Re: [Xenomai-help] Question about getting system time

[Jan Kiszka <jan.kiszka@domain.hid>]

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[please avoid top posting]

Josh Karch wrote:
> Jan,  
> 
> If no ntp server updates are made to the Linux clock,  we have noticed over a week's period a drift of ten or so seconds difference between the Linux clock and the Xenomai get time function and often have to reboot our machine to resynchronize the Xenomai and Linux clocks back to less than a couple seconds difference.  I was wondering if you might explain why that might happen?

I assume you are talking about an x86 platform: Normally, Linux should
run on the TSC clocksource, just like Xenomai does. To ensure that the
hardware isn't broken, Linux continuously performs runtime checks. The
preemption by Xenomai tasks my fool this check an make Linux switch to a
different clocksource. Now you have unsynchronized sources that usually
drift.

I haven't tried this with Xenomai yet but I could imagine it works just
like it does in virtual machines: Pass tsc=reliable on the kernel
command line. This disables the runtime checks, thus should take away
any reason Linux may want to switch to anything else than TSC.

Jan


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