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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