Hi,

thanks for your help: now I can compile!

May I ask you which kind of \"Real-Timeness\" can I achieve on a non-RTAI Linux System?
On the documentation I found that is possible to program loops up to 5 ms, but is that
sampling time good enaugh?

Giulio

Hello Giulio,

If you set root as owner to the plc-program it will run with SCHED_FIFO (real-time scheduling) at the priority you have configured. Set group to the same group as your own user belongs to and then also set the s-bit. If you do the same thing to $pwr_exe/rt_prio the rest of the run-time processes will run with a proper scheduling.

What scan-time is possible is really depending on the kernel you are running. We run 2.6.18 with HZ set to 1000. In the newer kernels it is possible to configure an other scheduler than the ordinary O(1)-scheduler. This scheduler is tickless (CFC-scheduler) and I think it is possible to run faster. Never tried it. In the next couple of months I will make some tests. You could also compile the kernel with HZ > 1000 to be able to run faster. Never tried this either.

5 ms is good enough for most applications. Fast positioning and hydraulic-control could need shorter scan-times. Usually we never run faster than 20 ms which is enough for almost all types of machine-control.


/ Robert