Hello Thomas,
This is a known problem. If you want more information about it take a
look at this posting I did a while ago:
http://www.rtlinux.org/mailing_list/rtl.w5archive/0008/msg00239.html
One can't use use do_gettimeoday from real-time kernel modules because
it uses normal Linux locks to ensure exclusive access to xtime_lock.
Changing the Linux locks to real-time locks fixes the problem. This is
done in the LTT patch for RTAI and works great. It provides accurate
timing and enables hard-real-time tasks to access do_gettimeofday without
problems.
Cheers,
Karim
Thomas Folkers wrote:
>
> Victor,
> How come I can't get the time of day from the kernel? If I use
> do_gettimeofday(), eventually the system will hang. It may not happen
> right away, but it will hang. I'm trying to time external events and
> record the exact time an interrupt comes in and the only way to compare
> that time to other events and to other systems is to have the exact
> system time. The clock_gettime() routine returns something close to
> the real system clock time, but then proceeds to gain time at the rate of
> 35,000 nsecs/sec. That's probably due to a miss calibration in the cpu HZ
> value. I have looked over the rtl_time.c file and can see where you 'sync'
> the CLOCK_REALTIME to the results of a do_gettimeofday() call, but then
> there doesn't seem to be any other 'tweeks' to the time to keep it in
> sync. So, while the clock_gettime() produces a nice monotonic clock, it
> bear little resemblance to actual time.
> So, how do I get the time of day from the kernel?
>
> Thanks for you help,
> Tom
>
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>
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