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5 <TITLE>Arbiter 1088A/B GPS Receiver
11 Arbiter 1088A/B GPS Receiver</H3>
16 Address: 127.127.11.<I>u</I>
17 <BR>Reference ID: <TT>GPS</TT>
18 <BR>Driver ID: <TT>GPS_ARBITER</TT>
19 <BR>Serial Port: <TT>/dev/gps<I>u</I></TT>; 9600 baud, 8-bits, no parity
20 <BR>Features: <TT>tty_clk</TT>
23 This driver supports the Arbiter 1088A/B Satellite Controlled Clock. The
24 claimed accuracy of this clock is 100 ns relative to the PPS output when
25 receiving four or more satellites.
27 <P>The receiver should be configured before starting the NTP daemon, in
28 order to establish reliable position and operating conditions. It does
29 not initiate surveying or hold mode. For use with NTP, the daylight savings
30 time feature should be disables (<TT>D0</TT> command) and the broadcast
31 mode set to operate in UTC (<TT>BU</TT> command).
33 <P>The timecode format supported by this driver is selected by the poll
34 sequence <TT>B5</TT>, which initiates a line in the following format to
35 be repeated once per second until turned off by the <TT>B0</TT> command.
37 <P>Format <TT>B5</TT> (24 ASCII printing characters):
38 <PRE><cr><lf>i yy ddd hh:mm:ss.000bbb
41 i = synchronization flag (' ' = locked, '?' = unlocked)
44 hh:mm:ss = hours, minutes, seconds
45 .000 = fraction of second (not used)
46 bbb = tailing spaces for fill</PRE>
47 The alarm condition is indicated by a '?' at i, which indicates the receiver
48 is not synchronized. In normal operation, a line consisting of the timecode
49 followed by the time quality character (TQ) followed by the receiver status
50 string (SR) is written to the clockstats file.
52 <P>The time quality character is encoded in IEEE P1344 standard:
54 <P>Format <TT>TQ</TT> (IEEE P1344 estimated worst-case time quality)
55 <PRE>0 clock locked, maximum accuracy
56 F clock failure, time not reliable
57 4 clock unlocked, accuracy < 1 us
58 5 clock unlocked, accuracy < 10 us
59 6 clock unlocked, accuracy < 100 us
60 7 clock unlocked, accuracy < 1 ms
61 8 clock unlocked, accuracy < 10 ms
62 9 clock unlocked, accuracy < 100 ms
63 A clock unlocked, accuracy < 1 s
64 B clock unlocked, accuracy < 10 s</PRE>
65 The status string is encoded as follows:
67 <P>Format <TT>SR</TT> (25 ASCII printing characters)
68 <PRE>V=vv S=ss T=t P=pdop E=ee
70 vv = satellites visible
71 ss = relative signal strength
72 t = satellites tracked
73 pdop = position dilution of precision (meters)
74 ee = hardware errors</PRE>
75 A three-stage median filter is used to reduce jitter and provide a dispersion
76 measure. The driver makes no attempt to correct for the intrinsic jitter
80 When enabled by the <TT>flag4</TT> fudge flag, an additional line containing
81 the latitude, longitude, elevation and optional deviation data is written
82 to the <TT>clockstats</TT> file. The deviation data operates with an external
83 pulse-per-second (PPS) input, such as a cesium oscillator or another radio
84 clock. The PPS input should be connected to the B event channel and the
85 radio initialized for deviation data on that channel. The deviation data
86 consists of the mean offset and standard deviation of the external PPS
87 signal relative the GPS signal, both in microseconds over the last 16 seconds.
93 <TT>time1 <I>time</I></TT></DT>
96 Specifies the time offset calibration factor, in seconds and fraction,
97 with default 0.0.</DD>
100 <TT>time2 <I>time</I></TT></DT>
103 Not used by this driver.</DD>
106 <TT>stratum <I>number</I></TT></DT>
109 Specifies the driver stratum, in decimal from 0 to 15, with default 0.</DD>
112 <TT>refid <I>string</I></TT></DT>
115 Specifies the driver reference identifier, an ASCII string from one to
116 four characters, with default <TT>GPS</TT>.</DD>
119 <TT>flag1 0 | 1</TT></DT>
122 Not used by this driver.</DD>
125 <TT>flag2 0 | 1</TT></DT>
128 Not used by this driver.</DD>
131 <TT>flag3 0 | 1</TT></DT>
134 Not used by this driver.</DD>
137 <TT>flag4 0 | 1</TT></DT>
140 Enable verbose <TT>clockstats</TT> recording if set.</DD>
142 Additional Information
144 <P><A HREF="refclock.htm">Reference Clock Drivers</A>
147 David L. Mills (mills@udel.edu)</ADDRESS>