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about time

    Date: Thu, 08 Mar 90 12:02:14 EST
    From: bouma@cs.purdue.edu

	I have read with interest the articles about reseting network time
	as we have the same situation Steve Nicoud is experiencing. But none
	has answered the main question of how to figure out which machine is
	supplying the bogus time. #'net-print-host-times just prints the times
	on the lisp machines. What would help (me) a great deal is simply an
	explanation of how the machine figures out what time it is when it is
	booted. Doesn't the internal calendar clock keep running even when in
	the fep? Then why always go to the network to get the (wrong) time when
	booted? Can I at least isolate the problem to one of the machines in our
	namespace? As always, any help is greatly appreciated.

I wondered if someone was going to ask this question.  Things have changed a
bit for 8.0, so I will try to explain the new and old schemes.

When booting at a standalone site (Standalone attribute of the site object
says "Yes") the battery backed hardware calendar clock will be used.  When
booting a MacIvory or UX400S, the clock from the Mac or Sun will always be
used, whether the site is standalone or not.  But a MacIvory or UX400S is
permitted to answer requests for the time on the network.  So, it is possible
for a MacIvory or a UX400S to propagate bad times if their respective hosts
have bad times.

When booting at a non-standalone site with a non-embedded system, a broadcast
will be made on the primary network (Chaos only for pre-8.0) for the time of
day.  Since the primary network can only be chaos before 8.0, only lispms will
respond.  The responses to the broadcast are collected and the median time is
chosen for the status line time.  If the broadcast fails to get any responses,
pre-8.0 machines would give you a nasty prompt in the cold-load asking you to
type the time.  In 8.0, this has been changed so the calendar clock will be
used when the broadcast failed.  The only time you should receive a prompt for
the time is when the calendar clock is broken or uninitialized.  After the
machine is booted the time is kept by the software.

So, the hardware calendar clock is only used at boot time and then only for
standalone sites, unless no one responds to the time broadcast.