Isn't true that when the scheduler is in periodic mode, the timer is not
reprogrammed, but yet jitter of around 15 us can still be observed under
some circumstances. Why is this?
Victor Iannello
Synchrony Inc.
----- Original Message -----
From: <[EMAIL PROTECTED]>
To: "Norm Dresner" <[EMAIL PROTECTED]>
Cc: <[EMAIL PROTECTED]>; "rtlinux mailing list" <[EMAIL PROTECTED]>
Sent: Tuesday, December 12, 2000 10:47 PM
Subject: Re: [rtl] Interrupt Jitter
> On Tue, Dec 12, 2000 at 07:29:23PM -0500, Norm Dresner wrote:
> > Can you be more specific about the source of the jitter on the
motherboard?
>
> Our measurements show it to be the ISA interface and the use of the 8253/4
> timer on the other side of the interface. There is a simple experiment
that
> we should include in the RTL distribution that does
>
>
> read cycle timer
> read 8253 register
> read cycle timer
> compute difference
>
> The computed difference was up to 15 microseconds or so when I last did
the
> experiment on a fast x86.
> Our Elan420 boards do much much better.
>
> >
> > Norman Dresner
> > Fellow Systems Engineer
> > Radar Systems Engineering Department
> > Electronic Systems and Sensors Segment
> > Northrop Grumman Corporation
> > MS 520
> > Box 746
> > Baltimore MD 21203
> >
> > Voice: (410) 993 - 2096 Mornings; all-day voice-mail
> > (410) 969 - 8068 Afternoons with answering machine
> > FAX: (410) 993 - 8084 On-site
> > (410) 969 - 8068 Afternoons; call first to arrange
> > E-Mail:Mornings: [EMAIL PROTECTED]
> > Afternoons: [EMAIL PROTECTED]
> >
> >
> > At 03:58 PM 12/12/00 -0700, [EMAIL PROTECTED] wrote:
> > >It's the motherboard design, not the chip. We get amazing performance
> > >on some more integrated chips.
> > >
> > >On Tue, Dec 12, 2000 at 03:39:12PM -0500, [EMAIL PROTECTED]
wrote:
> > >>
> > >> I've heard from many of you that x86 architecture is fundamentally
limited
> > >> to no better than a worst case interrupt latency of ~20us. Victor
even
> > >> alludes to this in his RTLinux White Paper. Does anyone know of a
source I
> > >> can reference that spells this out in detail with an explanation?
> > >>
> > >> -Chuck
> > >>
> > >> -- [rtl] ---
> > >> To unsubscribe:
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> > >> ---
> > >> For more information on Real-Time Linux see:
> > >> http://www.rtlinux.org/rtlinux/
> > >
> > >--
> > >---------------------------------------------------------
> > >Victor Yodaiken
> > >Finite State Machine Labs: The RTLinux Company.
> > > www.fsmlabs.com www.rtlinux.com
> > >
> > >-- [rtl] ---
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> > >---
> > >For more information on Real-Time Linux see:
> > >http://www.rtlinux.org/rtlinux/
> > >
> > >
>
> --
> ---------------------------------------------------------
> Victor Yodaiken
> Finite State Machine Labs: The RTLinux Company.
> www.fsmlabs.com www.rtlinux.com
>
> -- [rtl] ---
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