<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>Spectracom 8170 and Netclock/2 WWVB Receivers </TITLE> </HEAD> <BODY> <H3> Spectracom 8170 and Netclock/2 WWVB Receivers</H3> <HR> <H4> Synopsis</H4> Address: 127.127.4.<I>u</I> <BR>Reference ID: <TT>WWVB</TT> <BR>Driver ID: <TT>WWVB_SPEC</TT> <BR>Serial Port: <TT>/dev/wwvb<I>u</I></TT>; 9600 baud, 8-bits, no parity <BR>Features: <TT>tty_clk</TT> <H4> Description</H4> This driver supports the Spectracom Model 8170 and Netclock/2 WWVB Synchronized Clock. This clock has proven a reliable source of time, except in some cases of high ambient conductive RF interference. The claimed accuracy of the clock is 100 usec relative to the broadcast signal; however, in most cases the actual accuracy is limited by the precision of the timecode and the latencies of the serial interface and operating system. <P>The DIPswitches on this clock should be set to 24-hour display, AUTO DST off, data format 0 or 2 (see below) and baud rate 9600. If this clock is to used as the source for the IRIG Audio Decoder (refclock_irig.c in this distribution), set the DIPswitches for AM IRIG output and IRIG format 1 (IRIG B with signature control). <P>There are two timecode formats used by these clocks. Format 0, which is available with both the Netclock/2 and 8170, and format 2, which is available only with the Netclock/2 and specially modified 8170. <P>Format 0 (22 ASCII printing characters): <PRE><cr><lf>i ddd hh:mm:ss TZ=zz<cr><lf> on-time = first <cr> i = synchronization flag (' ' = in synch, '?' = out synch) hh:mm:ss = hours, minutes, seconds</PRE> The alarm condition is indicated by other than ' ' at <TT>i</TT>, which occurs during initial synchronization and when received signal is lost for about ten hours. <P>Format 2 (24 ASCII printing characters): <PRE><cr><lf>iqyy ddd hh:mm:ss.fff ld on-time = <cr> i = synchronization flag (' ' = in synch, '?' = out synch) q = quality indicator (' ' = locked, 'A'...'D' = unlocked) yy = year (as broadcast) ddd = day of year hh:mm:ss.fff = hours, minutes, seconds, milliseconds</PRE> The alarm condition is indicated by other than ' ' at <TT>i</TT>, which occurs during initial synchronization and when received signal is lost for about ten hours. The unlock condition is indicated by other than ' ' at <TT>q</TT>. <P>The <TT>q</TT> is normally ' ' when the time error is less than 1 ms and a character in the set <TT>A...D</TT> when the time error is less than 10, 100, 500 and greater than 500 ms respectively. The <TT>l</TT> is normally ' ', but is set to <TT>L</TT> early in the month of an upcoming UTC leap second and reset to ' ' on the first day of the following month. The <TT>d</TT> is set to <TT>S</TT> for standard time <TT>S</TT>, <TT>I</TT> on the day preceding a switch to daylight time, <TT>D</TT> for daylight time and <TT>O</TT> on the day preceding a switch to standard time. The start bit of the first <cr> is synchronized to the indicated time as returned. <P>This driver does not need to be told which format is in use - it figures out which one from the length of the message. A three-stage median filter is used to reduce jitter and provide a dispersion measure. The driver makes no attempt to correct for the intrinsic jitter of the radio itself, which is a known problem with the older radios. <H4> Monitor Data</H4> The driver writes each timecode as received to the <TT>clockstats</TT> file. When enabled by the <TT>flag4</TT> fudge flag, a table of quality data maintained internally by the Netclock/2 is retrieved and written to the <TT>clockstats</TT> file when the first timecode message of a new day is received. <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.</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>WWVB</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> Enable verbose <TT>clockstats</TT> recording if set.</DD> </DL> Additional Information <P><A HREF="refclock.htm">Reference Clock Drivers</A> <HR> <ADDRESS> David L. Mills (mills@udel.edu)</ADDRESS> </BODY> </HTML>