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5 | <TITLE>Arbiter 1088A/B 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 | Arbiter 1088A/B 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: 127.127.11.<I>u</I> |
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17 | <BR>Reference ID: <TT>GPS</TT> |
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18 | <BR>Driver ID: <TT>GPS_ARBITER</TT> |
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19 | <BR>Serial Port: <TT>/dev/gps<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 Arbiter 1088A/B Satellite Controlled Clock. The |
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24 | claimed accuracy of this clock is 100 ns relative to the PPS output when |
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25 | receiving four or more satellites. |
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26 | |
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27 | <P>The receiver should be configured before starting the NTP daemon, in |
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28 | order to establish reliable position and operating conditions. It does |
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29 | not initiate surveying or hold mode. For use with NTP, the daylight savings |
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30 | time feature should be disables (<TT>D0</TT> command) and the broadcast |
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31 | mode set to operate in UTC (<TT>BU</TT> command). |
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32 | |
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33 | <P>The timecode format supported by this driver is selected by the poll |
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34 | sequence <TT>B5</TT>, which initiates a line in the following format to |
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35 | be repeated once per second until turned off by the <TT>B0</TT> command. |
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36 | |
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37 | <P>Format <TT>B5</TT> (24 ASCII printing characters): |
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38 | <PRE><cr><lf>i yy ddd hh:mm:ss.000bbb |
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39 | |
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40 | on-time = <cr> |
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41 | i = synchronization flag (' ' = locked, '?' = unlocked) |
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42 | yy = year of century |
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43 | ddd = day of year |
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44 | hh:mm:ss = hours, minutes, seconds |
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45 | .000 = fraction of second (not used) |
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46 | bbb = tailing spaces for fill</PRE> |
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47 | The alarm condition is indicated by a '?' at i, which indicates the receiver |
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48 | is not synchronized. In normal operation, a line consisting of the timecode |
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49 | followed by the time quality character (TQ) followed by the receiver status |
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50 | string (SR) is written to the clockstats file. |
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51 | |
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52 | <P>The time quality character is encoded in IEEE P1344 standard: |
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53 | |
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54 | <P>Format <TT>TQ</TT> (IEEE P1344 estimated worst-case time quality) |
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55 | <PRE>0 clock locked, maximum accuracy |
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56 | F clock failure, time not reliable |
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57 | 4 clock unlocked, accuracy < 1 us |
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58 | 5 clock unlocked, accuracy < 10 us |
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59 | 6 clock unlocked, accuracy < 100 us |
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60 | 7 clock unlocked, accuracy < 1 ms |
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61 | 8 clock unlocked, accuracy < 10 ms |
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62 | 9 clock unlocked, accuracy < 100 ms |
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63 | A clock unlocked, accuracy < 1 s |
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64 | B clock unlocked, accuracy < 10 s</PRE> |
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65 | The status string is encoded as follows: |
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66 | |
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67 | <P>Format <TT>SR</TT> (25 ASCII printing characters) |
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68 | <PRE>V=vv S=ss T=t P=pdop E=ee |
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69 | |
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70 | vv = satellites visible |
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71 | ss = relative signal strength |
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72 | t = satellites tracked |
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73 | pdop = position dilution of precision (meters) |
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74 | ee = hardware errors</PRE> |
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75 | A three-stage median filter is used to reduce jitter and provide a dispersion |
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76 | measure. The driver makes no attempt to correct for the intrinsic jitter |
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77 | of the radio itself. |
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78 | <H4> |
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79 | Monitor Data</H4> |
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80 | When enabled by the <TT>flag4</TT> fudge flag, an additional line containing |
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81 | the latitude, longitude, elevation and optional deviation data is written |
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82 | to the <TT>clockstats</TT> file. The deviation data operates with an external |
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83 | pulse-per-second (PPS) input, such as a cesium oscillator or another radio |
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84 | clock. The PPS input should be connected to the B event channel and the |
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85 | radio initialized for deviation data on that channel. The deviation data |
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86 | consists of the mean offset and standard deviation of the external PPS |
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87 | signal relative the GPS signal, both in microseconds over the last 16 seconds. |
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88 | <H4> |
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89 | Fudge Factors</H4> |
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90 | |
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91 | <DL> |
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92 | <DT> |
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93 | <TT>time1 <I>time</I></TT></DT> |
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94 | |
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95 | <DD> |
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96 | Specifies the time offset calibration factor, in seconds and fraction, |
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97 | with default 0.0.</DD> |
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98 | |
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99 | <DT> |
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100 | <TT>time2 <I>time</I></TT></DT> |
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101 | |
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102 | <DD> |
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103 | Not used by this driver.</DD> |
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104 | |
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105 | <DT> |
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106 | <TT>stratum <I>number</I></TT></DT> |
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107 | |
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108 | <DD> |
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109 | Specifies the driver stratum, in decimal from 0 to 15, with default 0.</DD> |
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110 | |
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111 | <DT> |
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112 | <TT>refid <I>string</I></TT></DT> |
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113 | |
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114 | <DD> |
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115 | Specifies the driver reference identifier, an ASCII string from one to |
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116 | four characters, with default <TT>GPS</TT>.</DD> |
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117 | |
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118 | <DT> |
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119 | <TT>flag1 0 | 1</TT></DT> |
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120 | |
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121 | <DD> |
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122 | Not used by this driver.</DD> |
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123 | |
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124 | <DT> |
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125 | <TT>flag2 0 | 1</TT></DT> |
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126 | |
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127 | <DD> |
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128 | Not used by this driver.</DD> |
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129 | |
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130 | <DT> |
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131 | <TT>flag3 0 | 1</TT></DT> |
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132 | |
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133 | <DD> |
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134 | Not used by this driver.</DD> |
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135 | |
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136 | <DT> |
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137 | <TT>flag4 0 | 1</TT></DT> |
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138 | |
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139 | <DD> |
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140 | Enable verbose <TT>clockstats</TT> recording if set.</DD> |
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141 | </DL> |
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142 | Additional Information |
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143 | |
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144 | <P><A HREF="refclock.htm">Reference Clock Drivers</A> |
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145 | <HR> |
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146 | <ADDRESS> |
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147 | David L. Mills (mills@udel.edu)</ADDRESS> |
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148 | |
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149 | </BODY> |
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150 | </HTML> |
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