| 1 | <HTML> |
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| 2 | <HEAD> |
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| 3 | <META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1"> |
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| 4 | <META NAME="GENERATOR" CONTENT="Mozilla/4.01 [en] (Win95; I) [Netscape]"> |
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| 5 | <TITLE>Trak 8820 GPS Receiver |
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| 6 | </TITLE> |
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| 7 | </HEAD> |
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| 8 | <BODY> |
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| 9 | |
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| 10 | <H3> |
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| 11 | Trak 8820 GPS Receiver</H3> |
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| 12 | |
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| 13 | <HR> |
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| 14 | <H4> |
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| 15 | Synopsis</H4> |
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| 16 | Address: 127.127.2.<I>u</I> |
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| 17 | <BR>Reference ID: <TT>GPS</TT> |
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| 18 | <BR>Driver ID: <TT>GPS_TRAK</TT> |
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| 19 | <BR>Serial Port: <TT>/dev/trak<I>u</I></TT>; 9600 baud, 8-bits, no parity |
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| 20 | <BR>Features: <TT>tty_clk</TT> |
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| 21 | <H4> |
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| 22 | Description</H4> |
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| 23 | This driver supports the Trak 8820 GPS Station Clock. The claimed accuracy |
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| 24 | at the 1-PPS output is 200-300 ns relative to the broadcast signal; however, |
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| 25 | in most cases the actual accuracy is limited by the precision of the timecode |
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| 26 | and the latencies of the serial interface and operating system. |
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| 27 | |
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| 28 | <P>For best accuracy, this radio requires the <TT>tty_clk</TT> line discipline, |
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| 29 | which captures a timestamp at the <TT>*</TT> on-time character of the timecode. |
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| 30 | Using this discipline the jitter is in the order of 1 ms and systematic |
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| 31 | error about 0.5 ms. If unavailable, the buffer timestamp is used, which |
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| 32 | is captured at the <TT>\r</TT> ending the timecode message. This introduces |
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| 33 | a systematic error of 23 character times, or about 24 ms at 9600 bps, together |
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| 34 | with a jitter well over 8 ms on Sun IPC-class machines. |
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| 35 | |
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| 36 | <P>Using the menus, the radio should be set for 9600 bps, one stop bit |
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| 37 | and no parity. It should be set to operate in computer (no echo) mode. |
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| 38 | The timecode format includes neither the year nor leap-second warning. |
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| 39 | |
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| 40 | <P>In operation, this driver sends a <TT>RQTS\r</TT> request to the radio |
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| 41 | at initialization in order to put it in continuous time output mode. The |
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| 42 | radio then sends the following message once each second: |
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| 43 | <PRE>*RQTS U,ddd:hh:mm:ss.0,q<cr><lf> |
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| 44 | |
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| 45 | on-time = '*' |
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| 46 | ddd = day of year |
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| 47 | hh:mm:ss = hours, minutes, seconds |
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| 48 | q = quality indicator (phase error), 0-6: |
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| 49 | 0 > 20 us |
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| 50 | 6 > 10 us |
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| 51 | 5 > 1 us |
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| 52 | 4 > 100 ns |
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| 53 | 3 > 10 ns |
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| 54 | 2 < 10 ns</PRE> |
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| 55 | The alarm condition is indicated by <TT>0</TT> at <TT>Q</TT>, which means |
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| 56 | the radio has a phase error greater than 20 us relative to the broadcast |
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| 57 | time. The absence of year, DST and leap-second warning in this format is |
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| 58 | also alarmed. |
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| 59 | |
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| 60 | <P>The continuous time mode is disabled using the <TT>RQTX\r</TT> request, |
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| 61 | following which the radio sends a <TT>RQTX DONE<cr><lf></TT> response. |
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| 62 | In the normal mode, other control and status requests are effective, including |
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| 63 | the leap-second status request <TT>RQLS<cr></TT>. The radio responds |
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| 64 | with <TT>RQLS yy,mm,dd<cr><lf></TT>, where <TT>yy,mm,dd</TT> are |
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| 65 | the year, month and day. Presumably, this gives the epoch of the next leap |
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| 66 | second, <TT>RQLS 00,00,00</TT> if none is specified in the GPS message. |
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| 67 | Specified in this form, the information is generally useless and is ignored |
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| 68 | by the driver. |
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| 69 | <H4> |
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| 70 | Monitor Data</H4> |
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| 71 | When enabled by the <TT>flag4</TT> fudge flag, every received timecode |
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| 72 | is written as-is to the <TT>clockstats</TT> file. |
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| 73 | <H4> |
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| 74 | Fudge Factors</H4> |
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| 75 | |
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| 76 | <DL> |
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| 77 | <DT> |
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| 78 | <TT>time1 <I>time</I></TT></DT> |
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| 79 | |
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| 80 | <DD> |
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| 81 | Specifies the time offset calibration factor, in seconds and fraction, |
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| 82 | with default 0.0.</DD> |
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| 83 | |
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| 84 | <DT> |
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| 85 | <TT>time2 <I>time</I></TT></DT> |
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| 86 | |
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| 87 | <DD> |
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| 88 | Not used by this driver.</DD> |
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| 89 | |
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| 90 | <DT> |
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| 91 | <TT>stratum <I>number</I></TT></DT> |
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| 92 | |
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| 93 | <DD> |
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| 94 | Specifies the driver stratum, in decimal from 0 to 15, with default 0.</DD> |
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| 95 | |
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| 96 | <DT> |
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| 97 | <TT>refid <I>string</I></TT></DT> |
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| 98 | |
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| 99 | <DD> |
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| 100 | Specifies the driver reference identifier, an ASCII string from one to |
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| 101 | four characters, with default <TT>GPS</TT>.</DD> |
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| 102 | |
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| 103 | <DT> |
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| 104 | <TT>flag1 0 | 1</TT></DT> |
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| 105 | |
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| 106 | <DD> |
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| 107 | Not used by this driver.</DD> |
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| 108 | |
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| 109 | <DT> |
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| 110 | <TT>flag2 0 | 1</TT></DT> |
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| 111 | |
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| 112 | <DD> |
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| 113 | Not used by this driver.</DD> |
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| 114 | |
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| 115 | <DT> |
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| 116 | <TT>flag3 0 | 1</TT></DT> |
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| 117 | |
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| 118 | <DD> |
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| 119 | Not used by this driver.</DD> |
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| 120 | |
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| 121 | <DT> |
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| 122 | <TT>flag4 0 | 1</TT></DT> |
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| 123 | |
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| 124 | <DD> |
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| 125 | Not used by this driver.</DD> |
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| 126 | |
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| 127 | |
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| 128 | <P>Additional Information |
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| 129 | |
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| 130 | <P><A HREF="refclock.htm">Reference Clock Drivers</A></DL> |
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| 131 | |
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| 132 | <HR> |
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| 133 | <ADDRESS> |
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| 134 | David L. Mills (mills@udel.edu)</ADDRESS> |
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| 135 | |
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| 136 | </BODY> |
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| 137 | </HTML> |
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