I have updated design.tar.gz, a document with patches and example
programs that deal with the Linux kernel clock support for NTP,
especially with PPS (pulse per second) support. The last kernel I
tried to patch was 2.0.28.
The file can be found in /pub/wiu09524/PPS on
pcphy4.physik.uni-regensburg.de.
The update mainly contains two new utility programs: One uses the RTC
driver to generate a PPS pulse with software (poor man's frequency
generator), the other one enables PPS detection on a serial port and
monitors some related kernel time variables.
For xntpd 3.5.89 you still had to "enable pps" manually to make the
thing work. Of course if you have a precision PPS source, don't use
the software solution; it's just a debugging aid!
Ulrich
P.S. The patch is experimental, but I did never have a problem. I
also did not get any complaints (except those on programming)