Hello,
Am 31.10.2011 12:15, schrieb Donggu Kang:
Hello,
Sorry, I didn't attache system information.
Processor : Core2 Duo L7400 1.5Ghz
Task Cycle: 1ms
Real-Time : Xenomai 2.5.6, iadeos-ipipe-2.6.37-x86-2.9-02
Linux : Debian squeeze , kernel-2.6.37.6
Etherlab : 1.5-stable
looks good, which driver do you use?
e100, 8139too, generic?
I think your latency should be about 7us.
Do you check SMI?
I did use Beckhoff I/O Module EL2088 with EK1100 Ethercat coupler.
In my xenomai reat-time task, I only turned output ON and OFF at every cycle.
And I measured a period of the output signal of I/O module using 1Ghz
Oscilloscope.
I also read CPU TSC value.
I know the period value have lots of factors, task execution time,
network latency,
ESC response time, and so on.
Xenomai guys said "when a real-time task runs in primary mode, it can
not be interrupted by
any Linux interrupt. However, a real-time task using linux services
(such as linux network services), it will switch to secondary mode, and
a linux irq will be able to interrupt it. "
Yes this is correct.
EtherLab master is working as kernel module, isn't it?.
So I think if xenomai gays says correct, when real time task call the
etherlab api, the mode is changed to secondary mode,
and hardware irq could be able to interrupt it.
No, that is not possible. Let me explain.
The etherlab master is a kernel module but for the realtime task it is
only a summary of functional code. In realtime the etherlab master does
not use kernel infrastructure. So your task will run only in primary mode.
But if you use the generic driver you use kernel infrastructure, so your
task will switch in secondary mode.
Using the native driver e100, 8139too,... will run in primary mode.
Best regards
Andreas
For more reduced latency, how can I do?
Best regards
Donggu
2011/10/24 Andreas Stewering-Bone<a...@igh-essen.com>:
Hello,
first, the use of etherlab should not touch your system latency,
Which processor do you use?
How do you measure the latency? RTAI-Testsuite?
What are your etherlab task cyclic time?
What execution time does your software have?
On older system with high hd load you can switch of dma.
Best regards
Andreas
Am 21.10.2011 06:48, schrieb Donggu Kang:
Hi,
I'm newbe in ethercat and real-time world.
I installed etherlab master(1.5-stable) with xenomai environment on my
linux box.
And I tried to latency test of real-time task with etherlab master API.
I also did it without a ehterlab master API.
A stress is "while true;do ls -lR /> /tmp/list; done& > /dev/null"
shell script;
It's called repeatedly by bash shell script and making hard disk load.
When I use etherlab API, the latest latency of cyclic task is above a
500us.
But when I don't use etherlab API, latency is about "70us".
According test result, etherlab API or EtherCAT-capable network device
is interrupted by hard disk access on my system.
I think hard disk access is making a huge latency.
And other devices also also become a source of latency on my system.
If anyone has any advice could you please leave your comment?
Best regards.
Donggu Kang.
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andreas.stewering-b...@igh-essen.com
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Ingenieurgemeinschaft IgH
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Mit freundlichem Gruß
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--
------------------------------------------------------------------------
Dipl.-Ing.(FH) Andreas Stewering-Bone
andreas.stewering-b...@igh-essen.com
Tel.: +49 201 / 36014-15
Ingenieurgemeinschaft IgH
Gesellschaft für Ingenieurleistungen mbH
Heinz-Bäcker-Str. 34
D-45356 Essen
Amtsgericht Essen HRB 11500
USt-Id.-Nr.: DE 174 626 722
Geschäftsführung:
- Dr.-Ing. S. Rotthäuser,
- Dr.-Ing. T. Finke,
- Dr.-Ing. W. Hagemeister
Tel.: +49 201 / 360-14-0
http://www.igh-essen.com
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