[time-nuts] FreeBSD, NetBSD, or Minix-III?

[M. Warner Losh]

In message: <20090519095316.1e1f4b46.attila at kinali.ch>
            Attila Kinali <attila at kinali.ch> writes:
: On Sat, 16 May 2009 15:09:07 +0000
: "Poul-Henning Kamp" <phk at phk.freebsd.dk> wrote:
: 
: > In message <4A0EBDEE.2020703 at erols.com>, Chuck Harris writes:
: > 
: > >A "watch" isn't exactly a challenge to an operating system.
: > 
: > Well, no.
: > 
: > But figuring out correct handling of time is a challenge for operating
: > system programmers.
: 
: Out of pure interest: what makes handling of time difficult?
: >From an uneducated point of view it's just updating a counter
: >From an uneducated point of view it's just updating a counter
: in software from a time source in hardware.

Simple, naive time keeping is easy.  Look at all the folks that make
wrist watches.

However, when you are trying to get higher and higher accuracy for the
time, you have to talk to external folks.  Doing this introduces
latency.  There's variation in this latency, and that limits the
synchronization of the times.  Also, there are a number of
environmental factors that affect the quality of the underlying time
keeping hardware since most crystals are sensitive to temperature.

Warner