Re: [ECOS] Maximum RTC Tick Rate

["Fred Woolsey" <fwsbcon at fwsbcon dot com>]

A deferred PS:

BTW- I made sure to bump the ticks/timeslice to 50, or 5 ms per scheduler
slice.

FCW

----- Original Message -----
From: "Fred Woolsey" <fwsbcon@fwsbcon.com>
To: "eCos Discussion" <ecos-discuss@sources.redhat.com>
Sent: Wednesday, February 12, 2003 7:45 PM
Subject: Re: [ECOS] Maximum RTC Tick Rate


> At the moment, I'm running on a test platform- a 450 MHz Pentium II Compaq
> Deskpro- probably a bit more powerful than the average embedded CPU.  The
> reason for the high clock rate is (probably) twofold- the need to
implement
> sub-ms timeouts in my app, and a lack of experience with eCos.  Currently,
I
> use the RTC to drive all the timers in my app, using
> cyg_clock_to_counter( ), with an associated alarm and a flag for signaling
> timer expiration.  If anyone has any pointers regarding a more efficient
way
> to do timing, I'm all ears!!!
>
> Cheers,
> Fred Woolsey
>
> ----- Original Message -----
> From: "Jonathan Larmour" <jifl@eCosCentric.com>
> To: "Fred Woolsey" <fwsbcon@fwsbcon.com>
> Cc: "Gary D. Thomas" <gary.thomas@mind.be>; "eCos Discussion"
> <ecos-discuss@sources.redhat.com>
> Sent: Wednesday, February 12, 2003 7:08 PM
> Subject: Re: [ECOS] Maximum RTC Tick Rate
>
>
> > Gary D. Thomas wrote:
> > > On Wed, 2003-02-12 at 16:55, Fred Woolsey wrote:
> > >
> > >>Does anyone have info on the maximum real-time clock tick frequency
that
> > >>eCos can handle on an i386 platform?  I've built a test app with a
tick
> > >>interval of 100 us, which appears to work OK.
> > >
> > >
> > > One way to determine this would be to run the standard
> > > test 'tm_basic' with CLOCK_LATENCY turned on.  This will
> > > tell you not only the time to service the clock interrupt,
> > > but also the DSR and ISR latencies associated with it.
> > >
> > > My guess is (depending on your actual hardware) that at
> > > a clock rate of 100us/tick, you're probably spending a
> > > fairly considerable percentage of time just processing
> > > those interrupts (e.g. if the "round trip" time for the
> > > clock tick as measured by 'tm_basic' is 10us, then you
> > > would be using 10% of the CPU just to handle the clock
> > > at that rate).
> > >
> > > The maximum clock rate would thus be related to how fast
> > > your hardware is and how much of the CPU you are willing
> > > to give up just to process the clock.
> >
> > Not just that. It's possible that too fast and something somewhere just
> > "doesn't work". e.g. the timer just can't be driven that fast, e.g.
> > <http://sources.redhat.com/ml/ecos-discuss/2003-01/msg00300.html>
> >
> > Jifl
> > --
> > eCosCentric    http://www.eCosCentric.com/    The eCos and RedBoot
experts
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