A Realtime Clock (RTC) is an important functionality in an embedded system to keep the time accurate even when the device is not powered. Unlike the C1+ and the C0, the Odroid-C2 and C4 do not have an RTC circuitry on board.
An external RTC board like this PCF8563 RTC Shield is a good addition to your Odroid-C2/C4. This board uses I2C interface and plugs directly to the Odroid-C2/C4 GPIO pin (refer picture). The shield runs on a common CR2032 coin cell which can keep it running for about 2 years. This battery is replaceable and included with the purchase.
This shield fits nicely in the Odroid official case.
For the time being, this RTC Shield does not work on Odroid-C4 running on Android, pending for Android drivers update.
