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Date: Mon, 07 Jan 2008 10:49:11 +0100
From: Jan Kiszka <jan.kiszka@domain.hid>
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Subject: Re: [Xenomai-help] Large (negative) latency test results and fast
 PC clock
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To: vikesh rambaran <vikesh.rambaran@domain.hid>
Cc: xenomai@xenomai.org

vikesh rambaran wrote:
> ...
> How does xenomai select the timerdev and the clockdev from the following
> kernel config parameters ?
> 
> a) X86_LOCAL_APIC
> b) X86_IO_APIC
> c) X86_GOOD_APIC
> d) X86_UP_APIC
> e) M586TSC
> f) X86_TSC
> g) HPET

To answer this question (for x86-32 aka i386):

Timer = X86_LOCAL_APIC ? LAPIC : PIT
Clock = X86_TSC ? TSC : PIT-emulated TSC

X86_UP_APIC controls the availability of X86_LOCAL_APIC on UP, M586TSC
(or better) enables X86_TSC. X86_IO_APIC and X86_GOOD_APIC have no
relevance here (the latter just influence the way the APIC is accessed
on i386). HPET_TIMER has that well-known side-effect of blocking the PIT
in case there is actually HPET hardware available and used by Linux.

Jan

-- 
Siemens AG, Corporate Technology, CT SE 2
Corporate Competence Center Embedded Linux