[Xenomai-help] Timer frequency

[Xenomai-help] Timer frequency

[karre]

Hi folks,

does Xenomai adjust the system timer frequency? I probably does, so how can I find out the frequency on my system?

Thanks,

Richard
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Re: [Xenomai-help] Timer frequency

[Gilles Chanteperdrix]

karre@domain.hid wrote:
 > Hi folks,
 > 
 > does Xenomai adjust the system timer frequency? I probably does, so how can I find out the frequency on my system?

See:
http://www.xenomai.org/documentation/branches/v2.3.x/html/api/group__native__timer.html#g66f026b0ac68ef3acde0e6d1bdb6baaf

In short, by default, the system timer is handled in aperiodic mode,
which means that there is no timer frequency: the system timer is
programmed at each software timer event to tick at next event. 

If you are using the stable version or previous releases, the system
timer can be set to periodic mode at compilation time or by passing
parameters to skins modules.

Xenomai trunk emulates periodic mode over aperiodic mode and allows to
set for each skin whether it will use the aperiodic timer, or an
(emulated) periodic timer.

-- 


					    Gilles Chanteperdrix.

Re: [Xenomai-help] Timer frequency

[karre]

Hi Gilles,

Thank you for your answer!

Does the Linux-Kernel need to be triggered every now and then to adjust system clock? I know that in times of DOS, the system timer had to occur every 18.3 seconds, and I have heard that Linux adjusted this for better scheduling. Do you know how often Xenomai issues a timer irq during idle phases?

Thanks in advance,

Richard
-------- Original-Nachricht --------
Datum: Fri, 20 Apr 2007 22:27:16 +0200
Von: Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>
An: karre@domain.hid
CC: xenomai@xenomai.org
Betreff: Re: [Xenomai-help] Timer frequency

> karre@domain.hid wrote:
>  > Hi folks,
>  > 
>  > does Xenomai adjust the system timer frequency? I probably does, so how
> can I find out the frequency on my system?
> 
> See:
> http://www.xenomai.org/documentation/branches/v2.3.x/html/api/group__native__timer.html#g66f026b0ac68ef3acde0e6d1bdb6baaf
> 
> In short, by default, the system timer is handled in aperiodic mode,
> which means that there is no timer frequency: the system timer is
> programmed at each software timer event to tick at next event. 
> 
> If you are using the stable version or previous releases, the system
> timer can be set to periodic mode at compilation time or by passing
> parameters to skins modules.
> 
> Xenomai trunk emulates periodic mode over aperiodic mode and allows to
> set for each skin whether it will use the aperiodic timer, or an
> (emulated) periodic timer.
> 
> -- 
> 
> 
> 					    Gilles Chanteperdrix.

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Re: [Xenomai-help] Timer frequency

[Gilles Chanteperdrix]

karre@domain.hid wrote:
 > Hi Gilles,
 > 
 > Thank you for your answer!
 > 
 > -------- Original-Nachricht --------
 > Datum: Fri, 20 Apr 2007 22:27:16 +0200
 > Von: Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>
 > An: karre@domain.hid
 > CC: xenomai@xenomai.org
 > Betreff: Re: [Xenomai-help] Timer frequency
 > 
 > > karre@domain.hid wrote:
 > >  > Hi folks,
 > >  > 
 > >  > does Xenomai adjust the system timer frequency? I probably does, so how
 > > can I find out the frequency on my system?
 > > 
 > > See:
 > > http://www.xenomai.org/documentation/branches/v2.3.x/html/api/group__native__timer.html#g66f026b0ac68ef3acde0e6d1bdb6baaf
 > > 
 > > In short, by default, the system timer is handled in aperiodic mode,
 > > which means that there is no timer frequency: the system timer is
 > > programmed at each software timer event to tick at next event. 
 >
 > Does the Linux-Kernel need to be triggered every now and then to
 > adjust system clock? I know that in times of DOS, the system timer
 > had to occur every 18.3 seconds, and I have heard that Linux adjusted
 > this for better scheduling. Do you know how often Xenomai issues a
 > timer irq during idle phases?

On most architectures, one of the tasks of Xenomai nucleus is to handle
a periodic software timer which emulates the system timer used by
Linux. The frequency of this timer is the same as the one expected by
Linux, it depends on CONFIG_HZ.

There is at least on exception to this scheme: the x86 with local
APIC. In this case, Xenomai uses the local APIC as system timer, and
Linux continues to use the PIT.

-- 


					    Gilles Chanteperdrix.