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From devnull@lkml.org Fri Apr 26 21:05:15 2024 Delivery-date: Mon, 10 Apr 2006 14:18:44 +0200 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751156AbWDJMSS (ORCPT ); Mon, 10 Apr 2006 08:18:18 -0400 Received: from spirit.analogic.com ([204.178.40.4]:58125 "EHLO spirit.analogic.com") by vger.kernel.org with ESMTP id S1751155AbWDJMSR convert rfc822-to-8bit (ORCPT ); Mon, 10 Apr 2006 08:18:17 -0400 Received: from chaos.analogic.com ([10.112.50.11]) by phoenix.analogic.com with Microsoft SMTPSVC(6.0.3790.211); Mon, 10 Apr 2006 08:18:02 -0400 Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT X-MimeOLE: Produced By Microsoft Exchange V6.5.7226.0 Received: from chaos.analogic.com (localhost [127.0.0.1]) by chaos.analogic.com (8.12.11/8.12.11) with ESMTP id k3ACI20n025597; Mon, 10 Apr 2006 08:18:02 -0400 Received: (from linux-os@localhost) by chaos.analogic.com (8.12.11/8.12.11/Submit) id k3ACI1Y0025596; Mon, 10 Apr 2006 08:18:02 -0400 In-Reply-To: <200604080917.39562.ak@suse.de> X-OriginalArrivalTime: 10 Apr 2006 12:18:02.0775 (UTC) FILETIME=[D065BA70:01C65C98] content-class: urn:content-classes:message Subject: Re: Black box flight recorder for Linux Date: Mon, 10 Apr 2006 08:18:01 -0400 Message-Id: X-MS-Has-Attach: X-MS-TNEF-Correlator: Thread-Topic: Black box flight recorder for Linux Thread-Index: AcZcmNBv0N2qS7ToRKKgXDIfnxodxg== References: <5ZjEd-4ym-37@gated-at.bofh.it> <5ZlZk-7VF-13@gated-at.bofh.it> <4437C335.30107@shaw.ca> <200604080917.39562.ak@suse.de> From: "linux-os \(Dick Johnson\)" To: "Andi Kleen" Cc: "Robert Hancock" , "linux-kernel" Reply-To: "linux-os \(Dick Johnson\)" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 8 Apr 2006, Andi Kleen wrote: > On Saturday 08 April 2006 16:05, Robert Hancock wrote: >> Andi Kleen wrote: >>> James Courtier-Dutton writes: >>>> Now, the question I have is, if I write values to RAM, do any of those >>>> values survive a reset? >>> >>> They don't generally. >>> >>> Some people used to write the oopses into video memory, but that >>> is not portable. >> >> I wouldn't think most BIOSes these days would bother to clear system RAM >> on a reboot. Certainly Microsoft was encouraging vendors not to do this >> because it slowed down system boot time.to > > Reset button is like a cold boot and it generally ends up with cleared > RAM. > > -Andi Further, in a boot where the BIOS needs to initialize hardware, It will write all RAM before enabling NMI. This makes sure that the parity bit(s) are set properly. Most BIOS will attempt to preserve RAM on a 'warm' boot as a throw-back to the '286 days with their above-1MB-memory-manager paged RAM because the only way to get back from protected mode to 16-bit real mode was a hardware reset. When using a memory-manager like DOS's HIMEM.SYS, you might actually be rebooting the machine hundreds of times per second! If you want to make a flight-data recorder, you need to use FAA specs and, as such, you can't rely on second-order effects. You will need write all the parameters to flash (or equivalent) at least 10 times per second. I would advise against putting a file-system on the flash because the file-system might get corrupt because of a bad write during a crash. Instead, I would write a large number of identical groups of parameters (a structure image) at a large number of raw offsets, each with the required time-stamp. This, done the required 10 times per second. Note that the NTSB, in investigating some light airplane accidents, has been successful extracting data from hand-held GPS receivers and FADEC controllers, so using flash RAM for accident investigation has some successful history (useful for obtaining certification). I once proposed a FDR for light aircraft that would cost the end-user under $2,000. This was to use a small embedded CPU, raw NAV inputs from the panel, a cheap accelerometer, and some pressure sensors for altimetry. This would be mounted in the tail, requiring no user (pilot) input at all. In the event of a crash, the last hour of flight could be retrieved. Typical response; "There is no market for this...." Good luck! Cheers, Dick Johnson Penguin : Linux version 2.6.15.4 on an i686 machine (5589.42 BogoMips). Warning : 98.36% of all statistics are fiction, book release in April. _  **************************************************************** The information transmitted in this message is confidential and may be privileged. Any review, retransmission, dissemination, or other use of this information by persons or entities other than the intended recipient is prohibited. If you are not the intended recipient, please notify Analogic Corporation immediately - by replying to this message or by sending an email to DeliveryErrors@analogic.com - and destroy all copies of this information, including any attachments, without reading or disclosing them. 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