Date: Tue, 17 Sep 2002 23:44:50 +1000 (EST) From: Bruce Evans <bde@zeta.org.au> 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 Message-ID: <20020917233828.H11067-100000@gamplex.bde.org> In-Reply-To: <200209170908.g8H98Hwr015356@gw.catspoiler.org>
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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 To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe cvs-all" in the body of the message
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