Re: orocos core documentation

Peter Soetens wrote:
> On Wednesday 08 October 2003 00:55, you wrote:
> 
>>Peter Soetens wrote:
>>
>>>LXRT is explained on my homepage
>>>http://people.mech.kuleuven.ac.be/~psoetens/portingtolxrt.html
>>
>>Having looked at "/Introducing the Real Time Application Interface
>>(RTAI) for Linux/" paper (Mantegazza, Bianchi, Dozio), I'm a bit
>>confused with their suggestions of use with LXRT and what I interpreted
>>yours to be. Correct me if I'm wrong, but are you working on creating an
>>'end product' which will attempt to be 'hard real-time' operating in
>>'user space'?
>>The above-mentioned paper describes this as 'firm real-time', and a
>>/method/ in which to develop code...
>>
>>/"when the developer is satisfied with a task's performance within LXRT,
>>the task is simply recompiled as a module and inserted into the kernel
>>(along with the associated modules which provide RTAI's real-time
>>features) to transition _from firm to hard real-time_."/
>>
>> From this, my understanding is that during development LXRT can be used
>>to develop and debug, but ultimately the final product should be
>>compiled into a kernel module.
> 
> 
> This is only true if your application is not using _any_ userspace library, 
> not even libc ...
> 
> 
>>Has the /RTAI-wind/ made this document redundant, or is your suggested
>>use of LXRT just another approach?
> 
> 
> As you guessed, that paper is a bit outdated. The general consensus is now 
> that most realtime applications can and will run under LXRT, and never go to 
> kernel space. This is simply explained by the fact that no complex 
> application can run in the kernel because of the absence of libraries. Look 
> at what is happening with the original Linux itself : first someone writes a 
> new piece of kernel functionality (like a http server, a WLAN Access 
> Point, ....), because of the limited possibilities, the application moves to 
> userspace only leaving a small kernel module behind to communictate with the 
> hardware or serialize user requests. This is exactly what is happening with 
> RTAI on a whole. Only RT-device drivers will reside in the kernel, the 
> RT-programs will run under LXRT. It incurs some overhead, but opens losts of 
> possibilities.

We have some experience in using (NEW)LXRT
in relation with the hard real-time usage
of our general purpose multibody simulation
software MBDyn (http://www.aero.polimi.it/~mbdyn)

Peter is right; you can use his document and
Herman's general purpose tutorial on real-time
for a better view of RTAI and (NEW)LXRT.

In any case, even if the README.LXRT document
might be a bit outdated, you probably missed
README.EXTENDED_LXRT and newlxrt/README.

The new approaching development thread is
committed to a huge effort for better docs.

Pierangelo.

> 
> Peter
> 



-- 
Dr. Pierangelo Masarati               | voice: +39 02 2399 8309
mailto:[email protected]  | fax:   +39 02 2399 8334
http://www.aero.polimi.it/~masarati
Dip. Ing. Aerospaziale Politecnico di Milano,
via La Masa 34, 20156 Milano, Italy