rpi3 clock drift

[Stefan Parvu]

> I was thinking of ordering an I2C RTC but I'm unsure how to make FreeBSD aware of the clock.

We are currently using and heavily testing this RTC: 
https://afterthoughtsoftware.com/products/rasclock 

based on NXP PCF2129. See here complete description of a product based on FreeBSD 12 and RPI3+
https://kronometrix.com/wp-content/uploads/2019/11/Kronometrix-K1.pdf 

Follow this thread for more instructions and hints how to get this RTC working with FreeBSD 12.
http://freebsd.1045724.x6.nabble.com/Rasclock-PCF2127-Hardware-Clock-FreeBSD-12-0-td6339218.html 

Stefan