From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932221AbXAFX0g (ORCPT ); Sat, 6 Jan 2007 18:26:36 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932235AbXAFX0g (ORCPT ); Sat, 6 Jan 2007 18:26:36 -0500 Received: from mail.macqel.be ([194.78.208.39]:18415 "EHLO mail.macqel.be" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932221AbXAFX0f (ORCPT ); Sat, 6 Jan 2007 18:26:35 -0500 Date: Sun, 7 Jan 2007 00:26:33 +0100 From: Philippe De Muyter To: David Brownell Cc: Linux Kernel list Subject: Re: RTC subsystem and fractions of seconds Message-ID: <20070106232633.GA8535@ingate.macqel.be> References: <200701051949.00662.david-b@pacbell.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <200701051949.00662.david-b@pacbell.net> User-Agent: Mutt/1.4.1i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jan 05, 2007 at 07:49:00PM -0800, David Brownell wrote: > > Those rtc's actually have a 1/100th of second > > register. Should the generic rtc interface not support that? > > Are you implying a new userspace API, or just an in-kernel update? My only concern at the moment is initializing linux's timeofday from the rtc quickly and with a good precision. The way it is done currently in drivers/rtc/hctosys.c is 0.5 sec off. We could obtain a much better precision by looping there until the next change (next second for old clocks, next 0.01 second for m41t81, maybe even better for other ones). > > Either way, that raises the question of what other features should > be included. What sub-second precision? Multiple alarms? Ways > to manage output clocks? Sub-HZ periodic alarms? I cannot answer that, but others may have other needs. Philippe --