From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261514AbVFMMD4 (ORCPT ); Mon, 13 Jun 2005 08:03:56 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261520AbVFMMD4 (ORCPT ); Mon, 13 Jun 2005 08:03:56 -0400 Received: from [195.23.16.24] ([195.23.16.24]:9181 "EHLO bipbip.comserver-pie.com") by vger.kernel.org with ESMTP id S261514AbVFMMDv (ORCPT ); Mon, 13 Jun 2005 08:03:51 -0400 Message-ID: <42AD761C.6060709@grupopie.com> Date: Mon, 13 Jun 2005 13:03:40 +0100 From: Paulo Marques Organization: Grupo PIE User-Agent: Mozilla Thunderbird 1.0 (X11/20041206) X-Accept-Language: en-us, en MIME-Version: 1.0 To: Gene Heskett Cc: linux-kernel@vger.kernel.org Subject: Re: [PATCH] local_irq_disable removal References: <1118533485.13312.91.camel@tglx.tec.linutronix.de> <1118534993.5593.175.camel@sdietrich-xp.vilm.net> <200506112105.11067.gene.heskett@verizon.net> In-Reply-To: <200506112105.11067.gene.heskett@verizon.net> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Gene Heskett wrote: > [...] > Lets add the operation of 4 or more stepper motors in real time for > smaller milling machines. There, the constraints are more related to > maintaining a steady flow of step/direction data at high enough > speeds to make a stepper, with 8 microsteps per step, and 240 steps > per revolution, run smoothly at speeds up to say 20 kilohertz, or 50 > microseconds per step, maintaining that 50 microseconds plus or minus > not more than 5 microseconds else the motors will start sounding > ragged and stuttering. This is the kind of problem that is screaming "give me dedicated hardware!". Why would one spend $500+ on a PC to do the work of a $2 microcontroller (and possibly throw in an FPGA to the mix)?. Not to mention that the microcontroller/FPGA would maintain 50us +/- 0us instead of the 50 +/- 5 you've mentioned. The same goes for the "hand under the saw". A simple transistor/triac/whatever and a logic circuit would stop the saw, we don't need any real time OS for that (and I would certainly trust the logic circuit more than any real time OS :). IMHO, the kind of problems where real time OS's are useful are the kind that require computational power while having real-time constraints. Like the sound effects processor for the guitar that Lee Revell already mentioned or controlling an airplane in flight that has to measure a lot of sensors, do some state space calculations with some not-so-small matrices (together with Kalman filtering, etc.) and move the actuators. -- Paulo Marques - www.grupopie.com An expert is a person who has made all the mistakes that can be made in a very narrow field. Niels Bohr (1885 - 1962)