[Xenomai-help] Huge clock drift

[Jonas Witt <jonas.witt@domain.hid>]

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