From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 12877 invoked by alias); 30 May 2006 09:25:22 -0000 Received: (qmail 12379 invoked by uid 22791); 30 May 2006 09:25:21 -0000 X-Spam-Check-By: sourceware.org Received: from smtp1.iitb.ac.in (HELO smtp1.iitb.ac.in) (202.68.145.249) by sourceware.org (qpsmtpd/0.31) with SMTP; Tue, 30 May 2006 09:25:16 +0000 Received: (qmail 17072 invoked from network); 30 May 2006 14:39:28 +0530 Received: from unknown (HELO ldns1.iitb.ac.in) (10.200.12.1) by smtp1.iitb.ac.in with SMTP; 30 May 2006 14:39:28 +0530 Received: (qmail 20038 invoked by uid 509); 30 May 2006 09:09:28 -0000 Received: from 10.105.1.1 by ldns1 (envelope-from , uid 501) with qmail-scanner-1.25 (clamdscan: 0.88/1499. spamassassin: 3.1.0. Clear:RC:1(10.105.1.1):. Processed in 0.030129 secs); 30 May 2006 09:09:28 -0000 Received: from unknown (HELO cse.iitb.ac.in) (10.105.1.1) by ldns1.iitb.ac.in with SMTP; 30 May 2006 09:09:27 -0000 Received: (qmail 10717 invoked by uid 11940); 30 May 2006 09:15:31 -0000 Received: from 10.105.1.11 by jeeves.cse.iitb.ac.in (envelope-from , uid 11926) with qmail-scanner-1.25 (clamdscan: 0.87/1499. spamassassin: 3.1.0. Clear:RC:1(10.105.1.11):. Processed in 0.026717 secs); 30 May 2006 09:15:31 -0000 Received: from mars.cse.iitb.ac.in ([10.105.1.11]) (envelope-sender ) by cse.iitb.ac.in (qmail-ldap-1.03) with SMTP for ; 30 May 2006 09:15:31 -0000 Date: Tue, 30 May 2006 09:25:00 -0000 From: R Vamshi Krishna To: Andrew Lunn cc: Fabian Scheler , ecos-discuss@ecos.sourceware.org In-Reply-To: <20060530081637.GH2876@lunn.ch> Message-ID: References: <20060530075335.GG2876@lunn.ch> <69dd805e0605300109k5dcf7986of596c0b5f796c6b4@mail.gmail.com> <20060530081637.GH2876@lunn.ch> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed X-IsSubscribed: yes Mailing-List: contact ecos-discuss-help@ecos.sourceware.org; run by ezmlm Precedence: bulk List-Subscribe: List-Archive: List-Post: List-Help: , Sender: ecos-discuss-owner@ecos.sourceware.org Subject: Re: [ECOS] Hard-Realtime behaviour X-SW-Source: 2006-05/txt/msg00240.txt.bz2 Continuing on the discussion, doesn't pipelining on modern processors add to our woes. Because then we cannot really determine if a particular instruction is going to 'x' cycles or 'y' cycles. eCos does support disabling instruction and data caches, but is there any way that I can disable pipelines in a microprocessor. For example i386ex. @Andrew : As we have seen most of what is necessary for hard realtime behaviour of eCos already is implemented. Can you help me in figuring out what is it that is missing that makes eCos soft real-time. On Tue, 30 May 2006, Andrew Lunn wrote: > On Tue, May 30, 2006 at 10:09:21AM +0200, Fabian Scheler wrote: >>> Disable the caches. How long something takes to execute will depend on >>> what is in the cache. If the code to be executed is still in the cache >>> from the last time it was executied, it will execute a lot quicker >>> than if it has to be fetches from RAM/ROM. The same applies to the >>> data to be processed. So to be deterministic, you need to disable >>> caches. >> >> In order to guarantee deadlines, the worst case has to be >> deterministic, not the average case! In event-driven systems >> everything should be fine as long as your worst case response time is >> beneath your deadline, things get problematic when you use >> time-discrete algorithms, of course, but in this case you are better >> of using a time-driven approach, anyway. > > So you at least need to disable caches when you determine what the > worst case is, assuming the cache is actually helping you. > > Andrew > > > -- Regards, Vamshi ------------------------------------------------- R.Vamshi Krishna, M.Tech. CSE (II year), IIT Bombay Room no. 320, A-wing, Hostel-12 Mobile : +919869781633 ------------------------------------------------- Yesterday is a past, tomorrow is a future , today is a gift that's why it's called 'present' -- Before posting, please read the FAQ: http://ecos.sourceware.org/fom/ecos and search the list archive: http://ecos.sourceware.org/ml/ecos-discuss