README
1PARSE reference clock driver:
2
3This directory contains the files making up the parser for
4the parse refclock driver. For reasonably sane clocks this refclock
5drivers allows a refclock implementation by just providing a
6conversion routine and the appropriate NTP parameters. Refclock
7support can run as low a 3k code with the parse refclock driver.
8
9The modules in here are designed to live in two worlds. In userlevel
10as part of the xntp daemon and in kernel land as part of a STREAMS module
11or, if someone gets to it, as part of a line discipline. Currently only
12SunOS4.x/SunOS5.x STREAMS are supported (volunteers for other vendors like HP?).
13This structure means, that refclock_parse can work with or without kernel
14support. Kernelsupport increases accuracy tremendingly. The current restriction
15of the parse driver is that it only supports SYSV type ttys and that kernel
16support is only available for Suns right now.
17
18Three kernel modules are part of this directory. These work only on
19SunOS (SunOS4 and SunOS5).
20
21 SunOS4 (aka Solaris 1.x):
22 parsestreams.loadable_module.o - standard parse module for SunOS 4
23
24 Both modules can be loaded via modload <modulename>.
25
26 SunOS5 (aka Solaris 2.x):
27 parse - auto loadable streams module
28
29 To install just drop "parse" into /kernel/strmod and
30 start the daemon (SunOS5 will do the rest).
31
32The structure of the parse reference clock driver is as follows:
33
34 ntpd - contains NTP implementation and calls a reference clock
35 127.127.8.x which is implemented by
36 refclock_parse.c
37 - which contains several refclock decriptions. These are
38 selected by the x part of the refclock address.
39 The lower two bits specify the device to use. Thus the
40 value (x % 4) determines the device to open
41 (/dev/refclock-0 - /dev/refclock-3).
42
43 The kind of clock is selected by the mode parameter. This parameter
44 selects the clock type which deterimines how I/O is done,
45 the tty parameters and the NTP parameters.
46
47 refclock_parse operates on an abstract reference clock
48 that delivers time stamps and stati. Offsets and sychron-
49 isation information is derived from this data and passed
50 on to refclock_receive of xntp which uses that data for
51 syncronisation.
52
53 The abstract reference clock is generated by the parse*
54 routines. They parse the incoming data stream from the
55 clock and convert it to the appropriate time stamps.
56 The data is also mapped int the abstract clock states
57 POWERUP - clock has no valid phase and time code
58 information
59
60 NOSYNC - Time code is not confirmed, phase is probably
61 ok.
62 SYNC - Time code and phase are correct.
63
64 A clock is trusted for a certain time (type parameter) when
65 it leaves the SYNC state. This is derived from the
66 observation that quite a few clocks can still generate good
67 time code information when losing contact to their
68 synchronisation source. When the clock does not reagain
69 synchronisation in that trust period it will be deemed
70 unsynchronised until it regains synchronisation. The same
71 will happen if xntp sees the clock unsynchronised at
72 startup.
73
74 The upper bit of x specifies that all samples delivered
75 from the clock should be used to discipline the NTP
76 loopfilter. For clock with accurate once a second time
77 information this means big improvements for time keeping.
78 A prerequisite for passing on the time stamps to
79 the loopfilter is, that the clock is in synchronised state.
80
81 parse.c These are the general routines to parse the incoming data
82 stream. Usually these routines should not require
83 modification.
84
85 clk_*.c These files hole the conversion code for the time stamps
86 and the description how the time code can be parsed and
87 where the time stamps are to be taken.
88 If you want to add a new clock type this is the file
89 you need to write in addition to mention it in
90 parse_conf.c and setting up the NTP and TTY parameters
91 in refclock_parse.c.
92
93Further information can be found in parse/README.parse and the various source
94files.
95
96Frank Kardel
97