Re: Pure Linux instead of RTAI

Hi Patrycjusz,

On Friday 25 November 2005 15:22, Patrycjusz Szczepaniak wrote:
[...]
>
> It turned out that I do not have to use RTAI for my application to work. I
> changed a systemclock frequency (values of a HZ and a CLOCKS_PER_SEC
> variables located in a /usr/src/linux-2.4.25/include/asm-i386/param.h file)
> and recompiled a kernel. The old value equal 100 was changed to 1000.

Not bad, we used the 2.6 kernel (ran also at 1000Hz) to control a Kuka 160 
using comedilib and got it also running at comparable rate. Lateron, we 
recompiled for LXRT, for reasons given below.

>
> It solved my problems. It seems that scheduler switched processes too
> rarely that is why they were not executed in time. Now my regulators are
> being executed every 2000us +-2us.
>
> I executed my application with the highest priority during a high system
> load (I was compiling a kernel) and it still worked just fine.
>
> Is there any sense in using RTAI if Linux works?

It depends on how expensive your robot+tools are :-) At some moment, you
may miss a deadline at a bad time (for example, close to an obstacle) and 
crash into something. With a real-time operating system, this will not happen 
at all. Now, the numbers you give are quite impossible, since even typical 
hardware induced jitter is about 30us, thus an order larger than your 2us.
That said, if you ever plan selling that computer, you'll have no problem to 
find a buyer ;-)

Which Orocos version are you using ?

Peter