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diff --git a/usr.sbin/xntpd/parse/README b/usr.sbin/xntpd/parse/README new file mode 100644 index 0000000..aa83aa7 --- /dev/null +++ b/usr.sbin/xntpd/parse/README @@ -0,0 +1,100 @@ +PARSE reference clock driver: + +This directory contains the files making up the parser for +the parse refclock driver. For reasonably sane clocks this refclock +drivers allows a refclock implementation by just providing a +conversion routine and the appropriate NTP parameters. Refclock +support can run as low a 3k code with the parse refclock driver. + +The modules in here are designed to live in two worlds. In userlevel +as part of the xntp daemon and in kernel land as part of a STREAMS module +or, if someone gets to it, as part of a line discipline. Currently only +SunOS4.x/SunOS5.x STREAMS are supported (volunteers for other vendors like HP?). +This structure means, that refclock_parse can work with or without kernel +support. Kernelsupport increases accuracy tremendingly. The current restriction +of the parse driver is that it only supports SYSV type ttys and that kernel +support is only available for Suns right now. + +Three kernel modules are part of this directory. These work only on +SunOS (SunOS4 and SunOS5 (not fully tested!)). + + SunOS4 (aka Solaris 1.x): + parsestreams.o - standard parse module for SunOS 4 + mparsestreams.o - parse module for SunOS 4 with better + clock reading code (assembler) + + Both modules can be loaded via modload <modulename>. + + SunOS5 (aka Solaris 2.x): + parse - auto loadable streams module + (not fully tested - don't kill me if + it kills you machine) + + To install just drop "parse" into /kernel/strmod and + start the daemon (SunOS5 will do the rest). + +The structure of the parse reference clock driver is as follows: + + xntpd - contains NTP implementation and calls a reference clock + 127.127.8.x which is implemented by + refclock_parse.c + - which contains several refclock decriptions. These are + selected by the x part of the refclock address. + The lower two bits specify the device to use. Thus the + value (x % 4) determines the device to open + (/dev/refclock-0 - /dev/refclock-3). + + The kind of clock is selected by bits 2-6. This parameter + selects the clock type which deterimines how I/O is done, + the tty parameters and the NTP parameters. + + refclock_parse operates on an abstract reference clock + that delivers time stamps and stati. Offsets and sychron- + isation information is derived from this data and passed + on to refclock_receive of xntp which uses that data for + syncronisation. + + The abstract reference clock is generated by the parse* + routines. They parse the incoming data stream from the + clock and convert it to the appropriate time stamps. + The data is also mapped int the abstract clock states + POWERUP - clock has no valid phase and time code + information + + NOSYNC - Time code is not confirmed, phase is probably + ok. + SYNC - Time code and phase are correct. + + A clock is trusted for a certain time (type parameter) when + it leaves the SYNC state. This is derived from the + observation that quite a few clocks can still generate good + time code information when losing contact to their + synchronisation source. When the clock does not reagain + synchronisation in that trust period it will be deemed + unsynchronised until it regains synchronisation. The same + will happen if xntp sees the clock unsynchronised at + startup. + + The upper bit of x specifies that all samples delivered + from the clock should be used to discipline the NTP + loppfilter. For clock with accurate once a second time + information this means big improvements for time keeping. + A prerequisite for passing on the time stamps to + the loopfilter is, that the clock is in synchronised state. + + parse.c These are the general routines to parse the incoming data + stream. Usually these routines should not require + modification. + + clk_*.c These files hole the conversion code for the time stamps + and the description how the time code can be parsed and + where the time stamps are to be taken. + If you want to add a new clock type this is the file + you need to write in addition to mention it in + parse_conf.c and setting up the NTP and TTY parameters + in refclock_parse.c. + +Further information can be found in parse/README.parse and the various source +files. + +Frank Kardel |
