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diff --git a/contrib/ntp/html/pps.htm b/contrib/ntp/html/pps.htm deleted file mode 100644 index a20dd4d..0000000 --- a/contrib/ntp/html/pps.htm +++ /dev/null @@ -1,106 +0,0 @@ -<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"> -<html> -<head> -<meta name="generator" content="HTML Tidy, see www.w3.org"> -<title>Pulse-per-second (PPS) Signal Interfacing</title> -</head> -<body> -<h3>Pulse-per-second (PPS) Signal Interfacing</h3> - -<img align="left" src="pic/alice32.gif" alt="gif"><a href= -"http://www.eecis.udel.edu/~mills/pictures.htm">from <i>Alice's -Adventures in Wonderland</i>, Lewis Carroll</a> - -<p>Alice is trying to find the PPS signal connector.<br clear= -"left"> -</p> - -<hr> -<p>Some radio clocks and related timekeeping gear have a -pulse-per-second (PPS) signal that can be used to discipline the -local clock oscillator to a high degree of precision, typically to -the order less than 10 <font face="Symbol">m</font>s in time and -0.01 parts-per-million (PPM) in frequency. The PPS signal can be -connected in either of two ways: via the data carrier detector -(DCD) pin of a serial port or via the acknowledge (ACK) pin of a -parallel port, depending on the hardware and operating system. -Connection via a serial port may require signal conversion and -regeneration to RS232 levels, which can be done using a circuit -such as described in the <a href="gadget.htm">Gadget Box PPS Level -Converter and CHU Modem</a> page. Note that NTP no longer supports -connection via the data leads of a serial port.</p> - -<p>Both the serial and parallel port connection require operating -system support, which is available in only a few operating systems, -including Linux, FreeBSD and latest Solaris beginning with 2.7. -Support on an experimental basis is available for several older -systems, including SunOS, Digital Ultrix and HP-UX, and in current -Digital Tru64 (Alpha). The PPS application program interface -defined in RFC-2783 (PPSAPI) is the only interface currently -supported. Older PPS interfaces based on the <tt>ppsclock</tt> and -<tt>tty_clk</tt> streams modules are no longer supported. As the -PPSAPI is expected to become an IETF cross-platform standard, it -should be used by new applications.</p> - -<p>The PPSAPI inerface requires a <tt> -/usr/include/sys/ppstime.h</tt> header file. This file is included -in Linux and FreeBSD distributions, but not in other distributions -or standard workstation products at this time. Header files for -other systems, including Solaris, can be found in the <tt> -nanokernel.tar.gz</tt> distribution, which can be found via the -Collaboration Resources link at www.ntp.org. The top level -directory contains a number of subdirectories for each -architecture, including Solaris. The <tt>ppstime.h</tt> file for -each architecture can be found in the subdirectory of the same -name.</p> - -<p>In the preferred mode of operation, PPS signals are processed by -the <a href="driver22.htm">PPS Clock Discipline</a> driver and -other clock drivers which might be involved need not know or care -about them. In some cases where there is no other driver, time -might be obtained from remote NTP servers via the network and local -PPS signals, for instance from a calibrated cesium oscillator, used -to stabilize the frequency and remove network jitter. Note that the -<tt>pps</tt> configuration command has been obsoleted by this -driver.</p> - -<p>The PPS driver operates in conjunction with a preferred peer, as -described in the <a href="prefer.htm">Mitigation Rules and the <tt> -prefer</tt> Keyword</a> page. One of the drivers described in the -<a href="refclock.htm">Reference Clock Drivers</a> page or another -NTP server furnishes the coarse timing and disambiguates the -seconds numbering of the PPS signal itself. The NTP daemon -mitigates between the clock driver or NTP server and the PPS driver -as described in that page in order to provide the most accurate -time, while respecting the various types of equipment failures that -could happen.</p> - -<p>Some Unix system kernels support a PPS signal directly, as -described in the <a href="kern.htm">A Kernel Model for Precision -Timekeeping</a> page. Specifically, the PPS driver can be used to -direct the PPS signal to the kernel for use as a discipline source -for both time and frequency. The presence of the kernel support is -automatically detected during the NTP build process and supporting -code automatically compiled. Note that the PPS driver does not -normally enable the PPS kernel code, since performance is generally -better without it. However, this code can be enabled by a driver -fudge flag if necessary.</p> - -<p>Some configurations may include multiple radio clocks with -individual PPS outputs. In some PPSAPI designs multiple PPS signals -can be connected to multiple instances of the PPS driver. In such -cases the NTP mitigation and grooming algorithms operate with all -the radio timecodes and PPS signals to develop the highest degree -of redundancy and survivability.</p> - -<hr> -<a href="index.htm"><img align="left" src="pic/home.gif" alt= -"gif"></a><br> -<br> - - -<address><a href="mailto:mills@udel.edu">David L. Mills -<mills@udel.edu></a></address> -</body> -</html> - |
