8563";
		reg = <0x51>;
		#clock-cells = <0>;
		rtc-irq-gpio = <&gpio0 RK_PC1 IRQ_TYPE_EDGE_FALLING>;
		clock-frequency = <32768>;
		//clock-output-names = "xin32k";
		/* rtc_int is not connected */

9.3. Interface usage

Linux provides three user-space call interfaces. The corresponding path in the ROC-RK3566-PC development board is:

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

  • PROCFS Interface : /proc/driver/rtc

  • IOCTL Interface : /dev/rtc0

9.3.1. 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
# cat /sys/class/rtc/rtc0/time

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

9.3.2. 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

9.3.3. IOCTL Interface

You can use ioctl to control /dev/rtc0.

Please refer to the document kernel/Documentation/rtc.txt for detailed instructions.

9.4. FAQs

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

A1 : Check that the RTC battery is properly connected