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From: jeffrey@masscomp.UUCP (Jeff Jones)
Newsgroups: comp.unix.questions,comp.unix.wizards
Subject: Delay with no real time clock
Message-ID: <2414@masscomp.UUCP>
Date: Wed, 14-Oct-87 19:18:42 EDT
Article-I.D.: masscomp.2414
Posted: Wed Oct 14 19:18:42 1987
Date-Received: Sat, 17-Oct-87 16:50:40 EDT
Reply-To: jeffrey@masscomp.UUCP (Jeff Jones)
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Organization: MASSCOMP - Westford, Ma
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Xref: mnetor comp.unix.questions:4534 comp.unix.wizards:4937

I am working with a driver that must wait for a specified period of
time (usually less than one second) after issuing a command before
assuming that a device is not present.  This must happend during
device initialization time.

There are no real time clock interrupts during the device initialization
phase of our kernel.  The system time counter (lbolt in our case) does
not get incremented HZ times per second until after all devices
are initialized.  So, 

	How do you determine how much time has expired
	when you have no real time clock interrupt?

One would suppose the answer would be to set up a loop with a specific
number of instructions and then have some macro that tells you how
many of these loops occur per second.  But that would entail changing
the macro everytime you change the clock rate of the processor
(or changing the contents of the loop).  This is also somewhat
non-deterministic due the fact that the loop may or may not be in
an instruction cache.

I am curious to find our how others have dealt with this problem.

Thanx,
jeff jones