From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Rune Torgersen <runet@innovsys.com>
Cc: linuxppc-dev@ozlabs.org, linuxppc-embedded@ozlabs.org
Subject: RE: Override timer interrupt
Date: Tue, 16 Oct 2007 06:55:53 +1000 [thread overview]
Message-ID: <1192481753.11795.25.camel@pasglop> (raw)
In-Reply-To: <DCEAAC0833DD314AB0B58112AD99B93B037D4F05@ismail.innsys.innovsys.com>
On Mon, 2007-10-15 at 11:49 -0500, Rune Torgersen wrote:
>
> The main couse is that our main bus frequency cannort be divided into
> 1kHz evently by the decrementer.
> Main bus freq = 99532800 Hz.
> Decrementer then becomes 24883, which gives us 999991.9624485600nsec
> per
> jiffy.
> That is not a number easilly converted into time without drift.
>
> Changing HZ to 100 fixes it, but is for varous reasons not an option
> right now.
>
> What I did do is change the timer interrupt to be called by an
> ecxternal
> 1kHz interrupt source instead of the decrementer.
>
> The TB register is only ued for offsets from the last jiffie, not as a
> continous offset, so then it works out pretty good.
> There is a discontinuity in the sub ms resolution of the clock that I
> can live with. msec and up are dead accurate.
The date is derived from the absolute TB value though...
Ben.
next prev parent reply other threads:[~2007-10-15 20:55 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-10-12 20:43 Override timer interrupt Rune Torgersen
2007-10-12 21:30 ` Mark A. Greer
2007-10-12 21:39 ` Rune Torgersen
2007-10-12 21:55 ` Mark A. Greer
2007-10-12 22:58 ` Benjamin Herrenschmidt
2007-10-15 16:49 ` Rune Torgersen
2007-10-15 20:55 ` Benjamin Herrenschmidt [this message]
2007-10-15 21:50 ` Rune Torgersen
2007-10-15 21:58 ` Benjamin Herrenschmidt
2007-10-15 23:30 ` Paul Mackerras
-- strict thread matches above, loose matches on Subject: below --
2007-10-12 20:49 Rune Torgersen
2007-10-12 21:32 ` Mark A. Greer
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