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From: "Matthias Urlichs" <smurf@smurf.noris.de>
Date: Mon, 28 Jun 2004 03:24:07 +0200
To: Chris Wedgwood <cw@f00f.org>
Cc: linux-kernel@vger.kernel.org
Subject: Re: [parisc-linux] Re: [PATCH] Fix the cpumask rewrite
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	Content preview:  Hi, Chris Wedgwood: > On Sun, Jun 27, 2004 at
	02:00:03PM +0200, Matthias Urlichs wrote: > > > <heretic> > > #define
	jiffies __get_jiffies() > > </heretic> > > Well, I have that but it's
	only part of the story. > True. [...] 
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Hi,

Chris Wedgwood:
> On Sun, Jun 27, 2004 at 02:00:03PM +0200, Matthias Urlichs wrote:
> 
> > <heretic>
> > #define jiffies __get_jiffies()
> > </heretic>
> 
> Well, I have that but it's only part of the story.
> 
True.

> As Alan pointed out a suitable API could also make it easier to work
> towards a clock-less system for embedded targets.
> 
Well, drivers do need some way of timing things, else they wouldn't read
jiffies in the first place. So, at minimum, an embedded system would
need a way to trigger a timeout at some specified time in the future.

A simple __get_jiffies() implementation could just set up a 1/HZ-second
timer (and busy-wait for it, and increase its internal jiffies counter)
every tenth call or so. That would probably slow down the whole system
somewhat, but I'd assume it'd mostly work.

-- 
Matthias Urlichs