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From: Mark Salisbury <mbs@mc.com>
To: David Schleef <ds@schleef.org>, David Schleef <ds@schleef.org>,
        Alan Cox <alan@lxorguk.ukuu.org.uk>
Subject: Re: No 100 HZ timer !
Date: Tue, 10 Apr 2001 08:19:59 -0400
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Cc: Mikulas Patocka <mikulas@artax.karlin.mff.cuni.cz>,
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On Tue, 10 Apr 2001, David Schleef wrote:
> i.e., the TSC, you have to use 8254 timer 0 as both the timebase
> and the interval counter -- you end up slowly losing time because
> of the race condition between reading the timer and writing a
> new interval.  

actually, I have an algorithm to fix that.  (had to implement this on a system
with a single 32 bit decrementer (an ADI21060 SHARC, YUK!))  the algorithm
simulates a free spinning 64 bit incrementer given  a 32 bit interrupting
decrementer under exclusive control of the timekeeping code.  it also takes
into account the read/calculate/write interval.


  
> It would be nice to see any redesign in this area make it more
> modular.  I have hardware that would make it possible to slave
> the Linux system clock directly off a high-accuracy timebase,
> which would be super-useful for some applications.  I've been
> doing some of this already, both as a kernel patch and as part
> of RTAI; search for 'timekeeper' in the LKML archives if interested.
> 
> 
> 
> 
> dave...
-- 
/*------------------------------------------------**
**   Mark Salisbury | Mercury Computer Systems    **
**   mbs@mc.com     | System OS - Kernel Team     **
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