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Re: calibrating MIPS counter frequency

To: Ralf Baechle <>
Subject: Re: calibrating MIPS counter frequency
From: "Maciej W. Rozycki" <>
Date: Thu, 29 Nov 2001 16:21:46 +0100 (MET)
Cc: Jun Sun <>,
In-reply-to: <>
Organization: Technical University of Gdansk
On Fri, 30 Nov 2001, Ralf Baechle wrote:

> 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.

 On the contrary, the DECstation's undocumented I/O ASIC FCR (free running
counter) driven by the TURBOchannel bus clock is said to be much more
accurate than the DS1287 used there.  And it's David L. Mills who says so,
thus we may safely assume it's true. :-)

+  Maciej W. Rozycki, Technical University of Gdansk, Poland   +
+        e-mail:, PGP key available        +

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