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From:	philippe <philippe DOT meynard AT vendeeconcept DOT com>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: jitter between 2 hardware interrupt
Date:	Mon, 8 Mar 2010 01:33:44 -0800 (PST)
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On Mar 6, 4:13=C2=A0pm, RayeR <gl DOT  DOT  DOT  AT centrum DOT cz> wrote:
> I suspect that this behavior have something to do with PC SMBIOS/SMI.
> This is heavily used in modern PC for power management, error
> signalling and even emulating legacy hardware.
>
> CPU can be set in real mode, protected mode and SMM (System Management
> Mode) mode.
> SMM mode is entered when SMI (System Management Interrupt) is
> triggered.
> CPU has separated SMI pin that is fed from chipset. It has higher
> priority than NMI and I think it
> cannot be disabled for safety reasons. When SMI occured CPU switch to
> SMI handler.
> This is done in real mode as well as in protected mode. Entire CPU
> context is saved.
> SMI handler determine the cause of SMI and call the matching service.
> It can take some time of course.
> Finally it restore CPU context and switch back to RM/PM. So running
> operating system cannot recognize
> this interrupt. I think this approach is also used for USB storages
> emulating real drives. SMI
> BIOS cannot be completly disabled but by disabling some legacy support
> or power management stuff
> you may save some time... If you run your program on some old 486 or
> Pentium 1 you should
> notice much less jitter caused by this.
>

it's possible to disable it ?

> Next I give you warning when using RDTSC. On mobile systems there are
> various power saving features
> like intel speedstep or EIST that cause CPU clock mudulation or
> dynamic core multiplier change which
> cause that you cannot rely on TSC that it runs on constant speed! I
> had some bad story with this when
> trying to use TSC for some short time measurement.
>

yes, but I test on 2 or 3 minutes and I have the jitter. I don't think
that CPU clock change during this testing. But for a long test, I
should be careful!


> On 4 b=C5=99e, 20:07, "Josep M." <josepma DOT  DOT  DOT  AT turomas DOT com> wrote:
>
>
>
> > I don't know why, but there are som bios task wich interrupts processor=
 and
> > I can not disable too.- Hide quoted text -
>
> - Show quoted text -

thanks for your help, I looking for disable this interrupt on the net.

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