From owner-cvs-all  Tue Sep 17  6:36:58 2002
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Date: Tue, 17 Sep 2002 23:44:50 +1000 (EST)
From: Bruce Evans <bde@zeta.org.au>
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To: Don Lewis <dl-freebsd@catspoiler.org>
Cc: brandt@fokus.gmd.de, <phk@critter.freebsd.dk>,
	<archie@dellroad.org>, <joe@FreeBSD.org>, <obrien@FreeBSD.org>,
	<cvs-committers@FreeBSD.org>, <cvs-all@FreeBSD.org>
Subject: Re: cvs commit: src/sys/kern kern_timeout.c 
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On Tue, 17 Sep 2002, Don Lewis wrote:

> On 17 Sep, Harti Brandt wrote:
> ....
> > (1) replaced all calls to DELAY(1) with a bus_space_read_4() on a card
> > address. Because there are 184 DELAY(1) calls in each xl_mii_readreg each
> > of which takes a mean of 8.5usecs this cuts down the overall time from
> > 1.8msec to around 320usecs.
>
> I think we're probably ok here.  The standard says the minimum high and
> low times for the clock signal are 160ns, with a minimum clock period of
> 400ns.  If I do the math correctly, your scheme wiggles something about
> every 1.7us.

Maybe the total time can be reduced a lot more by using the minimum delays
specified by the standard (using nanodelay(9unimplemented)).  You would
find out if there is hardware that doesn't comply with the standard :-).

Bruce


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