Date: Sun, 11 Feb 1996 17:25:58 +0100 From: Poul-Henning Kamp <phk@critter.tfs.com> To: Bruce Evans <bde@zeta.org.au> Cc: current@freebsd.org Subject: Re: calibrating clocks Message-ID: <6665.824055958@critter.tfs.com> In-Reply-To: Your message of "Mon, 12 Feb 1996 01:43:56 %2B1100." <199602111443.BAA13304@godzilla.zeta.org.au>
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> >You know about the counter in the APIC too ? > > >It runs at the "bus frequency" but that may vary as well :-( > > No. What's an APIC? I found the description of the counter, pretty damn useless for our purposes I presume, since the bus-clock can be tweaked for power-mgt. There is support for one-shot and periodic mode. IRQ on zero count. It runs of the bus-clock (60/66MHz) there is a prescaler taking 1,2,4,8, 16,32,64 or 128. The counter itself is 32bit, and it's memory-mapped. There is a R/W Initial count register and a R/O Current count register. If IC is 'N' then the CC runs N, N-1, N-2 ... 2, 1, N, N-1 in periodic mode. CC is loaded from IC when you write to IC. There is also an erratum that says that they got it wrong the first time around, nothing major, just the zero-tick being being the width of the input (bus ?) clock rather than zero. -- Poul-Henning Kamp | phk@FreeBSD.ORG FreeBSD Core-team. http://www.freebsd.org/~phk | phk@login.dknet.dk Private mailbox. whois: [PHK] | phk@ref.tfs.com TRW Financial Systems, Inc . Future will arrive by its own means, progress not so.
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