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5 <TITLE>Shared memoy Driver
11 Shared Memory Driver</H3>
16 Address: 127.127.28.<I>u</I>
17 <BR>Reference ID: <TT>SHM</TT>
18 <BR>Driver ID: <TT>SHM</TT>
21 This driver receives its reference clock info from a shared memory-segment.
22 The shared memory-segment is created with owner-only access for unit 0
23 and 1, and world access for unit 2 and 3
25 Structure of shared memory-segment</H4>
28 int mode; /* 0 - if valid set
29 * use values,
30 * clear valid
31 * 1 - if valid set
32 * if count before and after read of
33 * values is equal,
34 * use values
35 * clear valid
36 */
37 int count;
38 time_t clockTimeStampSec; /* external clock */
39 int clockTimeStampUSec; /* external clock */
40 time_t receiveTimeStampSec; /* internal clock, when external value was received */
41 int receiveTimeStampUSec; /* internal clock, when external value was received */
42 int leap;
43 int precision;
44 int nsamples;
45 int valid;
46 int dummy[10];
51 When the poll-method of the driver is called, the valid-flag of the shared
52 memory-segment is checked:
54 <P>If set, the values in the record (clockTimeStampSec, clockTimeStampUSec,
55 receiveTimeStampSec, receiveTimeStampUSec, leap, precision) are passed
56 to ntp, and the valid-flag is cleared.
58 <P>If not set, a timeout is reported to ntp, nothing else happend
61 When the poll-method of the driver is called, the valid-flag of the shared
62 memory-segment is checked:
64 <P>If set, the count-field of the record is remembered, and the values
65 in the record (clockTimeStampSec, clockTimeStampUSec, receiveTimeStampSec,
66 receiveTimeStampUSec, leap, precision) are read. Then, the remembered count
67 is compared to the count now in the record. If both are equal, the values
68 read from the record are passed to ntp. If they differ, another process
69 has modified the record while it was read out (was not able to produce
70 this case), and failure is reported to ntp. The valid flag is cleared.
72 <P>If not set, a timeout is reported to ntp, nothing else happend
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>SHM</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>