readme

内核中关于nano计时的功能

See the ./html/index.htm for run-time documentation

A "make" with just about any dirty rottten C compiler will bake the test
and demonstration program. The program is not intended to do anything other
than verify the impulse response of the clock discipline loop and look for
glitches.

The routines are designed to be implemented in the kernels of generic
operating systems in a reasonably portable way, although the definition
of portable here is rather loose. Comments are liberally sprinkled in
the sources and should give guidance where the code fragments go. There
are two principle routines, ktime.c and micro.c. The ktime.c routine is
is to be integrated with usual Unix suspect kern_clock.c or whaterver name
this function has been morphed to.  This routine handles timer interrupts,
increments the clock tick and handles the second overflow. The micro.c
routine interpolates between timer interrupts in order to provide nanosecond
resolution.

These routines have been integrated in stock kernels for FreeBSD and is an
available add-on for Linux. An earlier version is in the stock kernels
for Digital Alpha (or whatever name that has morphed to), and Solaris. The
header files and some code fragments are in the alpha, freebsd, solaris and
sunos directories in this distribution.

The pulse-per-second (PPS) interface support is also in this distribution,
although in fragmentary form. It is available in stock kernels for Solaris
and FreeBSD and is an available add-on for Linux. Although it has been
implemented for Alpha and SunOS, it never made it to the stock kernels.

The tprotime.c and tpro.h are for SunOS SBus machines, which are rather rare
these days. The TPRO board is a precision oscillator/counter synchronized
to an IRIG signal. Once upon a time the SunOS kernel was modified to use
it as the system clock, which provided truly awesome performance. It is
included here by way of historic reminder.

Dave Mills
23 September 2002