Mailinglist Archive: opensuse (4547 mails)

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Re: [SLE] realtime clock probs-solved ...
  • From: Anders Johansson <andjoh@xxxxxxxxxx>
  • Date: Tue, 4 May 2004 22:43:06 +0200
  • Message-id: <200405042243.06993.andjoh@xxxxxxxxxx>
On Tuesday 04 May 2004 22.26, Carlos E. R. wrote:
> The Tuesday 2004-05-04 at 21:56 +0200, Anders Johansson wrote:
> > The RTC (real time clock) is on the CMOS chip and powered by its battery,
> > as far as I understand.
>
> Correct.
>
> > Also, from what I can tell, the CMOS clock is accessed
> > quite frequently as part of the timer interrupt.
>
> No, it is not accessed at all, for many reasons. One, it is a very slow
> access. Two, the CPU maintains its own clock, and doesn't need it.

/usr/src/linux/arch/i386/kernel/time.c

do_timer_interrupt()

It is accessed, around once every 11 minutes it seems, though I'm not entirely
certain under what circumstances STA_UNSYNC is set, I didn't trace it that
deeply.

In any case, /dev/rtc has many uses in a running system, even if not by the
kernel itself

> Read my howto, it is documented there, and my sources for so saying.

I only read one source.

> And some (or all) of those chips are also powered from the board 5 Vcc
> while powered up.

OK, that is interesting. Then maybe this debate is entirely pointless :)

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