19c2daa00SOllivier Robert<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"> 29c2daa00SOllivier Robert<html> 39c2daa00SOllivier Robert<head> 4ea906c41SOllivier Robert<meta http-equiv="content-type" content="text/html;charset=iso-8859-1"> 59c2daa00SOllivier Robert<meta name="generator" content="HTML Tidy, see www.w3.org"> 69c2daa00SOllivier Robert<title>Kernel Model for Precision Timekeeping</title> 79c2daa00SOllivier Robert<link href="scripts/style.css" type="text/css" rel="stylesheet"> 89c2daa00SOllivier Robert</head> 99c2daa00SOllivier Robert<body> 109c2daa00SOllivier Robert<h3>Kernel Model for Precision Timekeeping</h3> 119c2daa00SOllivier Robert<p><img src="pic/alice61.gif" alt="gif" align="left"> <a href="http://www.eecis.udel.edu/~mills/pictures.html">from <i>Pogo</i>, Walt Kelly</a></p> 12*2b15cb3dSCy Schubert<p>Alice finds the kernel a house of cards.</p> 13*2b15cb3dSCy Schubert<p>Last update: 14*2b15cb3dSCy Schubert <!-- #BeginDate format:En2m -->10-Mar-2014 05:10<!-- #EndDate --> 15*2b15cb3dSCy Schubert UTC</p> 169c2daa00SOllivier Robert<br clear="left"> 179c2daa00SOllivier Robert<h4>Related Links</h4> 18*2b15cb3dSCy Schubert<script type="text/javascript" language="javascript" src="scripts/misc.txt"></script> 199c2daa00SOllivier Robert<hr> 20*2b15cb3dSCy Schubert<p>The technical report [2], which is a revision and update of an earlier report [3], describes an engineering model for a precision clock discipline function for a generic operating system. The model is the same hybrid phase/frequecy-lock feedback loop used by <tt>ntpd</tt>, but implemented in the kernel. The code described in [2] is included in Solaris and Digital/Compaq/HP Tru64. It provides two system calls <tt>ntp_gettime()</tt> and <tt>ntp_adjtime()</tt> and can discipline the system clock with microsecond resolution. However, newer hardware and kernels with the same system calls can discipline the clock with nanosecond resolution. The new code described in [1] is in FreeBSD, Linux and Tru64. The software and documentation, including a simulator used to verify correct behavior, but not involving licensed code, is available in the <a href="ftp://ftp.udel.edu/pub/ntp/software/nanokernel.tar.gz">nanokernel.tar.gz</a> distribution</p> 21*2b15cb3dSCy Schubert<p>Ordinarily, the kernel clock discipline function is used with the NTP daemon, but could be used for other purposes. The <a href="ntptime.html"><tt>ntptime</tt></a> utility program can be used to control it manually.</p> 22*2b15cb3dSCy Schubert<p>The kernel model also provides support for an external precision timing source, such as described in the <a href="pps.html">Pulse-per-second (PPS) Signal Interfacing</a> page. The new system calls are used by the <a href="kernpps.html">PPSAPI interface</a> and in turn by the <a href="drivers/driver22.html">PPS Clock Discipline</a> driver (type 22) to provide synchronization limited in principle only by the accuracy and stability of the external timing source. Typical results with the PPS signal from a GPS receiver and a modern computer are in the 3 μs range.</p> 239c2daa00SOllivier Robert<h4>References</h4> 249c2daa00SOllivier Robert<ol> 25*2b15cb3dSCy Schubert <li>Mills, D.L., and P.-H. Kamp. The nanokernel. <i>Proc. Precision Time and Time Interval (PTTI) Applications and Planning Meeting</i> (Reston VA, November 2000). Paper: <a href="http://www.eecis.udel.edu/%7emills/database/papers/nano/nano2.ps">PostScript</a> | <a href="http://www.eecis.udel.edu/%7emills/database/papers/nano/nano2.pdf">PDF</a>, Slides: <a href="http://www.eecis.udel.edu/%7emills/database/brief/nano/nano.html">HTML</a> | <a href="http://www.eecis.udel.edu/%7emills/database/brief/nano/nano.ps">PostScript</a> | <a href="http://www.eecis.udel.edu/%7emills/database/brief/nano/nano.pdf">PDF</a> | <a href="http://www.eecis.udel.edu/%7emills/database/brief/nano/nano.ppt">PowerPoint</a></li> 26*2b15cb3dSCy Schubert <li>Mills, D.L. Unix kernel modifications for precision time synchronization. Electrical Engineering Department Report 94-10-1, University of Delaware, October 1994, 24 pp. Abstract: <a href="http://www.eecis.udel.edu/%7emills/database/reports/kern/kerna.ps">PostScript</a> | <a href="http://www.eecis.udel.edu/%7emills/database/reports/kern/kerna.pdf">PDF</a>, Body: <a href="http://www.eecis.udel.edu/%7emills/database/reports/kern/kernb.ps">PostScript</a> | <a href="http://www.eecis.udel.edu/%7emills/database/reports/kern/kernb.pdf">PDF</a></li> 27*2b15cb3dSCy Schubert <li>Mills, D.L. A kernel model for precision timekeeping. Network Working Group Report RFC-1589, University of Delaware, March 1994. 31 pp. <a href="http://www.eecis.udel.edu/%7emills/database/rfc/rfc1589.txt">ASCII</a></li> 289c2daa00SOllivier Robert</ol> 299c2daa00SOllivier Robert<hr> 309c2daa00SOllivier Robert<script type="text/javascript" language="javascript" src="scripts/footer.txt"></script> 319c2daa00SOllivier Robert</body> 329c2daa00SOllivier Robert</html> 33
