Re: [Xenomai-help] parallelport module for measuring external interrupt latency

[Jan Kiszka <jan.kiszka@domain.hid>]

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Markus Franke wrote:
> Jan Kiszka wrote:
>> Even if the notification is not time-critical, you first have to get out
>> of the Xenomai context in a sane manner. rtdm_nrtsig may help if you
>> don't want to use the RT scheduler for user task wakeup.
> 
> OK. Thank you for the hint with rtdm_nrtsig_*. The kernel-module works now.
> 
> But I have still a problem when generating interrupts with a high
> frequency, let's say 100us. Then I get large latencies in the range of
> 1,5 seconds. Can you see any reason for this. An intervall of 1ms works
> without any problems and the latencies reach maybe 13us in worst case.

Unless you have a very slow hardware that already overruns at 10 KHz
(rather unlikely) or some SMI-related latencies bite you (see
TROUBLESHOOTING) - I have no clue right now. Do standard Xenomai tests
show similar abnormal latencies?

If no, you may want to try the ipipe latency tracer: enable it in the
kernel hacking section and put a xntrace_user_freeze() in your
application right after when it detected some extreme latency. See the
wiki for more details on the tracer.

Jan


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