Date: Tue, 25 Jul 2006 20:26:54 +0000 From: "Poul-Henning Kamp" <phk@phk.freebsd.dk> To: David Malone <dwmalone@maths.tcd.ie> Cc: src-committers@FreeBSD.org, cvs-src@FreeBSD.org, "Christian S.J. Peron" <csjp@FreeBSD.org>, cvs-all@FreeBSD.org, Sam Leffler <sam@errno.com>, Jung-uk Kim <jkim@FreeBSD.org> Subject: Re: cvs commit: src/sys/net bpf.c Message-ID: <11936.1153859214@critter.freebsd.dk> In-Reply-To: Your message of "Tue, 25 Jul 2006 21:23:11 %2B0100." <200607252123.aa75409@salmon.maths.tcd.ie>
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In message <200607252123.aa75409@salmon.maths.tcd.ie>, David Malone writes: >> I'm not sure I know what you mean by "trivial timecounter", but the >> only reason we don't have a way to deregister a timecounter yet is >> that so far I'm probably the only one who have ever need it :-) > >I was thinking about this recently too actually, as I was going to >see how good the 64 bit counter on ath cards was in comparison to >other things that were available. The first gottcha to look out for is upper/lower half rollover issues, if you read it as two 32 bit registers: you need to check if the lower part rolled over without the upper part getting updated, or the more pathological case: the upper part being updated before the lower part rolled voer. 32 bits is quite likely to be enough for a timecounter so that may not even be an issue. Next is the matter of the crystal that drives it, the temperature stability of that xtal etc etc. >other things that were available. I'm not sure how much complexity >a timecounter that could vanish at any moment would introduce - I >didn't get that far yet. It's not too bad, we can switch pretty quickly. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 phk@FreeBSD.ORG | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence.
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