Starting from firmware revision 112, ELLO 1A supports an optional real-time clock/calendar compatible with DS3231, connected on the I2C bus.
The easiest way to add an RTC to ELLO, would be by connecting one of the many available on the market DS3231 RTC modules. Some of those even match the needed pinout of the ELLO’s expansion connector. Only the four pins SCL, SDA, VCC, and GND are required for the connection.
The module in the picture is compatible with ELLO 1A and even includes an extra EEPROM chip on board. That additional memory could be accesses and used from within user’s programs through the use of the I2C functions in the <platform.h> library.
When recognised on power up, the presence of an RTC is indicated in the line of detected devices.
If the system lacks a RTC, it still counts time internally (although with somewhat lesser accuracy), but the date and time will always reset back to midnight on January 1, 2021 on every power off event.