The SAMD21 microcontroller in the more recent Arduino board designs had a clock/calendar built-in. It’s one of the operating modes of the Real-Time Counter. There are counter fields fields for seconds, minutes, hours, (optional AM/PM), days, months, and years. However the year field is only 6 bits, allowing for only 64 years starting at a …
A friend of mine, David Sparks, is using a SAMD based board (a Seeedstudio XIAO) to be a real time clock. You can see his project here: https://github.com/IowaDave/SAMD21-RTC-Clock. The SAMD has a Real Time Counter which can be configured as a Real Time Clock (RTC=RTC!) eliminating the need for a second component. However when run …