Raspberry-Pi

While investigating a separate network issue at work, we observed unexpected Ethernet link behavior on an embedded ARM system. During boot, the switch port facing it reports link up at 100 Mbps, then down, then up at 100 Mbps again, three times in total, before finally settling at 1 Gbps once the operating system is up. Before proceeding, we needed to determine whether the cycling was related to the issue at hand or independent behavior that could be ruled out. ...

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. ...