AW: RTAI calibration question
kbischop at vertexant.de
Fri Jan 20 16:01:04 CET 2006
> There has been an answer already. I would like to add a few suggestions:
> - use of calibrate is Ok but my favourite way is the use of
> "showroom/v3.x/kerne/calibration" where you can play inreractively with
> all the calibrations;
> - for the in kernel latency get a feeling of the differences that exist
> between using lxrt or ksched;
> - check differences between having a Linux load or not.
> That said you'll see that there is no unique figure. For example you
> have a machine that is almost double the speed of mine, show a better
> ISA bus access but your latencies are almost doubled. Is it a
These high latencies bother me most. The machine is a VMEbus system with a
Gefanuc VMIVME 7807 VME single board computer. It has a Pentium M with 1,8
Ghz and a Intel 6300ESB chipset.
The system is running Debian 3.1. I can boot this machine with two different
The first installation consists of a 2.4.32 kernel, patched with a legacy
RTHAL, and RTAI3.0r5. The second installation uses a 2.4.32 kernel, patched
with the proper IPIPE patch, and RTAI-3.3-test4.
The RTHAL/RTAI3.0r5 gives me the following result when I run calibrate:
LATENCY_8254 3610 (ksched)
Results from calibrate with IPIPE/RTAI3.3-test4:
SETUP_TIME_8254 1859 (same value as RTAI 3.0r5)
LATENCY_8254 7183 (ksched, nearly doubled with RTAI3.3-test4)
I don´t really understand that, it´s the same hardware, same linuxsystem.
Can you give any advice, why the latency is so bad under RTAI3.3-test4 ?
> Generally speaking for those that are not taking extreme timings, say
> less that 10/20 KHz I suggest using a calibrations value that give a
> negative average, thus anticipating sheduling time a bit so that to use
> the beasy wait scheduler featur to be as sharp as possible on the
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