This post documents building a PTP (Precision Time Protocol) grandmaster using a Raspberry Pi CM4 and SR1723U10 GPS module. The author built a cost-effective alternative to the typical Time HAT solution, spending approximately $103 in new parts while leveraging existing CM4 and IO board hardware. Unlike the Time HAT approach requiring a high-end GPS module and extra electronics, this build targets those wanting to understand how PTP operates at the physical layer without production deployment costs.

The implementation relies on the CM4's BCM54210 PE Ethernet PHY, which provides hardware timestamping capabilities essential for achieving sub-microsecond synchronization across the homelab. Compared to alternatives involving Time HAT paths costing well over $475, this build offers a fraction of the expense while demonstrating core principles of IEEE 1588v2 distribution. The system runs on Ubuntu 24.04 with kernel 6.8.0-raspi, featuring proper hardware clock configuration via dtoverlay settings and disabled Bluetooth.

The entire setup integrates clients including a Turing Pi 2 cluster and RK1 compute modules into a unified RTL8370 MB-CG+ switch fabric, ensuring minimal latency between the grandmaster and endpoints.