[time-nuts] Ryzen mobos with serial port for Garmin GPS?

[Rich Wales]

Looking to design my next Linux (Ubuntu) system, built around a Ryzen 
processor.

In previous systems, I've had great success using a Garmin GPS 18x unit 
(small hockey puck with a wire tail) hooked up to a DB9 serial (COM) 
port on the motherboard, to provide a local (stratum-0) time reference 
via gpsd and chronyd.  However, mobos with a serial port are becoming 
harder to find.

(Yes, I know that PCI serial port cards exist -- however, these are not 
suitable for connecting a GPS time reference because the PPS signal 
timing is unpredictable -- so I've limited myself to using motherboards 
with a builtin serial port.)

What Ryzen (Socket AM4) motherboards have worked out well for people who 
want to do what I'm proposing?

Alternatively, can anyone recommend a better hardware solution than a 
Garmin GPS attached via a serial port?

Thanks for any suggestions.

*Rich Wales*
richw at richw.org