linux-kernel - Re: [RFC+PATCH] RTC calibration

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Message-ID: <ujrwsux1815.fsf@false.linpro.no>
Date:	Tue, 11 Sep 2007 18:28:06 +0200
From:	Dag-Erling Smørgrav <des@...pro.no>
To:	mgross@...ux.intel.com
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [RFC+PATCH] RTC calibration

Mark Gross <mgross@...ux.intel.com> writes:
> Is it necessary to change the rtc interface?  Can't you detect within
> your m48t59 driver that you are getting consistent time adjustments up
> or down from whats in the rtc and infer it needs speeding up or slowing
> down?

[I didn't notice this when I first replied]

Because of the RTC's low resolution and of how the calibration is
implemented in the chip, you need to sample the clock at intervals of
several hours in order to determine the direction of the required
adjustment.  Repeatedly setting the RTC to the correct time will
actually prevent correct calibration.

DES
-- 
Dag-Erling Smørgrav
Senior Software Developer
Linpro AS - www.linpro.no
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