GG for Arduino is a serial console library. It also contains various functions for implementing the console, for example printf(). You can implement a command line interface on your Arduino and add ...

If I try to use Serial.printf to print two uint64_t variables, the 2nd one prints as a zero... Arduino 1.8.13 Feather M0 Adafruit SAMD21 Boards 1.6.0 ...

While the Arduino family of boards connect to your computer using a USB virtual serial port, the ATmega ones have an actual serial connection on-board.