Difference between revisions of "DESK-MX8M-AN-0003: Add an external RTC to SBC ORCA"
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[[DESK-MX8M-L/General/Release_Notes#DESK-MX8M-L_4.0.0|DESK-MX8M-L 4.0.0]] kernel has the related <code>rtc-ds1307</code> driver module already built and available in the root file system image. | [[DESK-MX8M-L/General/Release_Notes#DESK-MX8M-L_4.0.0|DESK-MX8M-L 4.0.0]] kernel has the related <code>rtc-ds1307</code> driver module already built and available in the root file system image. | ||
| − | It is enough to connect the RTC board to an I2C | + | It is enough to connect the RTC board to an I2C: 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 [[ORCA_SOM/ORCA_Evaluation_Kit/Electrical_and_Mechanical_Documents/Schematics | schematics]] page). |
| − | |||
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Then, the driver has to be enabled in the device tree using the <code>i2c6</code> interface available in the GROOVE connector: | Then, the driver has to be enabled in the device tree using the <code>i2c6</code> interface available in the GROOVE connector: | ||
Revision as of 16:39, 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: 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:~#
