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 | + | 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: | ||
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status = "okay"; | status = "okay"; | ||
| − | + | ds3231: ds3231@68 { | |
compatible = "maxim,ds3231"; | compatible = "maxim,ds3231"; | ||
reg = <0x68>; | reg = <0x68>; | ||
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</pre> | </pre> | ||
| + | == Accessing the rtc device == | ||
| + | Setting the RTC device as <code>rtc0</code> lets the system clock be synchronized. The related section can be added to the device tree as an ''alias'': | ||
| + | <pre class="board-terminal"> | ||
| + | aliases { | ||
| + | /* ds3231 is our default rtc dev (rtc0) */ | ||
| + | rtc0 = &ds3231; | ||
| + | rtc1 = &snvs_rtc; | ||
| + | }; | ||
| + | </pre> | ||
| − | + | The RTC device is available as <code>/dev/rtc0</code> device and the related time can be read using the <code>hwclock</code> command: | |
| − | The RTC device is available as <code>/dev/ | ||
<pre class="workstation-terminal"> | <pre class="workstation-terminal"> | ||
| − | root@desk-mx8mp:~# dmesg | grep | + | root@desk-mx8mp:~# dmesg | grep rtc0 |
| − | [ | + | [ 6.949783] rtc-ds1307 5-0068: registered as rtc0 |
| − | root@desk-mx8mp:~# hwclock -f /dev/ | + | root@desk-mx8mp:~# hwclock -f /dev/rtc0 |
2024-03-06 16:18:28.182912+01:00 | 2024-03-06 16:18:28.182912+01:00 | ||
root@desk-mx8mp:~# | root@desk-mx8mp:~# | ||
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</pre> | </pre> | ||
Latest revision as of 14:08, 18 April 2024
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 This application note has been validated using the kit version in the History table. |
Contents
HistoryEdit
| Version | Date | Development Kit version |
|---|---|---|
| 4.0.0 | Mar 2024 | DESK-MX8M-L 4.0.0 |
IntroductionEdit
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 driverEdit
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";
ds3231: ds3231@68 {
compatible = "maxim,ds3231";
reg = <0x68>;
status = "okay";
};
};
Accessing the rtc deviceEdit
Setting the RTC device as rtc0 lets the system clock be synchronized. The related section can be added to the device tree as an alias:
aliases {
/* ds3231 is our default rtc dev (rtc0) */
rtc0 = &ds3231;
rtc1 = &snvs_rtc;
};
The RTC device is available as /dev/rtc0 device and the related time can be read using the hwclock command:
root@desk-mx8mp:~# dmesg | grep rtc0 [ 6.949783] rtc-ds1307 5-0068: registered as rtc0 root@desk-mx8mp:~# hwclock -f /dev/rtc0 2024-03-06 16:18:28.182912+01:00 root@desk-mx8mp:~#
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:~#