I too noticed that RT linux does not compute gettimeofday correctly for
pentiums (I don't know about other processors). I tracked the problem down
to a synchronization issue between the RT clock and the Linux clock. I
fixed the problem, which requires changes to the linux kernel in
arch/i386/kernel/time.c and rtl_time.c. I don't know what to do with these
changes.
Robert Kavaler
[EMAIL PROTECTED]
Geir Sagvolden wrote:
> Hi,
>
> I've been using RT-Linux v1.1 & kernel 2.0.36 since april in a
> distributed data-logging app with great success :). However, when
> recently upgrading to 2.2.13 and v2.0, I have experienced problems in
> using timestamps for data synchronisation.
>
> My rt-module fires at the parallel port IRQ to retrieve data at a rate
> of ~1kHz. The previous version used the system call do_gettimeofday() to
> add an UTC timestamp to the sample. When upgrading, the times returned
> by the system show considerable jitter (typ. 5 milliseconds, and even
> negative time increments), while the time returned by clock_gettime is
> nicely monotonic.
>
> However, I NEED to read the absolute system time to be able to
> synchronize data retrieved by different computers in a distributed
> system. I use the xntp to lock the system time of each computer in the
> data retrieval system to about 1 sample precision, which allows
> subsequent data alignment.
>
> I have seen that there has been some discussion in the kernel lists
> about non-monotony of the system time, so this may be a problem related
> to the 2.2.X kernel and not to RTL, but any suggestions on how to get
> around this problem is appreciated.
>
> Thanks,
> Geir Sagvolden
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