The SAMD21 has an RTC peripheral that can be clocked from an external 32768 Hz crystal (or from the internal 32 K). Some board even have this crystal connected so it's just programming at that point
The SAMD21 has an RTC peripheral that can be clocked from an external 32768 Hz crystal (or from the internal 32 K). Some board even have this crystal connected so it's just programming at that point