PTPd

PTPd is an open source implementation of the Precision Time Protocol for Unix-like computers.
Accuracy.
PTPd accuracy depends on how IEEE 1588 packets are timestamped on the participating machines. When IEEE 1588 packets are timestamped in software, interrupt latency, OS scheduling, and other software issues reduce the accuracy of the acquired timestamps, and therefore, the accuracy of time synchronization. The presence of hardware-assisted timestamping makes it possible to acquire more precise send and receive timestamps. A test in 2010 on an Intel Gigabit network card noted offset converging to varying between around 1–100 microseconds in a pure software implementation, and to around a microsecond when using hardware-assisted PTP.