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Re: calibrating MIPS counter frequency

To: Jun Sun <jsun@mvista.com>
Subject: Re: calibrating MIPS counter frequency
From: Ralf Baechle <ralf@oss.sgi.com>
Date: Fri, 30 Nov 2001 02:02:40 +1100
Cc: linux-mips@oss.sgi.com
In-reply-to: <3C05646B.51BF79FB@mvista.com>; from jsun@mvista.com on Wed, Nov 28, 2001 at 02:25:47PM -0800
References: <3C05646B.51BF79FB@mvista.com>
Sender: owner-linux-mips@oss.sgi.com
User-agent: Mutt/1.2.5i
On Wed, Nov 28, 2001 at 02:25:47PM -0800, Jun Sun wrote:

> In the future, I think mips counter frequency really should go to mips_cpu
> structure.  If we always know the counter frequency, either by board setup
> routine or runtime calibration, we can get rid of the gettimeoffset
> calibration routines.

Better stick with the calibration procedure.  The crystal oscilators used
in most computer systems don't provide the high accuracy of frequency
that is required to keep the clock accurately over long time.  An RTC
chip which you'd probably use as reference clock is better at that so
should be used as the ultimate reference time in the kernel.

  Ralf

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