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* [Xenomai-help] Huge clock drift
@ 2011-05-26 17:28 Jonas Witt
  2011-05-27  6:40 ` Gilles Chanteperdrix
  0 siblings, 1 reply; 19+ messages in thread
From: Jonas Witt @ 2011-05-26 17:28 UTC (permalink / raw)
  To: xenomai

Hi all,

i am having a problem concerning the clock drift under load:

# /usr/xenomai/bin/clocktest
== Tested clock: 0 (CLOCK_REALTIME)
CPU      ToD offset [us] ToD drift [us/s]      warps max delta [us]
--- -------------------- ---------------- ---------- --------------
   0          775571614.0       166776.858          0            0.0


It remains in the hundreds of MILLIseconds, changing constantly. My 
setup consists of an embedded Intel Atom board (1.6GHz Z530 processor) 
with a 2.6.32.7 kernel and Xenomai 2.5.2. Latencies under load are 
reasonable. Mean latency < 10us. Maximum latency < 40us.

Without load the ToD offset is approximately constant over time with a 
ToD drift in the range of 10 microseconds (strangely after a while this 
settles in a range of 2 microseconds). Does anyone have an idea how this 
can be caused? As a workaround I currently use rt_timer_read() in all 
relevant programs (also the non-realtime ones), since I need consistent 
timestamps between realtime and non-realtime tasks.

One other (maybe unrelated) strange behavior is occasional secondary 
mode switches when calling rt_queue_read(...).

Any help would be appreciated. Thanks in advance!

Cheers,
Jonas



^ permalink raw reply	[flat|nested] 19+ messages in thread

end of thread, other threads:[~2011-05-30 13:08 UTC | newest]

Thread overview: 19+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2011-05-26 17:28 [Xenomai-help] Huge clock drift Jonas Witt
2011-05-27  6:40 ` Gilles Chanteperdrix
2011-05-27 14:19   ` Jonas Witt
2011-05-27 14:38     ` Gilles Chanteperdrix
2011-05-27 15:05       ` Jan Kiszka
2011-05-27 16:22         ` Gilles Chanteperdrix
2011-05-27 18:29         ` Jonas Witt
2011-05-27 19:11           ` Gilles Chanteperdrix
2011-05-28 14:32             ` Jan Kiszka
2011-05-28 22:08               ` Gilles Chanteperdrix
2011-05-29 15:38                 ` Jan Kiszka
2011-05-30  7:03               ` Pavel Machek
2011-05-30  7:07                 ` Jan Kiszka
2011-05-30  7:43                   ` Jonas Witt
2011-05-30  7:57                     ` Jan Kiszka
2011-05-30 10:31                       ` Jonas Witt
2011-05-30 10:33                         ` Pavel Machek
2011-05-30 12:32                           ` Jonas Witt
2011-05-30 13:08                             ` Jan Kiszka

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