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