The technical memorandum: A Kernel Programming Interface for Precision Time Signals (PostScript) describes a proposed programming interface for external precision time signals, such as the pulse-per-second (PPS) signal generated by some radio clocks and cesium oscillators.
The memorandum argues for a generic capability in the ubiquitous Unix kernel, which could be used for a wide variety of measurement applications, including network time synchronization and experiments involving performance measurement and evaluation of computer networks and transmission systems. The hardware to do this requires only a serial port and a modem control lead, such as the data carrier detect (DCD) lead, which can be driven by an external source via a level converter/pulse generator.