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diff --git a/contrib/ntp/html/refclock.htm b/contrib/ntp/html/refclock.htm index 80c62a265a59..4b2611d7e38e 100644 --- a/contrib/ntp/html/refclock.htm +++ b/contrib/ntp/html/refclock.htm @@ -1,157 +1,250 @@ -<html><head><title> -Reference Clock Drivers -</title></head><body><h3> -Reference Clock Drivers -</H3> +<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"> +<html> +<head> +<meta name="generator" content="HTML Tidy, see www.w3.org"> +<title>Reference Clock Drivers</title> +</head> +<body> +<h3>Reference Clock Drivers</h3> -<IMG ALIGN=LEFT SRC=pic/tardisa.gif>From top: +<img align="left" src="pic/stack1a.jpg" alt="gif">Master Time +Facility at the <a href="http://www.eecis.udel.edu/~mills/lab.htm"> +UDel Internet Research Laboratory</a>: <br clear="left"> +<hr> +<p>Support for most of the commonly available radio and modem +reference clocks is included in the default configuration of the +NTP daemon for Unix <tt>ntpd</tt>. Individual clocks can be +activated by configuration file commands, specifically the <tt> +server</tt> and <tt>fudge</tt> commands described in the <a href= +"ntpd.htm"><tt>ntpd</tt> program manual page</a>. The following +discussion presents Information on how to select and configure the +device drivers in a running Unix system.</p> + +<p>Many radio reference clocks can be set to display local time as +adjusted for timezone and daylight saving mode. For use with NTP +the clock must be set for Coordinated Universal Time (UTC) only. +Ordinarily, these adjustments are performed by the kernel, so the +fact that the clock runs on UTC will be transparent to the +user.</p> + +<p>Radio and modem clocks by convention have addresses in the form +127.127.<i>t.u</i>, where <i>t</i> is the clock type and <i>u</i> +is a unit number in the range 0-3 used to distinguish multiple +instances of clocks of the same type. Most of these clocks require +support in the form of a serial port or special bus peripheral, but +some can work directly from the audio codec found in some +workstations. The particular device is normally specified by adding +a soft link <tt>/dev/device<i>u</i></tt> to the particular hardware +device involved, where <i><tt>u</tt></i> correspond to the unit +number above.</p> + +<p>Most clock drivers communicate with the reference clock using a +serial port, usually at 9600 bps. There are several application +program interfaces (API) used in the various Unix and NT systems, +most of which can be detected at configuration time. Thus, it is +important that the NTP daemon and utilities be compiled on the +target system or clone. In some cases special features are +available, such as timestamping in the kernel or pulse-per-second +(PPS) interface. In most cases these features can be detected at +configuration time as well; however, the kernel may have to be +recompiled in order for them to work.</p> + +<p>The audio drivers are a special case. These include support for +the NIST time/frequency stations WWV and WWVH, the Canadian +time/frequency station CHU and generic IRIG signals. Currently, +support for the Solaris and SunOS audio API is included in the +distribution. It is left to the volunteer corps to extend this +support to other systems. Further information on hookup, debugging +and monitoring is given in the <a href="audio.htm">Audio +Drivers</a> page.</p> + +<p>The local clock driver is also a special case. A server +configured with this driver can operate as a primary server to +synchronize other clients when no other external synchronization +sources are available. If the server is connected directly or +indirectly to the public Internet, there is some danger that it can +adversely affect the operation of unrelated clients. Carefully read +the <a href="driver1.htm">Undisciplined Local Clock</a> page and +respect the stratum limit.</p> + +<p>The local clock driver also supports an external synchronization +source such as a high resolution counter disciplined by a GPS +receiver, for example. Further information is on the <a href= +"extern.htm">External Clock Discipline and the Local Clock +Driver</a> page.</p> + +<h4>Driver Calibration</h4> + +<p>Some drivers depending on longwave and shortwave radio services +need to know the radio propagation time from the transmitter to the +receiver, which can amount to some tens of milliseconds. This must +be calculated for each specific receiver location and requires the +geographic coordinates of both the transmitter and receiver. The +transmitter coordinates for various radio services are given in the +<a href="qth.htm">Stations, Frequencies and Geographic +Coordinates</a> page. Receiver coordinates can be obtained or +estimated from various sources. The actual calculations are beyond +the scope of this document.</p> -<UL> +<p>When more than one clock driver is supported, it is often the +case that each shows small systematic offset differences relative +to the rest. To reduce the effects of jitter when switching from +one driver to the another, it is useful to calibrate the drivers to +a common ensemble offset. The <tt>enable calibrate</tt> +configuration command in the <a href="miscopt.htm">Miscellaneous +Options</a> page is useful for this purpose. The calibration +function can also be enabled and disabled using the <tt>ntpdc</tt> +program utility.</p> -<LI>Austron 2100A GPS Receiver with LORAN-C assist</LI> -<LI>Austron 2000 LORAN-C Receiver></LI> -<LI>Spectracom 8170 WWVB Receiver</LI> -<LI>Hewlett Packard 5061A Cesium Beam Standard</LI> +<p>Most clock drivers use the <tt>time1</tt> value specified in the +<tt>fudge</tt> configuration command to provide the calibration +correction when this cannot be provided by the clock or interface. +When the calibration function is enabled, the <tt>time1</tt> value +is automatically adjusted to match the offset of the remote server +or local clock driver selected for synchronization. Ordinarily, the +NTP selection algorithm chooses the best from among all sources, +usually the best radio clock determined on the basis of stratum, +synchronization distance and jitter. The calibration function +adjusts the <tt>time1</tt> values for all clock drivers except this +source so that their indicated offsets tend to zero. If the +selected source is the kernel PPS discipline, the <tt>fudge +time1</tt> values for all clock drivers are adjusted.</p> -</UL> +<p>The adjustment function is an exponential average designed to +improve accuracy, so the function takes some time to converge. The +recommended procedure is to enable the function, let it run for an +hour or so, then edit the configuration file using the <tt> +time1</tt> values displayed by the <tt>ntpq</tt> utility and <tt> +clockvar</tt> command. Finally, disable the calibration function to +avoid possible future disruptions due to misbehaving clocks or +drivers.</p> + +<h4>Performance Enhancements</h4> + +<p>In general, performance can be improved, especially when more +than one clock driver is supported, to use the prefer peer function +described in the <a href="prefer.htm">Mitigation Rules and the <tt> +prefer</tt> Keyword</a> page. The prefer peer is ordinarily +designated the remote peer or local clock driver which provides the +best quality time. All other things equal, only the prefer peer +source is used to discipline the system clock and jitter-producing +"clockhopping" between sources is avoided. This is valuable when +more than one clock driver is present and especially valuable when +the PPS clock driver (type 22) is used. Support for PPS signals is +summarized in the <a href="pps.htm">Pulse-per-second (PPS) Signal +Interfacing</a> page.</p> + +<p>Where the highest performance is required, generally better than +one millisecond, additional hardware and/or software functions may +be required. Kernel modifications for precision time are described +in the <a href="kern.htm">A Kernel Model for Precision +Timekeeping</a> page. Special line discipline and streams modules +for use in capturing precision timestamps are described in the <a +href="ldisc.htm">Line Disciplines and Streams Drivers</a> page.</p> + +<h4>Comprehensive List of Clock Drivers</h4> + +<p>Following is a list showing the type and title of each driver +currently implemented. The compile-time identifier for each is +shown in parentheses. Click on a selected type for specific +description and configuration documentation, including the clock +address, reference ID, driver ID, device name and serial line +speed, and features (line disciplines, etc.). For those drivers +without specific documentation, please contact the author listed in +the <a href="copyright.htm">Copyright Notice</a> page.</p> + +<p><a href="driver1.htm">Type 1</a> Undisciplined Local Clock +(<tt>LOCAL</tt>)<br> +<a href="driver2.htm">Type 2</a> Trak 8820 GPS Receiver +(<tt>GPS_TRAK</tt>)<br> +<a href="driver3.htm">Type 3</a> PSTI/Traconex 1020 WWV/WWVH +Receiver (<tt>WWV_PST</tt>)<br> +<a href="driver4.htm">Type 4</a> Spectracom WWVB and GPS Receivers +(<tt>WWVB_SPEC</tt>)<br> +<a href="driver5.htm">Type 5</a> TrueTime GPS/GOES/OMEGA Receivers +(<tt>TRUETIME</tt>)<br> +<a href="driver6.htm">Type 6</a> IRIG Audio Decoder +(<tt>IRIG_AUDIO</tt>)<br> +<a href="driver7.htm">Type 7</a> Radio CHU Audio +Demodulator/Decoder (<tt>CHU</tt>)<br> +<a href="driver8.htm">Type 8</a> Generic Reference Driver +(<tt>PARSE</tt>)<br> +<a href="driver9.htm">Type 9</a> Magnavox MX4200 GPS Receiver +(<tt>GPS_MX4200</tt>)<br> +<a href="driver10.htm">Type 10</a> Austron 2200A/2201A GPS +Receivers (<tt>GPS_AS2201</tt>)<br> +<a href="driver11.htm">Type 11</a> Arbiter 1088A/B GPS Receiver +(<tt>GPS_ARBITER</tt>)<br> +<a href="driver12.htm">Type 12</a> KSI/Odetics TPRO/S IRIG +Interface (<tt>IRIG_TPRO</tt>)<br> +Type 13 Leitch CSD 5300 Master Clock Controller +(<tt>ATOM_LEITCH</tt>)<br> +Type 14 EES M201 MSF Receiver (<tt>MSF_EES</tt>)<br> +<a href="driver5.htm">Type 15</a> * TrueTime generic receivers<br> +<a href="driver16">Type 16</a> Bancomm GPS/IRIG Receiver +(<tt>GPS_BANCOMM</tt>)<br> +Type 17 Datum Precision Time System (<tt>GPS_DATUM</tt>)<br> +<a href="driver18.htm">Type 18</a> NIST Modem Time Service +(<tt>ACTS_NIST</tt>)<br> +<a href="driver19.htm">Type 19</a> Heath WWV/WWVH Receiver +(<tt>WWV_HEATH</tt>)<br> +<a href="driver20.htm">Type 20</a> Generic NMEA GPS Receiver +(<tt>NMEA</tt>)<br> +Type 21 TrueTime GPS-VME Interface (<tt>GPS_VME</tt>)<br> +<a href="driver22.htm">Type 22</a> PPS Clock Discipline +(<tt>PPS</tt>)<br> +<a href="driver23.htm">Type 23</a> PTB Modem Time Service +(<tt>ACTS_PTB</tt>)<br> +<a href="driver24.htm">Type 24</a> USNO Modem Time Service +(<tt>ACTS_USNO</tt>)<br> +<a href="driver5.htm">Type 25</a> * TrueTime generic receivers<br> +<a href="driver26.htm">Type 26</a> Hewlett Packard 58503A GPS +Receiver (<tt>GPS_HP</tt>)<br> +<a href="driver27.htm">Type 27</a> Arcron MSF Receiver +(<tt>MSF_ARCRON</tt>)<br> +<a href="driver28.htm">Type 28</a> Shared Memory Driver +(<tt>SHM</tt>)<br> +<a href="driver29.htm">Type 29</a> Trimble Navigation Palisade GPS +(<tt>GPS_PALISADE</tt>)<br> +<a href="driver30.htm">Type 30</a> Motorola UT Oncore GPS +(<tt>GPS_ONCORE</tt>)<br> +Type 31 Rockwell Jupiter GPS (<tt>GPS_JUPITER</tt>)<br> +<a href="driver32.htm">Type 32</a> Chrono-log K-series WWVB +receiver <a href="driver33.htm">Type 33</a> Dumb Clock <a href= +"driver34.htm">Type 34</a> Ultralink WWVB Receivers<br> +<a href="driver35.htm">Type 35</a> Conrad Parallel Port Radio Clock +(<tt>PCF</tt>)<br> +<a href="driver36.htm">Type 36</a> Radio WWV/H Audio +Demodulator/Decoder(<tt>WWV</tt>)<br> +<a href="driver37.htm">Type 37</a> Forum Graphic GPS Dating station +(<tt>FG</tt>)<br> +<a href="driver38.htm">Type 38</a> hopf GPS/DCF77 6021/komp for +Serial Line (<tt>HOPF_S</tt>)<br> +<a href="driver39.htm">Type 39</a> hopf GPS/DCF77 6039 for PCI-Bus +(<tt>HOPF_P</tt>)</p> + +<p>* All TrueTime receivers are now supported by one driver, type +5. Types 15 and 25 will be retained only for a limited time and may +be reassigned in future.</p> + +<p>Additional Information</p> + +<p><a href="prefer.htm">Mitigation Rules and the <tt>prefer</tt> +Keyword</a><br> +<a href="rdebug.htm">Debugging Hints for Reference Clock +Drivers</a><br> +<a href="kern.htm">A Kernel Model for Precision Timekeeping</a><br> +<a href="ldisc.htm">Line Disciplines and Streams Drivers</a><br> +<a href="audio.htm">Reference Clock Audio Drivers</a><br> +<a href="pps.htm">Pulse-per-second (PPS) Signal Interfacing</a><br> +<a href="howto.htm">How To Write a Reference Clock Driver</a></p> -<br clear=left> -The Tardis <hr> +<a href="index.htm"><img align="left" src="pic/home.gif" alt= +"gif"></a> -Support for most of the commonly available radio and modem reference -clocks is included in the default configuration of the NTP daemon for -Unix <TT>ntpd</TT>. Individual clocks can be activated by configuration -file commands, specifically the <TT>server</TT> and <TT>fudge</TT> -commands described in the <A HREF=ntpd.htm><TT>ntpd</TT> program manual -page</A>. The following discussion presents Information on how to select -and configure the device drivers in a running Unix system. - -<P>Radio and modem clocks by convention have addresses in the form -127.127.<I>t.u</I>, where <I>t</I> is the clock type and <I>u</I> is a -unit number in the range 0-3 used to distinguish multiple instances of -clocks of the same type. Most of these clocks require support in the -form of a serial port or special bus peripheral, but some can work -directly from the audio codec found in some workstations. The particular -device is normally specified by adding a soft link -<TT>/dev/device<I>u</I></TT> to the particular hardware device involved, -where <I><TT>u</TT></I> correspond to the unit number above. +<address><a href="mailto:mills@udel.edu">David L. Mills +<mills@udel.edu></a></address> +</body> +</html> -<p>Most clock drivers communicate with the reference clock using a -serial port, usually at 9600 bps. There are several application program -interfaces (API) used in the various Unix and NT systems, most of which -can be detected at configuration time. Thus, it is important that the -NTP daemon and utilities be compiled on the target system or clone. In -some cases special features are available, such as timestamping in the -kernel or pulse-per-second (PPS) interface. In most cases these features -can be detected at configuration time as well; however, the kernel may -have to be recompiled in order for them to work. - -<p>The audio drivers are a special case. These include support for the -NIST time/frequency stations WWV and WWVH, the Canadian time/frequency -station CHU and generic IRIG signals. Currently, support for the Solaris -and SunOS audio API is included in the distribution. It is left to the -volunteer corps to extend this support to other systems. Further -information on hookup, debugging and monitoring is given in the <a -href=audio.htm>Audio Drivers</a> page. - -<p>Some drivers depending on longwave and shortwave radio services need -to know the radio propagation time from the transmitter to the receiver, -which can amount to some tens of milliseconds. This must be calculated -for each specific receiver location and requires the geographic -coordinates of both the transmitter and receiver. The transmitter -coordinates for various radio services are given in the <a -href=qth.htm>Stations, Frequencies and Geographic Coordinates</a> page. -Receiver coordinates can be obtained or estimated from various sources. -The actual calculations are beyond the scope of this document. - -<P>Following is a list showing the type and title of each driver -currently implemented. The compile-time identifier for each is shown in -parentheses. Click on a selected type for specific description and -configuration documentation, including the clock address, reference ID, -driver ID, device name and serial line speed, and features (line -disciplines, etc.). For those drivers without specific documentation, -please contact the author listed in the <A HREF=copyright.htm>Copyright -Notice</A> page. - -<P><A HREF=driver1.htm>Type 1</A> Undisciplined Local Clock -(<TT>LOCAL</TT>) -<BR><A HREF=driver2.htm>Type 2</A> Trak 8820 GPS Receiver -(<TT>GPS_TRAK</TT>) -<BR><A HREF=driver3.htm>Type 3</A> PSTI/Traconex 1020 WWV/WWVH -Receiver -(<TT>WWV_PST</TT>) -<BR><A HREF=driver4.htm>Type 4</A> Spectracom WWVB and GPS Receivers -(<TT>WWVB_SPEC</TT>) -<BR><A HREF=driver5.htm>Type 5</A> TrueTime GPS/GOES/OMEGA Receivers -(<TT>TRUETIME</TT>) -<BR><A HREF=driver6.htm>Type 6</A> IRIG Audio Decoder -(<TT>IRIG_AUDIO</TT>) -<BR><A HREF=driver7.htm>Type 7</A> Radio CHU Audio Demodulator/Decoder -(<TT>CHU</TT>) -<BR><A HREF=driver8.htm>Type 8</A> Generic Reference Driver -(<TT>PARSE</TT>) -<BR><A HREF=driver9.htm>Type 9</A> Magnavox MX4200 GPS Receiver -(<TT>GPS_MX4200</TT>) -<BR><A HREF=driver10.htm>Type 10</A> Austron 2200A/2201A GPS Receivers -(<TT>GPS_AS2201</TT>) -<BR><A HREF=driver11.htm>Type 11</A> Arbiter 1088A/B GPS Receiver -(<TT>GPS_ARBITER</TT>) -<BR><A HREF=driver12.htm>Type 12</A> KSI/Odetics TPRO/S IRIG Interface -(<TT>IRIG_TPRO</TT>) -<BR>Type 13 Leitch CSD 5300 Master Clock Controller -(<TT>ATOM_LEITCH</TT>) -<BR>Type 14 EES M201 MSF Receiver (<TT>MSF_EES</TT>) -<BR><A HREF=driver5.htm>Type 15</A> * TrueTime generic receivers -<BR>Type 16 Bancomm GPS/IRIG Receiver (<TT>GPS_BANCOMM</TT>) -<BR>Type 17 Datum Precision Time System (<TT>GPS_DATUM</TT>) -<BR><A HREF=driver18.htm>Type 18</A> NIST Modem Time Service -(<TT>ACTS_NIST</TT>) -<BR><A HREF=driver19.htm>Type 19</A> Heath WWV/WWVH Receiver -(<TT>WWV_HEATH</TT>) -<BR><A HREF=driver20.htm>Type 20</A> Generic NMEA GPS Receiver -(<TT>NMEA</TT>) -<BR>Type 21 TrueTime GPS-VME Interface (<TT>GPS_VME</TT>) -<BR><A HREF=driver22.htm>Type 22</A> PPS Clock Discipline -(<TT>PPS</TT>) -<BR><A HREF=driver23.htm>Type 23</A> PTB Modem Time Service -(<TT>ACTS_PTB</TT>) -<BR><A HREF=driver24.htm>Type 24</A> USNO Modem Time Service -(<TT>ACTS_USNO</TT>) -<BR><A HREF=driver5.htm>Type 25</A> * TrueTime generic receivers -<BR><A HREF=driver26.htm>Type 26</A> Hewlett Packard 58503A GPS -Receiver (<TT>GPS_HP</TT>) -<BR><A HREF=driver27.htm>Type 27</A> Arcron MSF Receiver -(<TT>MSF_ARCRON</TT>) -<BR><A HREF=driver28.htm>Type 28</A> Shared Memory Driver -(<TT>SHM</TT>) -<BR><A HREF=driver29.htm>Type 29</A> Trimble Navigation Palisade GPS -(<TT>GPS_PALISADE</TT>) -<BR><A HREF=driver30.htm>Type 30</A> Motorola UT Oncore GPS -(<TT>GPS_ONCORE</TT>) -<BR>Type 31 Rockwell Jupiter GPS (<TT>GPS_JUPITER</TT>) -<BR><A HREF=driver34.htm>Type 34</A> Ultralink WWVB Receivers -<BR><A HREF=driver35.htm>Type 35</A> Conrad Parallel Port Radio Clock -(<TT>PCF</TT>) -<BR><A HREF=driver36.htm>Type 36</A> Radio WWV/H Audio -Demodulator/Decoder(<TT>WWV</TT>) -<BR><A HREF=driver37.htm>Type 37</A> Forum Graphic GPS Dating station -(<TT>FG</TT>) - -<P>* All TrueTime receivers are now supported by one driver, type 5. -Types 15 and 25 will be retained only for a limited time and may be -reassigned in future. -<P>Additional Information -<P><A HREF=prefer.htm>Mitigation Rules and the <TT>prefer</TT> -Keyword</A> -<BR><A HREF=rdebug.htm>Debugging Hints for Reference Clock Drivers</A> -<BR><A HREF=ldisc.htm>Line Disciplines and Streams Drivers</A> -<BR><A HREF=audio.htm>Reference Clock Audio Drivers</A> -<BR><A HREF=pps.htm>Pulse-per-second (PPS) Signal Interfacing</A> -<BR><A HREF=howto.htm>How To Write a Reference Clock Driver</A> -<BR><A HREF=index.htm>The Network Time Protocol (NTP) -Distribution </A> - -<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> |