From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750722AbWFQREO (ORCPT ); Sat, 17 Jun 2006 13:04:14 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750723AbWFQREO (ORCPT ); Sat, 17 Jun 2006 13:04:14 -0400 Received: from smtp.osdl.org ([65.172.181.4]:15596 "EHLO smtp.osdl.org") by vger.kernel.org with ESMTP id S1750722AbWFQREO (ORCPT ); Sat, 17 Jun 2006 13:04:14 -0400 Date: Sat, 17 Jun 2006 10:04:07 -0700 From: Andrew Morton To: john stultz Cc: zippel@linux-m68k.org, linux-kernel@vger.kernel.org Subject: Re: clocksource Message-Id: <20060617100407.3596be29.akpm@osdl.org> In-Reply-To: <1150428084.15267.74.camel@cog.beaverton.ibm.com> References: <20060604135011.decdc7c9.akpm@osdl.org> <1149538810.9226.29.camel@localhost.localdomain> <1149622955.4266.84.camel@cog.beaverton.ibm.com> <1149753904.2764.24.camel@leatherman> <1150428084.15267.74.camel@cog.beaverton.ibm.com> X-Mailer: Sylpheed version 2.2.4 (GTK+ 2.8.17; i686-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 15 Jun 2006 20:21:24 -0700 john stultz wrote: > The method I came up with is really just P-D (proportional-derivative) > control, but that should be ok since the adjustments are all linear so I > don't think the integral control is necessary (control theorists can > pipe in here). Boy, that takes me back. If you don't feed back the integral you'll end up with an output which has a steady-state offset error against the control point (unless the forward gain is infinite, and it never is). I don't know if that matters here, but it cannot be good. If you feed back the integral of the error then it introduces the possibility of instability. Probably in this application you can just overdamp the thing to avoid that. It'll make it slower to respond to changes in the setpoint.