Only works on Linux.

1. Follow these instructions to flash your Arduino with client.ino using arduino-cli. Following these steps will also get you the name of the USB port used for serial communication.

2. Compile host.c with gcc -O2 host.c.

3. With Arduino still plugged in to the same port, run the program with:

   ./a.out {name_of_usb_port} {output_filename}

File {output_filename} will contain as accurate as possible timestamp measurements based on NTP with nanosecond resolution. The format of {output_filename} is:

{unix_timestamp_seconds} {nanoseconds}

Each line represents the timestamp after what is supposed to be 1 minute on the Arduino from the previous.

Measurements on the Arduino are based on exact clock ticks using overflow interrupts.