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diff --git a/contrib/ntp/html/kern.htm b/contrib/ntp/html/kern.htm new file mode 100644 index 0000000..b1ee383 --- /dev/null +++ b/contrib/ntp/html/kern.htm @@ -0,0 +1,51 @@ +<HTML><HEAD><TITLE> +A Kernel Model for Precision Timekeeping +</TITLE></HEAD><BODY><H3> +A Kernel Model for Precision Timekeeping +</H3><HR> + +<P>The technical memorandum: <I>A Kernel Model for Precision +Timekeeping</I><A +HREF="http://www.eecis.udel.edu/~mills/database/memos/memo96b.ps"> +(PostScript) </A>describes an engineering model which implements a +precision time-of-day function for a generic operating system. The model +is based on the principles of disciplined oscillators using phase-lock +loops (PLL) and frequency-lock loops (FLL) often found in the +engineering literature. The model uses a hybrid PLL/FLL discipline +algorithm implemented in the kernel. The hybrid loop provides automatic +time and frequency steering with update intervals from a few seconds to +over one day. + +<P>The hybrid PLL/FLL has been implemented in the Unix kernels for +several workstations, including those made by Sun Microsystems, Digital +and Hewlett Packard. Currently, the modifications are in licensed +kernels for Digital Unix 4.0 and Sun Solaris 2.6. Since these specific +implementations involve modifications to licensed code, they cannot be +provided directly. Inquiries should be directed to the manufacturer's +representatives. In addition to the licensed kernels, the hybrid PLL/FLL +has been implemented in the nonlicensed kernels for Linux and FreeBSD. +The engineering model for these implementations, including a simulator +with code segments almost identical to the implementations, but not +involving licensed code, is available via the web at <A +HREF="http://www.eecis.udel.edu/~mills/ntp/ntp">kernel.tar.Z</A> or by +anonymous FTP from ftp.udel.edu in the <TT>pub/ntp</TT> directory. + +<P>The model changes the way the system clock is adjusted in time and +frequency, as well as provides mechanisms to discipline its time and +frequency to an external precision timing source, such as a pulse-per- +second (PPS) signal. The model incorporates a generic system-call +interface for use with the Network Time Protocol (NTP) or similar time +synchronization protocol. The NTP software daemons for Version 3 +<TT>xntpd</TT> and Version 4 <TT>ntpd</TT> operate with this model +to provide synchronization limited in principle only by the accuracy and +stability of the external timing source. There are two new system calls +defined in the model, <TT>ntp_gettime()</TT>, which returns a structure +including the current time, estimated error and maximum error, and +<TT>ntp_adjtime()</TT>, which provides a means to adjust kernel +variables, including the current time and frequency offsets. Further +information on the calling sequences and variable definitions are in the +<TT>/usr/include/sys/timex.h</TT> file. + +<hr><a href=index.htm><img align=left src=pic/home.gif></a><address><a +href=mailto:mills@udel.edu> David L. Mills <mills@udel.edu></a> +</address></a></body></html> |
