I've got a small Raspberry Pi clone set up with a GSP module running chronyd[2], advertised via DHCP as mentioned by GP. Didn't take much time or effort.
I also added a RTC module so it could hold reasonable time during power-loss but I haven't had a chance to verify that it works as expected.
[1]: https://www.aliexpress.com/item/1005001623104119.html The 7M and M8N are both much better than the 6M, regardless get a module with PPS output pin, not all have it. And grab an active antenna, you'll probably need it.
I did something similar but went a bit more overboard because I could partially write it off as an experiment for work. I found this carrier board for the CM4:
which is pretty nice because it has an onboard RTC and battery backup. I then added on a timing specific GPS module that was made to fit onto the GPIO pins (https://www.tindie.com/products/nsayer/gps-timing-module-bre...). The CM4 is interesting because it supports hardware timestamping on the ethernet so it can actually run PTP for ultra-precise synchronization. Also added one of those SPI 8 digit seven segment displays and wrote a crappy little program to update the time as fast as possible for some bling. It sucks the CM4 ended up being the biggest cost of the project since I ended up paying ~80 bucks for it. Still far cheaper than the cost of a "real" PTP host.
Sorry, yeah I mean Pi-like SBC, ie with GPIO. In my case a NanoPi NEO-LTS[1], mainly because I had one available and I didn't need much hardware just to run the NTP (it's all it does).
It runs Armbian[2] and has been sitting there doing its thing for a few years now.
All you need is a GPIO for PPS, but it's nice to have the UART so it can parse the time and such.
edit: since it's slightly different on Armbian from a Raspberry Pi, you need to enable the pps-gpio overlay similarly[3], but the pin parameter is different[4], for the H3 in the NanoPi NEO for example see here[5].
I also added a RTC module so it could hold reasonable time during power-loss but I haven't had a chance to verify that it works as expected.
[1]: https://www.aliexpress.com/item/1005001623104119.html The 7M and M8N are both much better than the 6M, regardless get a module with PPS output pin, not all have it. And grab an active antenna, you'll probably need it.
[2]: https://austinsnerdythings.com/2021/04/19/microsecond-accura...