Software-only implementations of slave clocks with sub-microsecond accuracy

Keeping slave clocks with sub-microsecond accuracy is believed to require hardware-assistance at physical layer and network. This paper presents software-only implementations of a slave for such accuracy. Time-stamps are read in the interrupt handler and a system resource conflicts detector filters out system-inside noise. We adopted Packet Inter-Arrival based clock servo technique that has fast convergence and high resistance to network queuing delay. The slave keeps time within one microsecond up to 80% of link utilization by cross traffic with dumb switching hubs. The precision of the software time-stamping is 17 ns and the synchronization accuracy is 76 ns.