134 lines
4.4 KiB
HTML
134 lines
4.4 KiB
HTML
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<HTML>
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<HEAD>
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<META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1">
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<META NAME="GENERATOR" CONTENT="Mozilla/4.01 [en] (Win95; I) [Netscape]">
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<TITLE>Shared memoy Driver
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</TITLE>
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</HEAD>
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<BODY>
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<H3>
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Shared Memory Driver</H3>
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<HR>
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<H4>
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Synopsis</H4>
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Address: 127.127.28.<I>u</I>
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<BR>Reference ID: <TT>SHM</TT>
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<BR>Driver ID: <TT>SHM</TT>
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<H4>
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Description</H4>
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This driver receives its reference clock info from a shared memory-segment.
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The shared memory-segment is created with owner-only access for unit 0
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and 1, and world access for unit 2 and 3
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<H4>
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Structure of shared memory-segment</H4>
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<PRE>struct shmTime {
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int mode; /* 0 - if valid set
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* use values,
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* clear valid
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* 1 - if valid set
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* if count before and after read of
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* values is equal,
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* use values
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* clear valid
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*/
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int count;
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time_t clockTimeStampSec; /* external clock */
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int clockTimeStampUSec; /* external clock */
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time_t receiveTimeStampSec; /* internal clock, when external value was received */
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int receiveTimeStampUSec; /* internal clock, when external value was received */
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int leap;
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int precision;
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int nsamples;
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int valid;
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int dummy[10];
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};</PRE>
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<H4>
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Operation mode=0</H4>
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When the poll-method of the driver is called, the valid-flag of the shared
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memory-segment is checked:
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<P>If set, the values in the record (clockTimeStampSec, clockTimeStampUSec,
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receiveTimeStampSec, receiveTimeStampUSec, leap, precision) are passed
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to ntp, and the valid-flag is cleared.
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<P>If not set, a timeout is reported to ntp, nothing else happend
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<H4>
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Operation mode=1</H4>
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When the poll-method of the driver is called, the valid-flag of the shared
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memory-segment is checked:
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<P>If set, the count-field of the record is remembered, and the values
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in the record (clockTimeStampSec, clockTimeStampUSec, receiveTimeStampSec,
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receiveTimeStampUSec, leap, precision) are read. Then, the remembered count
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is compared to the count now in the record. If both are equal, the values
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read from the record are passed to ntp. If they differ, another process
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has modified the record while it was read out (was not able to produce
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this case), and failure is reported to ntp. The valid flag is cleared.
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<P>If not set, a timeout is reported to ntp, nothing else happend
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<H4>
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Fudge Factors</H4>
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<DL>
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<DT>
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<TT>time1 <I>time</I></TT></DT>
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<DD>
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Specifies the time offset calibration factor, in seconds and fraction,
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with default 0.0.</DD>
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<DT>
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<TT>time2 <I>time</I></TT></DT>
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<DD>
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Not used by this driver.</DD>
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<DT>
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<TT>stratum <I>number</I></TT></DT>
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<DD>
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Specifies the driver stratum, in decimal from 0 to 15, with default 0.</DD>
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<DT>
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<TT>refid <I>string</I></TT></DT>
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<DD>
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Specifies the driver reference identifier, an ASCII string from one to
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four characters, with default <TT>SHM</TT>.</DD>
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<DT>
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<TT>flag1 0 | 1</TT></DT>
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<DD>
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Not used by this driver.</DD>
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<DT>
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<TT>flag2 0 | 1</TT></DT>
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<DD>
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Not used by this driver.</DD>
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<DT>
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<TT>flag3 0 | 1</TT></DT>
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<DD>
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Not used by this driver.</DD>
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<DT>
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<TT>flag4 0 | 1</TT></DT>
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<DD>
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Not used by this driver.</DD>
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<P>Additional Information
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<P><A HREF="refclock.htm">Reference Clock Drivers</A></DL>
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</BODY>
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</HTML>
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