97 lines
4.1 KiB
Plaintext
97 lines
4.1 KiB
Plaintext
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PARSE reference clock driver:
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This directory contains the files making up the parser for
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the parse refclock driver. For reasonably sane clocks this refclock
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drivers allows a refclock implementation by just providing a
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conversion routine and the appropriate NTP parameters. Refclock
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support can run as low a 3k code with the parse refclock driver.
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The modules in here are designed to live in two worlds. In userlevel
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as part of the xntp daemon and in kernel land as part of a STREAMS module
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or, if someone gets to it, as part of a line discipline. Currently only
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SunOS4.x/SunOS5.x STREAMS are supported (volunteers for other vendors like HP?).
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This structure means, that refclock_parse can work with or without kernel
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support. Kernelsupport increases accuracy tremendingly. The current restriction
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of the parse driver is that it only supports SYSV type ttys and that kernel
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support is only available for Suns right now.
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Three kernel modules are part of this directory. These work only on
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SunOS (SunOS4 and SunOS5).
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SunOS4 (aka Solaris 1.x):
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parsestreams.loadable_module.o - standard parse module for SunOS 4
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Both modules can be loaded via modload <modulename>.
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SunOS5 (aka Solaris 2.x):
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parse - auto loadable streams module
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To install just drop "parse" into /kernel/strmod and
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start the daemon (SunOS5 will do the rest).
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The structure of the parse reference clock driver is as follows:
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xntpd - contains NTP implementation and calls a reference clock
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127.127.8.x which is implemented by
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refclock_parse.c
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- which contains several refclock decriptions. These are
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selected by the x part of the refclock address.
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The lower two bits specify the device to use. Thus the
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value (x % 4) determines the device to open
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(/dev/refclock-0 - /dev/refclock-3).
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The kind of clock is selected by the mode parameter. This parameter
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selects the clock type which deterimines how I/O is done,
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the tty parameters and the NTP parameters.
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refclock_parse operates on an abstract reference clock
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that delivers time stamps and stati. Offsets and sychron-
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isation information is derived from this data and passed
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on to refclock_receive of xntp which uses that data for
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syncronisation.
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The abstract reference clock is generated by the parse*
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routines. They parse the incoming data stream from the
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clock and convert it to the appropriate time stamps.
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The data is also mapped int the abstract clock states
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POWERUP - clock has no valid phase and time code
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information
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NOSYNC - Time code is not confirmed, phase is probably
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ok.
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SYNC - Time code and phase are correct.
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A clock is trusted for a certain time (type parameter) when
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it leaves the SYNC state. This is derived from the
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observation that quite a few clocks can still generate good
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time code information when losing contact to their
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synchronisation source. When the clock does not reagain
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synchronisation in that trust period it will be deemed
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unsynchronised until it regains synchronisation. The same
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will happen if xntp sees the clock unsynchronised at
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startup.
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The upper bit of x specifies that all samples delivered
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from the clock should be used to discipline the NTP
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loopfilter. For clock with accurate once a second time
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information this means big improvements for time keeping.
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A prerequisite for passing on the time stamps to
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the loopfilter is, that the clock is in synchronised state.
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parse.c These are the general routines to parse the incoming data
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stream. Usually these routines should not require
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modification.
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clk_*.c These files hole the conversion code for the time stamps
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and the description how the time code can be parsed and
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where the time stamps are to be taken.
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If you want to add a new clock type this is the file
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you need to write in addition to mention it in
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parse_conf.c and setting up the NTP and TTY parameters
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in refclock_parse.c.
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Further information can be found in parse/README.parse and the various source
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files.
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Frank Kardel
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