From owner-freebsd-questions Fri May 9 13:02:09 1997 Return-Path: Received: (from root@localhost) by hub.freebsd.org (8.8.5/8.8.5) id NAA25943 for questions-outgoing; Fri, 9 May 1997 13:02:09 -0700 (PDT) Received: from dyson.iquest.net (dyson.iquest.net [198.70.144.127]) by hub.freebsd.org (8.8.5/8.8.5) with ESMTP id NAA25937 for ; Fri, 9 May 1997 13:01:51 -0700 (PDT) Received: (from root@localhost) by dyson.iquest.net (8.8.5/8.6.9) id OAA00252; Fri, 9 May 1997 14:59:47 -0500 (EST) From: "John S. Dyson" Message-Id: <199705091959.OAA00252@dyson.iquest.net> Subject: Re: catching a powerfail NMI In-Reply-To: from Stephen Roome at "May 9, 97 08:02:03 pm" To: steve@visint.co.uk (Stephen Roome) Date: Fri, 9 May 1997 14:59:46 -0500 (EST) Cc: freebsd-questions@FreeBSD.ORG Reply-To: dyson@FreeBSD.ORG X-Mailer: ELM [version 2.4ME+ PL31 (25)] MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-questions@FreeBSD.ORG X-Loop: FreeBSD.org Precedence: bulk > > (This is serious) > > I'm looking at the possibilty of using the powerfail NMI > which seems to already have some code for it in > /sys/i386/i386/trap.c > > Basically, with a bunch of capacitors and a monostable we think we can > make a very cheap UPS, which gives long enough to get the system to do > little more than just fasthalt or somesuch. :-). 1 Farad == 1V drop per amp every second. Say that you have .5 Farads (500 000 Microfarads), and a 15 Amp load, then you will have 1/30 of a second before you loose a Volt. .5 Farads is a lot of capacitance. (The little low-current supercaps notwithstanding.) I guess that you do have a lot of capacitors!!! John