<html><head><title> Kernel Programming Interface for Precision Time Signals Network Performance Evaluation </title></head><body><h3> Kernel Programming Interface for Precision Time Signals </h3><hr> <p>The technical report [1] describes a proposed application programming interface (API) for external precision time signals, such as the pulse-per-second (PPS) signal generated by some radio clocks and cesium oscillators. The report 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. <p>Support for this API has been implemented in the NTP Version 4 software distribution. The <tt>/usr/include/sys/timepps.h</tt> header file defines the API interface routines and data structures. The API obsoletes previous APIs based on the <tt>tty_clock</tt> and <tt>ppsclock</tt> line disciplines and streams modules, which are no longer supported. The API used by the <a href=driver22.htm>PPS Clock Discipline</a> driver (type 22) to support PPS signals via either a serial port or parallel port, depending on the operating system. The API is supported in stock FreeBSD from 3.4 and with the addition of the <tt>PPSkit</tt> kernel software in Linux. Limited support for Solaris from 2.8 is available using the <tt>timepps.h.solaris</tt> header file included in this distribution. Copy this file to <tt>/usr/include/sys</tt> before configuring the distributution. <p>The API is normally used in conjunction with the precision time kernel modifications described in the <a href=kern.htm>Kernel Model for Precision Timekeeping</a> page. <h4>Reference</h4> <ol> <p><li>Mogul, J., D. Mills, J. Brittenson, J. Stone and U. Windl. Pulse-per-second API for Unix-like operating systems, version 1. Request for Comments RFC-2783, Internet Engineering Task Force, March 2000, 31 pp. <a href=http://www.eecis.udel.edu/~mills/database/rfc/rfc2783.txt>ASCII</a> </ol> <hr><a href=index.htm><img align=left src=pic/home.gif></a><address><a href=mailto:mills@udel.edu> David L. Mills <mills@udel.edu></a> </address></a></body></html>