Re: [Xenomai-help] RTCAN and tsc

[Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>]

roland Tollenaar wrote:
> Hi
> 
> I need to be educated a bit here if you don;t mind.
> 
> arming up...
> RTT|  00:00:01  (periodic user-mode task, 1000 us period, priority 99)
> RTH|-----lat min|-----lat avg|-----lat max|-overrun|----lat best|---lat worst
> RTD|      29.333|      29.333|      31.847|       0|      29.333|      31.847
> RTD|      29.333|      29.333|      35.199|       0|      29.333|      35.199
> RTD|      29.333|      29.333|      33.523|       0|      29.333|      35.199
> RTD|      29.333|      29.333|      32.685|       0|      29.333|      35.199
> RTD|      29.333|      29.333|      34.361|       0|      29.333|      35.199
> RTD|      29.333|      29.333|      33.523|       0|      29.333|      35.199
> RTD|      29.333|      29.333|      33.523|       0|      29.333|      35.199
> RTD|      29.333|      29.333|      34.361|       0|      29.333|      35.199
> RTD|      29.333|      29.333|      32.685|       0|      29.333|      35.199
> RTD|      29.333|      29.333|      34.361|       0|      29.333|      35.199
> RTD|      29.333|      31.847|     201.142|       0|      29.333|     201.142
> RTD|      29.333|      59.504|     205.333|       0|      29.333|     205.333
> RTD|      29.333|      65.371|     201.142|       0|      29.333|     205.333
> RTD|      29.333|      68.723|     201.980|       0|      29.333|     205.333
> RTD|      29.333|      64.533|     201.142|       0|      29.333|     205.333
> RTD|      29.333|      65.371|     204.495|       0|      29.333|     205.333
> RTD|      29.333|      52.799|     201.142|       0|      29.333|     205.333
> RTD|      29.333|      65.371|     204.495|       0|      29.333|     205.333
> RTD|      29.333|      35.199|     201.142|       0|      29.333|     205.333
> RTD|      29.333|      29.333|      34.361|       0|      29.333|     205.333
> RTD|      29.333|      29.333|      33.523|       0|      29.333|     205.333
> ---|------------|------------|------------|--------|-------------------------
> 
> 
> What you see above (up to where max latecy jumps to 200) is the
> behavior while my application is running but the node (rotary encoder)
> is not moving so not sending any position signals. The moment I start
> turning the encoder shaft the jump takes place.
> 
> What does output of latency mean? Is the above result simply stating
> that I have a crappy hardware structure and will never be able to
> achieve better latency or does it tell me there is something wrong
> with my application?

Enable the I-pipe tracer, recompile your kernel, set
/proc/ipipe/trace/back_trace_points to a larger value, and run latency
with the -f flag. Show us the contents of /proc/ipipe/trace/frozen, and
we may be able to give you an answer.

For more details on the I-pipe tracer, see:
http://www.xenomai.org/index.php/I-pipe:Tracer

-- 
                                                 Gilles Chanteperdrix