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From: boykin@custom.UUCP (Joseph Boykin)
Newsgroups: comp.unix.questions,comp.unix.wizards
Subject: Re: Delay with no real time clock
Message-ID: <769@custom.UUCP>
Date: Fri, 16-Oct-87 10:30:05 EDT
Article-I.D.: custom.769
Posted: Fri Oct 16 10:30:05 1987
Date-Received: Sat, 17-Oct-87 23:15:34 EDT
References: <2414@masscomp.UUCP>
Distribution: na
Organization: Custom Software Systems; Natick, MA
Lines: 37
Xref: mnetor comp.unix.questions:4543 comp.unix.wizards:4948

In article <2414@masscomp.UUCP>, jeffrey@masscomp.UUCP (Jeff Jones) writes:
> 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?

There are two solutions which I've used.  One has the advantage
that you don't have to do anything, the other means you might
have to do a little patching after the kernel is built.

1) Since you're doing this at initialization time and hence
not overly concerned about real-time performance, and
since the timeout is relatively short, I would just
wait long enough for your 'best' CPU performance.  If you're
running a 10MHz 68000 vs. a 25MHz 68020 with cache the same code
for the 68K will timeout in, say, 3 seconds instead of 0.5.
Not great, but not a disaster either.

2) Just as you patch the kernel once to change the 'uname' structure
to whatever name you want your system to have, add another location
(or struction) which has whatever other info you might find useful.
I've including things such as clock rate, CPU type, Kernel virtual
offset, plus any other tunable parameters I thought would be
of use.
-- 

Joe Boykin
Custom Software Systems
...necntc!custom!boykin