linux-kernel - Re: RTC subsystem and fractions of seconds

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Message-ID: <20070106232633.GA8535@ingate.macqel.be>
Date:	Sun, 7 Jan 2007 00:26:33 +0100
From:	Philippe De Muyter <phdm@...qel.be>
To:	David Brownell <david-b@...bell.net>
Cc:	Linux Kernel list <linux-kernel@...r.kernel.org>
Subject: Re: RTC subsystem and fractions of seconds

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
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