Difference between revisions of "DESK-MX8M-AN-0003: Add an external RTC to SBC ORCA"
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</pre> | </pre> | ||
| − | A proper ''systemd'' | + | A proper ''systemd'' service <code>/lib/systemd/system/hwrtc.service</code> can be used for synchronizing the system clock from the hardware rtc device: |
<pre> | <pre> | ||
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WantedBy=multi-user.target | WantedBy=multi-user.target | ||
</pre> | </pre> | ||
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| + | and the service has to be enabled: | ||
| + | |||
| + | systemctl enable hwrtc.service | ||
Now the <code>date</code> command shows the system clock synchronized at any reboot. | Now the <code>date</code> command shows the system clock synchronized at any reboot. | ||
Revision as of 16:38, 6 March 2024
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 This application note has been validated using the kit version in the History table. |
History[edit | edit source]
| Version | Date | Development Kit version |
|---|---|---|
| 4.0.0 | Mar 2024 | DESK-MX8M-L 4.0.0 |
Introduction[edit | edit source]
An external RTC device can be connected to ORCA SBC to keep date & time and synchronizing the system clock at boot time.
As an example, an easy - just ready - RTC small board can be bought from Amazon with the DS3231 RTC device.
Linux driver[edit | edit source]
DESK-MX8M-L 4.0.0 kernel has the related rtc-ds1307 driver module already built and available in the root file system image.
It is enough to connect the RTC board to an I2C and probe the kernel module.
For the purposes of this AN, it is possible to use the GROOVE connector which has the four required signals available: SCL, SDA, VDD, GND (see the SBC schematics page).
Then, the driver has to be enabled in the device tree using the i2c6 interface available in the GROOVE connector:
/* groove connector */
&i2c6 {
clock-frequency = <100000>;
pinctrl-names = "default";
pinctrl-0 = <&pinctrl_i2c6>;
status = "okay";
rtc: ds3231@68 {
compatible = "maxim,ds3231";
reg = <0x68>;
status = "okay";
};
};
Accessing the rtc device[edit | edit source]
The RTC device is available as /dev/rtc1 device and the related time can be read using the hwclock command:
root@desk-mx8mp:~# dmesg | grep rtc1 [ 5.794607] rtc-ds1307 5-0068: registered as rtc1 root@desk-mx8mp:~# hwclock -f /dev/rtc1 2024-03-06 16:18:28.182912+01:00 root@desk-mx8mp:~#
A proper systemd service /lib/systemd/system/hwrtc.service can be used for synchronizing the system clock from the hardware rtc device:
[Unit] Description=Synchronise System clock to hardware RTC DefaultDependencies=no After=ntpdate.service Conflicts=shutdown.target [Service] Type=oneshot RemainAfterExit=yes ExecStart=/sbin/hwclock -f /dev/rtc1 --hctosys RestrictRealtime=yes [Install] WantedBy=multi-user.target
and the service has to be enabled:
systemctl enable hwrtc.service
Now the date command shows the system clock synchronized at any reboot.
root@desk-mx8mp:~# date Wed Mar 6 16:40:44 CET 2024 root@desk-mx8mp:~#
