RTC
Introduction
ROC-RK3568-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 400 Kbits/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 0.25 μA(VDD = 3.0V, TA = 25°C)
- Internal integrated oscillating capacitor
- Drain open circuit interrupt pin
Interface usage
Linux provides three user-space call interfaces. The corresponding path in the ROC-RK3568-PC development board is:
- SYSFS Interface:
/sys/class/rtc/rtc0/ - PROCFS Interface:
/proc/driver/rtc - IOCTL Interface:
/dev/rtc0
SYSFS Interface
You can directly use cat and echo to operate the interfaces under /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
09:36:10Set 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 -pPROCFS 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 : yesIOCTL 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.