Date: Tue, 23 Aug 2005 01:06:18 +0200 From: Stefan Bethke <stb@lassitu.de> To: =?ISO-8859-1?Q?S=F8ren_Schmidt?= <sos@freebsd.org> Cc: freebsd-hackers@freebsd.org, m.ehinger@ltur.de Subject: Re: IBM Active Protection System Approach Message-ID: <5051CE43-C8D3-41BD-9944-11EDFEA4300D@lassitu.de> In-Reply-To: <A95A177C-8C1B-47F6-8344-B818F6A97EAF@FreeBSD.org> References: <OF828DE8D9.036E29C8-ONC1257065.002A679F-C1257065.002CBB28@gateway-inter.net> <A95A177C-8C1B-47F6-8344-B818F6A97EAF@FreeBSD.org>
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Am 22.08.2005 um 17:26 schrieb S=F8ren Schmidt: > On 22/08/2005, at 10:08, m.ehinger@ltur.de wrote: >> what would be the best approach to implement aps on FreeBSD? >> >> I got an Accelerometer driver which will deliver data. First =20 >> Version is available at >> https://sourceforge.net/project/showfiles.php?=20 >> group_id=3D138242&package_id=3D160977 >> >> We have to poll the device for information quiet often to detect a =20= >> possible shock early enough to park disk drive heads. > Urhm, what type of "accidents" is it we want to protect against here ? > > It will take several tens of mS to get the heads parked if not =20 > hundreds, and the worst case scenario would be that the "accident" =20 > will happen just as the heads are on the way to the parking zone =20 > which would *really* destroy data on there, unless the disk has =20 > special HW to just quickly lift the heads or something. I have no insight into either IBM's or Apple's implementation, but =20 I've read that they both rely on detecting the machine being in =20 freefall, or similar acceleration states, as a cue to have the HD =20 park the heads before a possible impact. Early reports from Mac enthusiast sites (and I believe similar =20 reports from IBM users) indicate that the hysteresis is so small that =20= gently pounding the table the notebook is sitting on will make the =20 drive park the heads, and lead to 10 to 20 seconds delay before the =20 drive can be accessed again. Given how tightly coupled mechanically the HD in most notebooks is to =20= it's shell, it seems a very good idea to pursue. If you have access to a new(ish) PowerBook, I recommend checking out =20 http://www.kernelthread.com/software/ams/. The sensitivity of the =20 accelerometer is truely astounding. (For those who haven't seen it: =20 you turn the notebook, and the demo window is turned so it stays =20 level. It takes *really* small movements to confuse the system.) Stefan --=20 Stefan Bethke <stb@lassitu.de> Fon +49 170 346 0140
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