Re: [Xenomai-help] sem_wait increments fault counter

[Philippe Gerum <rpm@xenomai.org>]

On Tue, 2009-05-05 at 15:44 +0200, roderik.wildenburg@domain.hid
wrote:
> Dear Gurus,
> 
> every time I call sem_wait a fault counter is incremented (TRAP 0).
> sem_wait itself does not return an error :
> 
> uc101 # cat /proc/xenomai/faults
> TRAP         CPU0
>   0:            1    (Data or instruction access)
>   1:            0    (Alignment)
>   2:            0    (Altivec unavailable)
>   3:            0    (Program check exception)
>   4:            0    (Machine check exception)
>   5:            0    (Unknown)
>   6:            0    (Instruction breakpoint)
>   7:            0    (Run mode exception)
>   8:            0    (Single-step exception)
>   9:            0    (Non-recoverable exception)
>  10:            0    (Software emulation)
>  11:            0    (Debug)
>  12:            0    (SPE)
>  13:            0    (Altivec assist)
> 
> what could be the reason for this? Is this serious?

Not necessarily on ppc. Under certain circumstances, a minor fault such
as a TLB miss may happen. Usually, 85xx is more prone to this than 6xx
though, but this does not normally affect latencies.

> I have to add that sem_wait is called form a Linux-Prozess (linked with
> xenomai libraries, but no xenomai thread is created) when this happens.
> 

Only exceptions caught on behalf of the primary domain are reported
by /proc/xenomai/faults, so somehow, this must be a real-time thread
triggering this.

> System: PPC Linux 2.4.25; Xenomai 2.3.5 
> 
> Thank you for your help
> Roderik
> 
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-- 
Philippe.