From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Tue, 28 Aug 2001 15:45:18 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Tue, 28 Aug 2001 15:44:59 -0400 Received: from h157s242a129n47.user.nortelnetworks.com ([47.129.242.157]:20670 "EHLO zcars0m9.ca.nortel.com") by vger.kernel.org with ESMTP id ; Tue, 28 Aug 2001 15:44:53 -0400 Message-ID: <3B865DCB.C60525B@nortelnetworks.com> Date: Fri, 24 Aug 2001 09:59:39 -0400 X-Sybari-Space: 00000000 00000000 00000000 From: "Christopher Friesen" X-Mailer: Mozilla 4.77 [en] (X11; U; Linux 2.4.3-custom i686) X-Accept-Language: en MIME-Version: 1.0 To: Gabriel Paubert Cc: linux-kernel Subject: Re: [PATCH] (comments requested) adding finer-grained timing to PPC add_timer_randomness() In-Reply-To: Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-Orig: Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Gabriel Paubert wrote: > No, both the RTC and the decrementer count nanoseconds, except that the 7 > LSB are not implemented because the timebase clock should have a period of > 128 ns (7.8125 MHz, but according to Takashi Oe, many 601 systems did not > bother to provide the exact frequency and are off by 11 parts in 4096 or > so). As such the LSB can't be used to estimate randomness and the value > must be shifted right by 7. So you need some conditional code (or boot > time patching). At this point you can throw in the high order part > (RTCU/TBU) for additional randomization (RTCU changes much faster on 601, > once per second, than on the other processors). Have you got any links to information on boot time patching? -- Chris Friesen | MailStop: 043/33/F10 Nortel Networks | work: (613) 765-0557 3500 Carling Avenue | fax: (613) 765-2986 Nepean, ON K2H 8E9 Canada | email: cfriesen@nortelnetworks.com