86 lines
2.4 KiB
Markdown
86 lines
2.4 KiB
Markdown
# Real Time Clock (RTC)
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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.
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The SoC receive clock signal from the PMIC RTC and in the meantime access the PMIC RTC functions over I2C bus.
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## RTC Battery
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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.
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!!! Note
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The polarity of the battery holder is indicated on the PCB with **'+'** signs.
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## Scheduled Power On using RTC
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User can set up a scheduled power on using RTC alarm.
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### Use SYSFS
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Run following command to check whether there is any alarm set,
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```bash
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cat /sys/class/rtc/rtc0/wakealarm
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```
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If nothing return, it means no alarm set.
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To reset/disable the alarm, run
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```bash
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echo 0 | sudo tee /sys/class/rtc/rtc0/wakealarm
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```
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The alarm only accept Unix epoch time. We can use *[date](https://linux.die.net/man/1/date)* utility as helper to get epoch time of our calendar.
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To set alarm from absolute calendar time, run
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```bash
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echo `date '+%s' -d '20 December 2020 02:14:10 PM'` | sudo tee /sys/class/rtc/rtc0/wakealarm
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```
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You can also set alarm from relative time using this command,
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```bash
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echo `date '+%s' -d '+ 1 hour 2 minutes 10 seconds'` | sudo tee /sys/class/rtc/rtc0/wakealarm
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```
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After alarm set, you can power off the system and keep the power plugged in. Helios64 should automatically power on at the scheduled time.
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### Use rtcwake
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Run following command to check whether there is any alarm set,
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```bash
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sudo rtcwake -m show
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```
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To reset/disable the alarm, run
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```bash
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sudo rtcwake -m disable
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```
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To set alarm from absolute calendar time, run
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```bash
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sudo rtcwake -m off --date '2020-12-20 14:14:10'
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```
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You can also set alarm from relative time using this command,
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```bash
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sudo rtcwake -m off --date '+ 1 hour 2 minutes 10 seconds'
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```
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After the command successfully executed, system will shutdown. Keep the power plugged in and Helios64 should autommatically power on at the scheduled time.
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## References
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[date- Linux manual page](https://linux.die.net/man/1/date)
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[rtcwake - Linux manual page](https://linux.die.net/man/8/rtcwake)
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