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5 <TITLE>Trak 8820 GPS Receiver
11 Trak 8820 GPS Receiver</H3>
16 Address: 127.127.2.<I>u</I>
17 <BR>Reference ID: <TT>GPS</TT>
18 <BR>Driver ID: <TT>GPS_TRAK</TT>
19 <BR>Serial Port: <TT>/dev/trak<I>u</I></TT>; 9600 baud, 8-bits, no parity
20 <BR>Features: <TT>tty_clk</TT>
23 This driver supports the Trak 8820 GPS Station Clock. The claimed accuracy
24 at the 1-PPS output is 200-300 ns relative to the broadcast signal; however,
25 in most cases the actual accuracy is limited by the precision of the timecode
26 and the latencies of the serial interface and operating system.
28 <P>For best accuracy, this radio requires the <TT>tty_clk</TT> line discipline,
29 which captures a timestamp at the <TT>*</TT> on-time character of the timecode.
30 Using this discipline the jitter is in the order of 1 ms and systematic
31 error about 0.5 ms. If unavailable, the buffer timestamp is used, which
32 is captured at the <TT>\r</TT> ending the timecode message. This introduces
33 a systematic error of 23 character times, or about 24 ms at 9600 bps, together
34 with a jitter well over 8 ms on Sun IPC-class machines.
36 <P>Using the menus, the radio should be set for 9600 bps, one stop bit
37 and no parity. It should be set to operate in computer (no echo) mode.
38 The timecode format includes neither the year nor leap-second warning.
40 <P>In operation, this driver sends a <TT>RQTS\r</TT> request to the radio
41 at initialization in order to put it in continuous time output mode. The
42 radio then sends the following message once each second:
43 <PRE>*RQTS U,ddd:hh:mm:ss.0,q<cr><lf>
47 hh:mm:ss = hours, minutes, seconds
48 q = quality indicator (phase error), 0-6:
49 0 > 20 us
50 6 > 10 us
51 5 > 1 us
52 4 > 100 ns
53 3 > 10 ns
54 2 < 10 ns</PRE>
55 The alarm condition is indicated by <TT>0</TT> at <TT>Q</TT>, which means
56 the radio has a phase error greater than 20 us relative to the broadcast
57 time. The absence of year, DST and leap-second warning in this format is
60 <P>The continuous time mode is disabled using the <TT>RQTX\r</TT> request,
61 following which the radio sends a <TT>RQTX DONE<cr><lf></TT> response.
62 In the normal mode, other control and status requests are effective, including
63 the leap-second status request <TT>RQLS<cr></TT>. The radio responds
64 with <TT>RQLS yy,mm,dd<cr><lf></TT>, where <TT>yy,mm,dd</TT> are
65 the year, month and day. Presumably, this gives the epoch of the next leap
66 second, <TT>RQLS 00,00,00</TT> if none is specified in the GPS message.
67 Specified in this form, the information is generally useless and is ignored
71 When enabled by the <TT>flag4</TT> fudge flag, every received timecode
72 is written as-is to the <TT>clockstats</TT> file.
78 <TT>time1 <I>time</I></TT></DT>
81 Specifies the time offset calibration factor, in seconds and fraction,
82 with default 0.0.</DD>
85 <TT>time2 <I>time</I></TT></DT>
88 Not used by this driver.</DD>
91 <TT>stratum <I>number</I></TT></DT>
94 Specifies the driver stratum, in decimal from 0 to 15, with default 0.</DD>
97 <TT>refid <I>string</I></TT></DT>
100 Specifies the driver reference identifier, an ASCII string from one to
101 four characters, with default <TT>GPS</TT>.</DD>
104 <TT>flag1 0 | 1</TT></DT>
107 Not used by this driver.</DD>
110 <TT>flag2 0 | 1</TT></DT>
113 Not used by this driver.</DD>
116 <TT>flag3 0 | 1</TT></DT>
119 Not used by this driver.</DD>
122 <TT>flag4 0 | 1</TT></DT>
125 Not used by this driver.</DD>
128 <P>Additional Information
130 <P><A HREF="refclock.htm">Reference Clock Drivers</A></DL>
134 David L. Mills (mills@udel.edu)</ADDRESS>