Setup Hardware Clock (RTC) Module on a Raspberry Pi

2023-02-04T14:45:37Z

Holesond: /* Install Software */

= Install Hardware =

I used a [http://www.piface.org.uk/products/piface_clock PiFace Real Time Clock]. After installing the CR1220 battery and correctly mounting on the board, [http://www.piface.org.uk/assets/piface_clock/PiFaceClockguide.pdf see manual] for that.

= Install Software =
Add the modules from the kernel

== /etc/modules/ ==
Add these modules so they're loaded on boot. You can modprobe each one individually if you don't want to reboot.

<pre>i2c_dev
i2c_bcm2708
i2c:mcp7941x</pre>

== /media/mmcblk0p1/config.txt ==
You will need to mount this as read-write

{{cmd|mount -o remount,rw /media/mmcblk0p1}}

Add these two parameters to the bottom

<pre>dtparam=i2c1=on
dtparam=i2c_arm=on</pre>

{{cmd|mount -o remount,ro /media/mmcblk0p1}}

Then you will need to reboot.

== Binding the hardware clock device ==

You will want to make sure the device is created when hwclock starts, if it isn't already created. To the bottom of /etc/conf.d/hwclock add this:

<pre>start_pre() {
if [ -d "/sys/class/i2c-adapter/i2c-1/i2c-dev/i2c-1" ]; then
einfo "Creating RTC device";
echo mcp7941x 0x6f > /sys/class/i2c-adapter/i2c-1/new_device
fi
}</pre>

For the time being this is necessary but in the future when [https://github.com/raspberrypi/linux/issues/1032 issue 1032] you should be able to just add

<pre>dtparam=i2c-rtc,mcp7941x</pre>

to /media/mmcblk0p1/config.txt

== Starting hwclock on boot ==
The hwclock service needs to be started for the hardware clock device to actually do anything. Check if hwclock has been started by running this command:

{{cmd|rc-status {{!}} grep hwclock}}

If it outputs

<pre> hwclock [ started ]</pre>

hwclock has already started. Otherwise start it manually and add it to the default init.d runlevel, so that it starts at boot time:

{{cmd|sudo rc-service hwclock start}}
{{cmd|sudo rc-update add hwclock default}}

If you are running Alpine Linux in the diskless mode (non-persistent root filesystem), save the configuration by:

{{cmd|sudo lbu commit -d}}

[[Category:Hardware]]
[[Category:System Administration]]
[[Category:Raspberry]]

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Setup Hardware Clock (RTC) Module on a Raspberry Pi