From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261400AbVGLMzE (ORCPT ); Tue, 12 Jul 2005 08:55:04 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261414AbVGLMzD (ORCPT ); Tue, 12 Jul 2005 08:55:03 -0400 Received: from mail22.syd.optusnet.com.au ([211.29.133.160]:8356 "EHLO mail22.syd.optusnet.com.au") by vger.kernel.org with ESMTP id S261400AbVGLMyP (ORCPT ); Tue, 12 Jul 2005 08:54:15 -0400 From: Con Kolivas To: linux-kernel@vger.kernel.org Subject: Re: [PATCH] i386: Selectable Frequency of the Timer Interrupt Date: Tue, 12 Jul 2005 22:52:59 +1000 User-Agent: KMail/1.8.1 Cc: Vojtech Pavlik , George Anzinger , "Martin J. Bligh" , Lee Revell , Diego Calleja , azarah@nosferatu.za.org, akpm@osdl.org, cw@f00f.org, torvalds@osdl.org, christoph@lameter.org References: <200506231828.j5NISlCe020350@hera.kernel.org> <20050712121008.GA7804@ucw.cz> <200507122239.03559.kernel@kolivas.org> In-Reply-To: <200507122239.03559.kernel@kolivas.org> MIME-Version: 1.0 Content-Type: multipart/signed; boundary="nextPart2532963.n1RfQfmQy4"; protocol="application/pgp-signature"; micalg=pgp-sha1 Content-Transfer-Encoding: 7bit Message-Id: <200507122253.03212.kernel@kolivas.org> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org --nextPart2532963.n1RfQfmQy4 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline On Tue, 12 Jul 2005 22:39, Con Kolivas wrote: > On Tue, 12 Jul 2005 22:10, Vojtech Pavlik wrote: > > The PIT crystal runs at 14.3181818 MHz (CGA dotclock, found on ISA, ...) > > and is divided by 12 to get PIT tick rate > > > > 14.3181818 MHz / 12 = 1193182 Hz > > > > The reality is that the crystal is usually off by 50-100 ppm from the > > standard value, depending on temperature. > > > > HZ ticks/jiffie 1 second error (ppm) > > --------------------------------------------------- > > 100 11932 1.000015238 15.2 > > 200 5966 1.000015238 15.2 > > 250 4773 1.000057143 57.1 > > 300 3977 0.999931429 -68.6 > > 333 3583 0.999964114 -35.9 > > 500 2386 0.999847619 -152.4 > > 1000 1193 0.999847619 -152.4 > > > > Some HZ values indeed fit the tick frequency better than others, up to > > 333 the error is lost in the physical error of the crystal, for 500 and > > 1000, it definitely is larger, and thus noticeable. > > > > Some (less round and nice) values of HZ would fit even better: > > > > HZ ticks/jiffie 1 second error (ppm) > > --------------------------------------------------- > > 82 14551 1.000000152 0.2 > > Most interesting... Would 838 Hz be a much better choice than 1000 then? > (apart from the ugliness). Duh I should have looked lower where you suggested 864, sorry. 864 1381 1.000001829 1.8 Cheers, Con --nextPart2532963.n1RfQfmQy4 Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.1 (GNU/Linux) iD8DBQBC070vZUg7+tp6mRURAimYAKCEPUPXGHkn/2Nd5S0wxdS9UC0PwACeKsdv eUI5aa/VDsGbvMdICKF6LTc= =QjFM -----END PGP SIGNATURE----- --nextPart2532963.n1RfQfmQy4--