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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <20070108102501.GA11993@ingate.macqel.be>
Date:	Mon, 8 Jan 2007 11:25:01 +0100
From:	Philippe De Muyter <phdm@...qel.be>
To:	David Brownell <david-b@...bell.net>
Cc:	Linux Kernel list <linux-kernel@...r.kernel.org>,
	Alessandro Zummo <alessandro.zummo@...ertech.it>
Subject: Re: RTC subsystem and fractions of seconds

On Sun, Jan 07, 2007 at 06:10:30PM -0800, David Brownell wrote:

> > One usefull addition for my needs and with a m41t81 is the support of
> > the calibration of the rtc.  However this can perhaps be hidden in the
> > .set_mmss function.
> 
> Doesn't seem like an set_mmss() mechanism at all.  Some drivers give
> sysfs access to an oscillator "trim" mechanism.  What tools do you
> have which track how far off that crystal is?

ntp, either from network or from a radio-clock

and using set_mmss for that purpose seems not so disgusting, because :

- writing to the clock (the expected work of set_mmss) must be disabled when
we observe the clock drift
- set_mmss is always called with a very good precision, so one could
use the time given to set_mmss to compare it to the time given by the RTC
over a long enough period of time (more than 11 minutes) to compute the RTC's
drift and the necessary adjustment.

Of course, if we want something that is not based on ntp, then we may not
overload set_mmss.

Philippe
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/