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diff --git a/contrib/ntp/html/driver22.htm b/contrib/ntp/html/driver22.htm new file mode 100644 index 0000000..313d2b8 --- /dev/null +++ b/contrib/ntp/html/driver22.htm @@ -0,0 +1,129 @@ +<HTML> +<HEAD> + <META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1"> + <META NAME="GENERATOR" CONTENT="Mozilla/4.01 [en] (Win95; I) [Netscape]"> + <TITLE>PPS Clock Discipline +</TITLE> +</HEAD> +<BODY> + +<H3> +PPS Clock Discipline</H3> + +<HR> +<H4> +Synopsis</H4> +Address: 127.127.22.<I>u</I> +<BR>Reference ID: <TT>PPS</TT> +<BR>Driver ID: <TT>PPS</TT> +<BR>Serial Port: <TT>/dev/pps<I>u</I></TT>; 9600 baud, 8-bits, no parity +<BR>Features: <TT>tty_clk</TT> +<H4> +Description</H4> +This driver furnishes an interface for pulse-per-second (PPS) signals produced +by a cesium clock, radio clock or related equipment. It can be used to +remove accumulated jitter and retime a secondary server when synchronized +to a primary server over a congested, wide-area network and before redistributing +the time to local clients. + +<P>In order for this driver to work, the local clock must be set to within ++-500 ms by another means, such as a radio clock or NTP itself. The PPS +signal is connected via a serial port and <A HREF="gadget.htm">gadget box</A> +consisting of a one-shot and RS232 level converter. When operated at 38.4 +kbps with a SPARCstation IPC, this arrangement has a worst-case jitter +less than 26 us. + +<P>There are three ways in which this driver can be used. The first way +uses the <TT>ppsclock</TT> line discipline and works only for the baseboard +serial ports of the Sun SPARCstation running SunOS 4.x. The PPS signal +is connected via the gadget box to the carrier detect (DCD) line of a serial +port. The signal is activated for this port by a <TT>fudge flag3 1</TT> +command following the <TT>server</TT> command in the configuration file. +This causes the <TT>ppsclock</TT> streams module to be configured for that +port and to capture a timestamp at the on-time transition of the PPS signal. +This driver then reads the timestamp directly by a designated <TT>ioctl()</TT> +system call. This provides the most accurate time and least jitter of any +other scheme. There is no need to configure a dedicated device for this +purpose, which ordinarily is the device used for the associated radio clock. + +<P>The second way uses the <TT>tty_clk</TT> line discipline and works for +any architecture supporting a serial port. If after a few seconds this +driver finds no <TT>ppsclock</TT> module configured, it attempts to open +a serial port device <TT>/dev/pps%d</TT>, where <TT>%d</TT> is the unit +number, and assign the <TT>tty_clk</TT> line discipline to it. If the line +discipline fails, no harm is done except the accuracy is reduced somewhat. +The pulse generator in the gadget box must be adjusted to produce a start +bit of length 26 usec at 38400 bps. Used with the <TT>tty_clk</TT> line +discipline, this produces an ASCII DEL character ('\377') followed by a +timestamp at the on-time transition of the PPS signal. + +<P>The third way involves an auxiliary radio clock driver which calls the +PPS driver with a timestamp captured by that driver. This use is documented +in the source code for the driver(s) involved. +<H4> +Fudge Factors</H4> + +<DL> +<DT> +<TT>time1 <I>time</I></TT></DT> + +<DD> +Specifies the time offset calibration factor, in seconds and fraction, +with default 0.0. This parameter can be used to compensate for the UART +and OS delays. Allow about 247 us for UART delays at 38400 bps and about +1 ms for SunOS streams nonsense.</DD> + +<DT> +<TT>time2 <I>time</I></TT></DT> + +<DD> +Not used by this driver.</DD> + +<DT> +<TT>stratum <I>number</I></TT></DT> + +<DD> +Specifies the driver stratum, in decimal from 0 to 15, with default 0.</DD> + +<DT> +<TT>refid <I>string</I></TT></DT> + +<DD> +Specifies the driver reference identifier, an ASCII string from one to +four characters, with default <TT>PPS</TT>.</DD> + +<DT> +<TT>flag1 0 | 1</TT></DT> + +<DD> +Not used by this driver.</DD> + +<DT> +<TT>flag2 0 | 1</TT></DT> + +<DD> +Not used by this driver.</DD> + +<DT> +<TT>flag3 0 | 1</TT></DT> + +<DD> +Not used by this driver.</DD> + +<DT> +<TT>flag4 0 | 1</TT></DT> + +<DD> +Not used by this driver.</DD> + + +<P>Additional Information + +<P><A HREF="refclock.htm">Reference Clock Drivers</A></DL> + +<HR> +<ADDRESS> +David L. Mills (mills@udel.edu)</ADDRESS> + +</BODY> +</HTML> |
