From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 8025 invoked by alias); 6 Jun 2007 09:51:46 -0000 Received: (qmail 7952 invoked by uid 22791); 6 Jun 2007 09:51:45 -0000 X-Spam-Check-By: sourceware.org Received: from ug-out-1314.google.com (HELO ug-out-1314.google.com) (66.249.92.174) by sourceware.org (qpsmtpd/0.31) with ESMTP; Wed, 06 Jun 2007 09:51:38 +0000 Received: by ug-out-1314.google.com with SMTP id g33so418848ugd for ; Wed, 06 Jun 2007 02:51:35 -0700 (PDT) Received: by 10.82.112.16 with SMTP id k16mr612969buc.1181123495511; Wed, 06 Jun 2007 02:51:35 -0700 (PDT) Received: by 10.82.127.9 with HTTP; Wed, 6 Jun 2007 02:51:35 -0700 (PDT) Message-ID: <4690b0d10706060251nfb2c3a0o4f681317413e9616@mail.gmail.com> Date: Wed, 06 Jun 2007 10:37:00 -0000 From: "M Arshad Khan" To: "M Arshad Khan" , ecos-discuss@ecos.sourceware.org, ecos-discuss@sources.redhat.com In-Reply-To: <20070605123137.GA12951@lunn.ch> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <4690b0d10706042159k40c3e12cp7e92a4a4cb66d2b0@mail.gmail.com> <20070605123137.GA12951@lunn.ch> Mailing-List: contact ecos-discuss-help@ecos.sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: ecos-discuss-owner@ecos.sourceware.org Subject: Re: [ECOS] Drift in Real Time Clock X-SW-Source: 2007-06/txt/msg00064.txt.bz2 Message-ID: <20070606103700.2kvfO8zfd27aZv-pXjbc1iSOMDegsT3y7qkVN4pbKA0@z> On 6/5/07, Andrew Lunn wrote: > On Tue, Jun 05, 2007 at 09:59:21AM +0500, M Arshad Khan wrote: > > Hello > > we r running eCos on simple intel based PC. we want to find the drift > > in the real time colck, for this we simply capture a 100Sec signal > > using 20mSec interrupt. the signal was captured using a counter by > > triggering the channel of the counter using parallel port of the PC. > > the code is given below. > > from the results we found that the drift was 7mili Sec in 100 Sec. > > This drift is very large to fitt for real time colck. we also tried > > this code on different PC's but app same results. can any body tell me > > why i am getting so much drift... > > any suggestions.. > > > > I believe the PC clock ticks at a base rate of 1193182Hz. The eCos > clock is usually configured for 10ms. That would be 11931.82 > ticks. Obviously you cannot have fractional ticks, so you end up with > 11932 ticks per 10ms. The error is then 0.0015%. > > 0.0015% of 100Sec = 0.0015seconds i.e. 1.5ms. So something is not > right somewhere, but i think you get the idea. > > Check i have the clock frequency correct and perform your own > calculation about what accuracy is achievable. > > Andrew > yes the problem was with the initialization value i varry this value and got delay of 1.5ms in 100 s using initialization value of 11934 (very strange...). now i want to reduce the time of one tick from 10ms to 1ms... so that i can generate interrupt of 1ms i tried it by changing the values of clock resolution numerator and clock resolution denominator but same 10ms. any suggestion in this regard?... -- Before posting, please read the FAQ: http://ecos.sourceware.org/fom/ecos and search the list archive: http://ecos.sourceware.org/ml/ecos-discuss