Difference between revisions of "DESK-MX8M-AN-0003: Add an external RTC to SBC ORCA"
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== Linux driver == | == Linux driver == | ||
| − | [[DESK-MX8M-L/General/Release_Notes#DESK-MX8M-L_4.0.0|DESK-MX8M-L 4.0.0]] kernel has | + | [[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 and probe the kernel module. | It is enough to connect the RTC board to an I2C and probe the kernel module. | ||
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}; | }; | ||
</pre> | </pre> | ||
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== Accessing the rtc device == | == Accessing the rtc device == | ||
Revision as of 15:58, 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 script can be used for sysnchronizing the system clock from the hardware rtc device:
[Unit] Description=Synchronise System clock to hardware RTC DefaultDependencies=no After=systemd-modules-load.service Before=systemd-journald.service time-sync.target sysinit.target shutdown.target Conflicts=shutdown.target [Service] Type=oneshot RemainAfterExit=yes ExecStart=/etc/hwrtc.sh RestrictRealtime=yes [Install] WantedBy=sysinit.target
where the startup script is /etc/hwrtc.sh used for probing the rtc-ds1307 kernel module:
#!/bin/sh modprobe rtc-ds1307 sleep 1 hwclock -f /dev/rtc1 --hctosys exit 0
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:~#
