147 lines
4.5 KiB
Markdown
147 lines
4.5 KiB
Markdown
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# RTC (Real Time Clock)
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Setup a good time source. The built in RTC for Allwinner chips lacks a battery on the Orange Pi boards and has a higher drain than others. Go with the others for the better power use
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## Inspiration / Further Reading
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- [https://learn.adafruit.com/adding-a-real-time-clock-to-raspberry-pi?view=all](https://learn.adafruit.com/adding-a-real-time-clock-to-raspberry-pi?view=all)
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- [https://www.raspberrypi.org/forums/viewtopic.php?t=20619](https://www.raspberrypi.org/forums/viewtopic.php?t=20619)
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- [https://www.raspberrypi-spy.co.uk/2015/05/adding-a-ds3231-real-time-clock-to-the-raspberry-pi/](https://www.raspberrypi-spy.co.uk/2015/05/adding-a-ds3231-real-time-clock-to-the-raspberry-pi/)
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- [https://unix.stackexchange.com/questions/246605/how-can-the-link-target-of-dev-rtc-be-changed](https://unix.stackexchange.com/questions/246605/how-can-the-link-target-of-dev-rtc-be-changed)
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- [https://www.raspberrypi.org/forums/viewtopic.php?t=85683](https://www.raspberrypi.org/forums/viewtopic.php?t=85683)
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## Clocks
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### Suggestions
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- Use cheapest for ultra portable builds
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- Use most accurate for mostly permanent builds (RV/similar)
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- Use most common rarely used (unless you have good reason, don't)
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### Hardware
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- [DS1307 (most common | Link)](https://www.adafruit.com/product/3296)
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- [PCF8523 (cheapest | Link)](https://www.adafruit.com/product/3295)
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- [DS3231 (most accurate | Link](https://www.adafruit.com/product/3013)
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### Key Note
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This guide assumes the PCF8523. You'll need to adjust lightly for the DS3231 or DS1307.
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## Initial Setup
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``` bash
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armbian-config # enable i2c busses
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systemctl reboot # reboot to enable bus(es)
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apt install i2c-tools # install tools
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i2cdetect -l # check to ensure busses are present
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i2cdetect -y 0 # 0 for orange pi zero ; 1 for recent pi's
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modprobe rtc-pcf8523 # load the proper rtc module (adafruit cheap model)
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echo pcf8523 0x68 > /sys/class/i2c-adapter/i2c-0/new_device # setup device so it's seen
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dmesg | grep rtc # verify the kernel sees the rtc
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ls /dev/rtc* # should have rtc1
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hwclock -f /dev/rtc1 --systohc -D --noadjfile --utc # set / init the rtc
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hwclock -r -f /dev/rtc1 # read the value from the rtc
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hwclock -w -f /dev/rtc1 # write the current time to the rtc
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apt remove --purge fake-hwclock # purge the fake hwclock as we have a real one now
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```
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## Udev Rules
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``` bash
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# setup udev rule to setup the new rtc as the primary for the board
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# `udevadm info -a -p /sys/class/rtc/rtc1` gets the details for the below entries
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cat > /etc/udev/rules.d/99-rtc1.rules <<EOF
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KERNEL=="rtc1", SUBSYSTEM=="rtc", DRIVER=="", ATTR{name}=="rtc-pcf8523 0-0068", SYMLINK="rtc", MODE="0666"
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EOF
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```
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## Internal RTC Adjustments
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A systemd service to ensure the internal RTC is 'close' to the real time w/o battery.
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``` bash
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# Set the internal RTC on shutdown to match ntpified time
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cat > /etc/systemd/system/rtc0-shutdown-fix.service <<EOF
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[Unit]
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Description=Set sunxi internal RTC on shutdown
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DefaultDependencies=no
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Before=shutdown.target reboot.target halt.target
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[Service]
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Type=oneshot
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ExecStart=/sbin/hwclock --systohc -D --noadjfile --utc -f /dev/rtc0
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[Install]
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WantedBy=halt.target reboot.target shutdown.target
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EOF
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systemctl daemon-reload
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systemctl enable rtc0-shutdown-fix
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# Trick for getting the early boot time 'close'
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cat > /etc/systemd/system/rtc0-online.service <<EOF
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[Unit]
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Description=Set system clock to rtc0
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DefaultDependencies=no
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Before=time-sync.target
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[Service]
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Type=oneshot
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ExecStart=/sbin/hwclock -s -f /dev/rtc0
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[Install]
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WantedBy=time-sync.target
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EOF
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systemctl daemon-reload
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systemctl enable rtc0-online
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```
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## External RTC On Boot
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A systemd unit that brings the external RTC online during boot
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``` bash
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cat > /etc/systemd/system/rtc1-online.service <<EOF
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[Unit]
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Description=Setup rtc1 as primary clock
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DefaultDependencies=no
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Before=time-sync.target
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After=rtc0-online.service
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[Service]
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Type=oneshot
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ExecStart=/bin/sh -c '/sbin/modprobe rtc_pcf8523 \
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&& echo pcf8523 0x68 > /sys/class/i2c-adapter/i2c-0/new_device \
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&& /sbin/hwclock -s -f /dev/rtc1'
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[Install]
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WantedBy=time-sync.target
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After=rtc0-online
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EOF
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systemctl daemon-reload
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systemctl
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```
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## Misc Notes
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``` bash
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date # Wait for this to get sync'd via whatever ntp you're doing
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hwclock -r -f /dev/rtc1 # Verify this isn't right
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hwclock -w -f /dev/rtc1 # Write ntp system time -> rtc
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hwclock -r -f /dev/rtc1 # Verify the write worked
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ls -l /dev/rtc* # Check rtc dev node is present
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hwclock -r -f /dev/rtc1 # read time from external rtc
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hwclock -r -f /dev/rtc0 # read time from internal rtc
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```
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