DESK-RZ-L/Peripherals/Real Time Clock
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| Issue Date | Notes | ||
| 2025/12/16 | DESK-RZ-L-1.x.x release | ||
Contents
Peripheral RTC[edit | edit source]
There are 2 RTCs:
- Internal, integrated into the SoC
- External (on the SoM), at address
0x6Fon I2C B
Configuration[edit | edit source]
These peripheral(s) can only be used with the following ConfigID(s) (see the associated BOM):
| ConfigID | Note |
|---|---|
| 2002 | All RTCs are available |
| 2003 | The RTC on I2C B is not available (I2C B pins are used to drive motors) |
Device tree configuration[edit | edit source]
Below is an example of a device tree configuration used on a standard DAVE kit for the DSAB EVK.
From rzt2h-dsab.dtsi:
...
&rtc {
status = "okay";
};
...
&i2c1 {
...
rtc@6f {
compatible = "isil,isl1208";
reg = <0x6f>;
//external-oscillator;
};
};
...
Accessing the peripheral[edit | edit source]
Linux[edit | edit source]
... [ 2.848396] rtc rtc0: invalid alarm value: 1900-01-01T00:00:00 [ 2.854742] rzt2h-rtc 81009000.rtc: registered as rtc0 [ 2.859967] rzt2h-rtc 81009000.rtc: setting system clock to 2000-01-01T00:00:00 UTC (946684800) [ 2.902759] rtc-isl1208 1-006f: rtc power failure detected, please set clock. [ 2.910764] rtc-isl1208 1-006f: Using internal oscillator [ 2.917678] rtc-isl1208 1-006f: registered as rtc1 ...
RTC0[edit | edit source]
RTC integrated into the SoC, device /dev/rtc0, does not have backup power.
root@desk-t2h-usd-devel:~# hwclock -r -f /dev/rtc0 2000-01-01 00:17:22.068661+00:00 root@desk-t2h-usd-devel:~# date -s "2025-12-16 13:00:00" Tue Dec 16 13:00:00 UTC 2025 root@desk-t2h-usd-devel:~# hwclock -w -f /dev/rtc0 root@desk-t2h-usd-devel:~# hwclock -r -f /dev/rtc0 2025-12-16 13:00:07.248735+00:00 root@desk-t2h-usd-devel:~# sleep 10 root@desk-t2h-usd-devel:~# hwclock -r -f /dev/rtc0 2025-12-16 13:00:21.072782+00:00
RTC1[edit | edit source]
The external RTC is present on the SoM on I2C bus B and is not available in the carrier board configured as ConfigID 2003.
Backup power can be provided via the connector J5 or battery on J6:
The command hwclock -r -f /dev/rtc1 cannot be used; access must be done through the driver.
root@desk-t2h-usd-devel:~# hwclock --systohc -w -f /dev/rtc1 root@desk-t2h-usd-devel:~# cat /sys/class/rtc/rtc1/time 13:09:58 root@desk-t2h-usd-devel:~# sleep 10 root@desk-t2h-usd-devel:~# cat /sys/class/rtc/rtc1/time 13:10:11
