Using the Real Time Clock (RTC) on Zymkey

Zymkey would be able to provide a stable time reference when your host computer boots up. From that point on, you can reference the time using the standard libraries (e.g. time function call in C or date command line utility). However, the host pi clock will continue to drift independently after the boot-time reference is obtained from Zymkey. Another option would be to call the Zymkey API to get the clock in C/C++/Python.

We don’t expose an API which would allow one to set the Zymkey RTC since Zymkey is considered to be a secure device. Instead, an interface daemon determines when NTP is synchronized and enabled and sets the time from the current system time.

Hope this helps.

Thanks for your answer.
So if I do not have any NTP, I cannot set the time or adjust it if needed ? My device will never be connected to any ntp server…

This is true. We think of the Zymkey’s RTC as more of a “time bootstrap” during power and/or network outages. And, to promote security, we don’t allow the time to be set in user space by an arbitrary application. Although I don’t know the exact circumstances in your use case, in a real deployment which would never be in contact with an NTP time source, I would recommend allowing the time to be set by NTP one time before deployment in the field.