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5   <TITLE>Arbiter 1088A/B GPS Receiver
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8<BODY>
9
10<H3>
11Arbiter 1088A/B GPS Receiver</H3>
12
13<HR>
14<H4>
15Synopsis</H4>
16Address: 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>
21<H4>
22Description</H4>
23This driver supports the Arbiter 1088A/B Satellite Controlled Clock. The
24claimed accuracy of this clock is 100 ns relative to the PPS output when
25receiving four or more satellites.
26
27<P>The receiver should be configured before starting the NTP daemon, in
28order to establish reliable position and operating conditions. It does
29not initiate surveying or hold mode. For use with NTP, the daylight savings
30time feature should be disables (<TT>D0</TT> command) and the broadcast
31mode set to operate in UTC (<TT>BU</TT> command).
32
33<P>The timecode format supported by this driver is selected by the poll
34sequence <TT>B5</TT>, which initiates a line in the following format to
35be repeated once per second until turned off by the <TT>B0</TT> command.
36
37<P>Format <TT>B5</TT> (24 ASCII printing characters):
38<PRE>&lt;cr>&lt;lf>i yy ddd hh:mm:ss.000bbb
39
40on-time = &lt;cr>
41i = synchronization flag (' ' = locked, '?' = unlocked)
42yy = year of century
43ddd = day of year
44hh:mm:ss = hours, minutes, seconds
45.000 = fraction of second (not used)
46bbb = tailing spaces for fill</PRE>
47The alarm condition is indicated by a '?' at i, which indicates the receiver
48is not synchronized. In normal operation, a line consisting of the timecode
49followed by the time quality character (TQ) followed by the receiver status
50string (SR) is written to the clockstats file.
51
52<P>The time quality character is encoded in IEEE P1344 standard:
53
54<P>Format <TT>TQ</TT> (IEEE P1344 estimated worst-case time quality)
55<PRE>0&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; clock locked, maximum accuracy
56F&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; clock failure, time not reliable
574&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; clock unlocked, accuracy &lt; 1 us
585&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; clock unlocked, accuracy &lt; 10 us
596&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; clock unlocked, accuracy &lt; 100 us
607&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; clock unlocked, accuracy &lt; 1 ms
618&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; clock unlocked, accuracy &lt; 10 ms
629&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; clock unlocked, accuracy &lt; 100 ms
63A&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; clock unlocked, accuracy &lt; 1 s
64B&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; clock unlocked, accuracy &lt; 10 s</PRE>
65The status string is encoded as follows:
66
67<P>Format <TT>SR</TT> (25 ASCII printing characters)
68<PRE>V=vv S=ss T=t P=pdop E=ee
69
70vv = satellites visible
71ss = relative signal strength
72t = satellites tracked
73pdop = position dilution of precision (meters)
74ee = hardware errors</PRE>
75A three-stage median filter is used to reduce jitter and provide a dispersion
76measure. The driver makes no attempt to correct for the intrinsic jitter
77of the radio itself.
78<H4>
79Monitor Data</H4>
80When enabled by the <TT>flag4</TT> fudge flag, an additional line containing
81the latitude, longitude, elevation and optional deviation data is written
82to the <TT>clockstats</TT> file. The deviation data operates with an external
83pulse-per-second (PPS) input, such as a cesium oscillator or another radio
84clock. The PPS input should be connected to the B event channel and the
85radio initialized for deviation data on that channel. The deviation data
86consists of the mean offset and standard deviation of the external PPS
87signal relative the GPS signal, both in microseconds over the last 16 seconds.
88<H4>
89Fudge Factors</H4>
90
91<DL>
92<DT>
93<TT>time1 <I>time</I></TT></DT>
94
95<DD>
96Specifies the time offset calibration factor, in seconds and fraction,
97with default 0.0.</DD>
98
99<DT>
100<TT>time2 <I>time</I></TT></DT>
101
102<DD>
103Not used by this driver.</DD>
104
105<DT>
106<TT>stratum <I>number</I></TT></DT>
107
108<DD>
109Specifies the driver stratum, in decimal from 0 to 15, with default 0.</DD>
110
111<DT>
112<TT>refid <I>string</I></TT></DT>
113
114<DD>
115Specifies the driver reference identifier, an ASCII string from one to
116four characters, with default <TT>GPS</TT>.</DD>
117
118<DT>
119<TT>flag1 0 | 1</TT></DT>
120
121<DD>
122Not used by this driver.</DD>
123
124<DT>
125<TT>flag2 0 | 1</TT></DT>
126
127<DD>
128Not used by this driver.</DD>
129
130<DT>
131<TT>flag3 0 | 1</TT></DT>
132
133<DD>
134Not used by this driver.</DD>
135
136<DT>
137<TT>flag4 0 | 1</TT></DT>
138
139<DD>
140Enable verbose <TT>clockstats</TT> recording if set.</DD>
141</DL>
142Additional Information
143
144<P><A HREF="refclock.htm">Reference Clock Drivers</A>&nbsp;
145<HR>
146<ADDRESS>
147David L. Mills (mills@udel.edu)</ADDRESS>
148
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