[okl4-developer] Timer tick length

[Geoffrey Lee]

On Mon, Sep 24, 2007 at 11:50:51AM +0930, Peter Nguyen wrote:
> Hi,
> 
> In reference to my original question, i was referring to L4 across
> architectures.  The ia32 build uses a timer tick length of 1953 u-secs
> and i was just wondering about how this was obtained (ie. does the intel
> documentation mention this or is this determined somehow via some sort
> of equation).
> 

Hi Peter,

The tick should be chosen in such a way that balances the cost of 
processing the timer tick versus the cost of blocking other threads from
running due to a cpu-intensive thread.

The exact tick that can be used will be limited by what the hardware
can provide, in the case of ia32 (non-apic) the value is chosen 1953, which
will give approximately 2 milliseconds.

As Ben mentioned previously, the plan is to enable variable length
timers, so that a constant tick will not be needed.


> Peter

	 - gl
> 
> On Mon, 2007-09-24 at 12:00 +1000, developer-request at okl4.org wrote:
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> > Today's Topics:
> > 
> >    1. Does OKL4 for pxa270 change any clock/frequency	setting?
> >       (kashin Lin)
> >    2. Re: Does OKL4 for pxa270 change any	clock/frequency setting?
> >       (Ben Leslie)
> >    3. Timer tick length (Peter Nguyen)
> >    4. Re: Timer tick length (Ben Leslie)
> > 
> > 
> > ----------------------------------------------------------------------
> > 
> > Message: 1
> > Date: Sun, 23 Sep 2007 17:15:45 +0800
> > From: "kashin Lin" <kashin08 at gmail.com>
> > Subject: [okl4-developer] Does OKL4 for pxa270 change any
> > 	clock/frequency	setting?
> > To: developer at okl4.org
> > Message-ID:
> > 	<6bd1be890709230215m3fc928p820d6cd3c7a4ed98 at mail.gmail.com>
> > Content-Type: text/plain; charset="iso-8859-1"
> > 
> > Hi,
> > 
> > i wonder whether OKL4( include l4[pistachio] & l4linux[WOMBAT]) modify the
> > value
> > in CCCR & CLKCFG? or just use default value in those registers?
> > 
> > my develop board have some bugs when using the wrong clock/frequency setting
> > ,
> > so i must check it.
> > 
> > thanks for your answering.
> > -------------- next part --------------
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> > ------------------------------
> > 
> > Message: 2
> > Date: Mon, 24 Sep 2007 10:03:47 +1000
> > From: Ben Leslie <benno at ok-labs.com>
> > Subject: Re: [okl4-developer] Does OKL4 for pxa270 change any
> > 	clock/frequency setting?
> > To: kashin Lin <kashin08 at gmail.com>
> > Cc: developer at okl4.org
> > Message-ID: <20070924000347.GD1203 at cse.unsw.edu.au>
> > Content-Type: text/plain; charset=us-ascii
> > 
> > On Sun Sep 23, 2007 at 17:15:45 +0800, kashin Lin wrote:
> > >Hi,
> > >
> > >i wonder whether OKL4( include l4[pistachio] & l4linux[WOMBAT]) modify the
> > >value
> > >in CCCR & CLKCFG? or just use default value in those registers?
> > >
> > >my develop board have some bugs when using the wrong clock/frequency setting
> > >,
> > >so i must check it.
> > >
> > >thanks for your answering.
> > 
> > 
> > Hi Kashin,
> > 
> > We generally just leave this alone and print out what is configured by
> > the bootloader.  The relevant code to look at is
> > /pistachio/platform/pxa/src/timer.cc
> > 
> > Cheers,
> > 
> > Ben
> > 
> > 
> > 
> > ------------------------------
> > 
> > Message: 3
> > Date: Mon, 24 Sep 2007 10:08:25 +0930
> > From: Peter Nguyen <peter.nguyen at adelaide.edu.au>
> > Subject: [okl4-developer] Timer tick length
> > To: developer at okl4.org
> > Message-ID: <1190594305.30470.0.camel at localhost>
> > Content-Type: text/plain
> > 
> > Hi,
> > 
> > Is the timer tick length used fixed across all implementations?
> > 
> > Peter
> > 
> > 
> > 
> > ------------------------------
> > 
> > Message: 4
> > Date: Mon, 24 Sep 2007 11:15:18 +1000
> > From: Ben Leslie <benno at ok-labs.com>
> > Subject: Re: [okl4-developer] Timer tick length
> > To: Peter Nguyen <peter.nguyen at adelaide.edu.au>
> > Cc: developer at okl4.org
> > Message-ID: <20070924011518.GC2063 at cse.unsw.edu.au>
> > Content-Type: text/plain; charset=us-ascii
> > 
> > On Mon Sep 24, 2007 at 10:08:25 +0930, Peter Nguyen wrote:
> > >Hi,
> > >
> > >Is the timer tick length used fixed across all implementations?
> > >
> > 
> > Hi Peter,
> > 
> > Do you mean across different L4 implementations or different
> > architectures in OKL4. In both cases the timer tick length ends
> > up being implementation specific. 
> > 
> > Part of our anticipated development is to enable variable length
> > timers, so that rather than a constant tick, timer interrupts
> > are only received at the end of the current thread's timeslice.
> > 
> > Cheers,
> > 
> > Ben
> > 
> > 
> > 
> > ------------------------------
> > 
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> > 
> > End of Developer Digest, Vol 6, Issue 19
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