86 lines
2.6 KiB
Markdown
86 lines
2.6 KiB
Markdown
# Real Time Clock (RTC)
|
|
|
|
Helios64 has an on-board RTC clock which is provided by the Power Management IC (PMIC) RK808-D. The RTC functions provided by the PMIC include second/minute/hour/day/month/year information, alarm wake up as well as time calibration.
|
|
|
|
|
|
|
|
The SoC receive clock signal from the PMIC RTC and in the meantime access the PMIC RTC functions over I2C bus.
|
|
|
|
## RTC Battery
|
|
|
|
To save time information and allow the RTC to keep running while system is powered off, the PMIC RTC relies on a dedicated coin battery located at BAT1. The battery holder (BAT1) accepts CR1225 battery model.
|
|
|
|
!!! Note
|
|
The polarity of the battery holder is indicated on the PCB with **'+'** signs.
|
|
|
|
|
|
|
|
However if your setup has the [UPS](/helios64/ups/) battery connected, then RTC battery is not required since the RTC clock can also be kept powered by the UPS battery.
|
|
|
|
## Scheduled Power On using RTC
|
|
|
|
User can set up a scheduled power on using RTC alarm.
|
|
|
|
### Use SYSFS
|
|
|
|
Run following command to check whether there is any alarm set,
|
|
|
|
```bash
|
|
cat /sys/class/rtc/rtc0/wakealarm
|
|
```
|
|
If nothing return, it means no alarm set.
|
|
|
|
To reset/disable the alarm, run:
|
|
|
|
```bash
|
|
echo 0 | sudo tee /sys/class/rtc/rtc0/wakealarm
|
|
```
|
|
|
|
The alarm only accepts Unix epoch time. We can use *[date](https://linux.die.net/man/1/date)* utility as helper to get epoch time of our calendar.
|
|
|
|
To set alarm from absolute calendar time, run:
|
|
|
|
```bash
|
|
echo `date '+%s' -d '20 December 2020 02:14:10 PM'` | sudo tee /sys/class/rtc/rtc0/wakealarm
|
|
```
|
|
You can also set alarm from relative time using this command:
|
|
|
|
```bash
|
|
echo `date '+%s' -d '+ 1 hour 2 minutes 10 seconds'` | sudo tee /sys/class/rtc/rtc0/wakealarm
|
|
```
|
|
|
|
After alarm set, you can power off the system and keep the power plugged in. Helios64 should automatically power on at the scheduled time.
|
|
|
|
### Use rtcwake
|
|
|
|
Run following command to check whether there is any alarm set:
|
|
|
|
```bash
|
|
sudo rtcwake -m show
|
|
```
|
|
|
|
To reset/disable the alarm, run:
|
|
|
|
```bash
|
|
sudo rtcwake -m disable
|
|
```
|
|
|
|
To set alarm from absolute calendar time, run:
|
|
|
|
```bash
|
|
sudo rtcwake -m off --date '2020-12-20 14:14:10'
|
|
```
|
|
|
|
You can also set alarm from relative time using this command:
|
|
|
|
```bash
|
|
sudo rtcwake -m off --date '+ 1 hour 2 minutes 10 seconds'
|
|
```
|
|
|
|
After the command successfully executed, system will shutdown. Keep the power plugged in and Helios64 should autommatically power on at the scheduled time.
|
|
|
|
## References
|
|
|
|
[date- Linux manual page](https://linux.die.net/man/1/date)
|
|
|
|
[rtcwake - Linux manual page](https://linux.die.net/man/8/rtcwake)
|