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RTC Interface

The Radxa CM4 IO Board comes with an onboard RTC (Real-Time Clock) interface for connecting a button cell battery.

Hardware Connection​

Install a CR1220 button cell battery into the RTC interface of the Radxa CM4 IO Board. Pay attention to the battery polarity during installation - the positive and negative poles are clearly marked on the board's silkscreen.

Interface Location

You can refer to the Hardware Information tutorial to locate the corresponding hardware interface.

RTC Configuration​

Verify RTC Hardware​

Use the following command to verify if the RTC hardware is functioning properly.

radxa@device$
sudo dmesg | grep rtc

If the output includes a line containing rtc information is valid, it indicates that the RTC battery has been correctly recognized.

[    8.145303] [drm] Esmart1-win0(possible_vp_mask = 0x00000006) has no possible crtcs
[    8.145370] [drm] Esmart3-win0(possible_vp_mask = 0x00000006) has no possible crtcs
[    8.153133] rockchip-drm display-subsystem: [drm] Cannot find any crtc or sizes
[    8.154487] rockchip-drm display-subsystem: [drm] Cannot find any crtc or sizes
[    8.700833] rtc-hym8563 2-0051: hym8563_init_device: error read i2c data -6
[    8.716545] rtc-hym8563 2-0051: rtc information is valid
[    8.724597] rtc-hym8563 2-0051: registered as rtc0
[    8.725670] rtc-hym8563 2-0051: setting system clock to 2000-01-01T00:00:23 UTC (946684823)

Read RTC Time​

Use the hwclock command to read the current time from the RTC chip (/dev/rtc0).

radxa@device$
sudo hwclock -r -f /dev/rtc0

Display System Time​

Use the date command to display the current system time.

radxa@device$
date

Set RTC Time​

If the RTC time is not synchronized with the system time, you can write the current system time to the RTC using the hwclock command.

radxa@device$
sudo hwclock -w -f /dev/rtc0

Verify RTC Functionality​

  1. Note down the current system time
  2. Disconnect the board's power and network connections
  3. Wait for approximately 10 minutes
  4. Reconnect the power
  5. Observe if the system time continues to count correctly

Interface Pin Definitions​

For detailed pin definitions, please refer to the hardware schematics available on the Downloads page.