I wanted to measure how much latency a network device adds to a path, precisely enough to characterize a DUT (Device Under Test) that adds less than a microsecond. The instrument is a quad-port Intel i350, which does per-packet hardware timestamping and exposes a PTP hardware clock per port. The DUTs: a Netgear FE104 repeater hub, a Netgear FS105 10/100 switch, and a Netgear GS305 gigabit switch. Results up front: ...
This is part 2 of the homelab PTP grandmaster series. Part 1 used a Raspberry Pi CM4 with SatPulse. This build uses a NanoPi R5S-LTS and takes a different path to the same destination. The R5S has no standard GPIO header. It has an FPC connector. Getting a GPS module talking to it required a breakout board, a ribbon cable, a soldering iron, and more debugging than expected. The results made it worth it. ...
I work with industrial infrastructure that requires nanosecond-accurate time synchronization. The commercial GPS-disciplined PTP grandmaster clocks that solve this problem run from several thousand dollars on the low end, and considerably more with options and support. I had CM4s and CM4 IO boards already sitting in the lab. A TimeHAT with an OCP M.2 GNSS module would have been the cleaner path at around $400, but that is steep when the goal is learning how PTP actually works, not deploying production infrastructure. This build came in at around $103 in new parts. ...