[iPAQ] RE: iPAQ Digest, Vol 16, Issue 6

Hi Val,

>
> But I've tried with nanosleep, should be better ... but I think I can
> hardly go precisely under the 10ms precision of the OS (I
> suppose it is
> 10ms since it is so on x86 linux) ...

Yes, typically a standard Linux kernel has an imprecision in the range between 1-10ms depending on Cpu Power, HW usage, etc.
So it's hard to achieve your needed precision without a realtime extension.

>
> So I have another question : what linux/distro would you
> recommand me to
> have RT Linux (on the IPAQ of maybe on x86 for other appz) ?
>

RTAI (www.rtai.org as already suggested) is a well documented, open and supported (by third party companies) RT extension for Linux.
There're also some distro and sdk based on RTAI, look at www.denx.de & www.sysgo.de, as they support also ARM architecture.
Look at this page for a comparison between OS RTAI and propetary RTLinux (which shares the same RT approches):
http://bernia.disca.upv.es/rtportal/comparative/rtl_vs_rtai.html

And here are some benchmark showing differences between an RT enabled kernel vs. standard one:
http://www.linuxdevices.com/articles/AT6320079446.html

RTAI it's already used for motion control and robot automation, so I think it can well fit in your requirements.
Not last, an RTAI device can be controlled by high level GUI such as Matlab/Simulink or Scilab/Scicos and the RTAI kernel can be traced with LinuxTraceToolkit www.opersys.com/LTT/

Obviously there're other options, like MontaVista HardHat, LynuxWorks Bluecat, etc. but all relies on low latency patches and can't guarantee microsecond (or even sub ms) worst case.

Regards
Adamo
Received on Thu Apr 15 09:19:42 2004