README file for directory ./util of the NTP Version 3 distribution

This directory contains the sources for the various utility programs. See
the README and RELNOTES files in the parent directory for directions on
how to make and install these programs.

The jitter.c program can be used to determine the timing jitter due to
the operating system in a gettimeofday() call. For most systems the
dominant contribution to the jitter budget is the period of the hardware
interrupt, usually in the range 1-10 ms. For thos systems with microsecond
counters, such as recent Sun and certain Ultrix systems, the jitter is
dominated only by the operating system and is in the range 20-60 usec. 

The timetrim.c program can be used with SGI machines to implement a
scheme to discipline the hardware clock frequency. See the source code
for further information.

The byteorder.c and longsize.c programs are used during the configuration
process to determine the byte order (little or big endian) and longword
size (32 or 64 bits). See the ../scripts/makefile.sh script for further
details.

The testrs6000.c program is used for testing purposes with the IBM
RS/6000 AIX machines. Bill Jones <jones@chpc.utexas.edu> reports:
"I could not get a tickadj of less then 40 us to work on a RS6000.
If you set it less then 40 us do so at your own risk!"

The tickadj.c program can be used to read and set various kernel
parameters affecting NTP operations. Comes now the rationale for its use.

Then daemon's clock adjustment algorithms depend (too) strongly
on the internals of the kernel adjtime() call, and expect it to
match that which comes with Berkeley-flavour operating systems.
The daemon actually reads a couple of values from your kernel
using /dev/kmem (ugh!), the value of `tick' and the value of `tickadj'.
`tick' is expected to be the number of microseconds which are
added to the system time on timer interrupts when the clock isn't
being slewed.  `tickadj' is the number of microseconds which are
added or subtracted from tick when the clock is being slewed.

The program tickadj mimics the daemon's handling of these variables.
If you run it (as root) and it fails or produces bizarre looking
values you may have to torque ntp_unixclock.c in the daemon code.

You can also use tickadj -a to set tickadj in the running kernel.
In addition, tickadj -A will compute the value to set based on the
kernel's value of tick, while the -t flag allows one to set the
value of tick and the -s flag will set the value of dosynctodr
to zero.  This is an alternative for people who can't change the
values in the kernel's disk image.

In addition, the -p flag will set the noprintf variable. This will
suppress any kernel messages. Kernel message can then only be seen via
syslog(3). This inhibits clockhopping due to kernel printf's.

