Re: [CAD_CAM_EDM_DRO] Minimum hardware for EMC

Mark Peugeot wrote:

> >
> > No, the RT task does not swap, or wait for swaps to finish.
> >
>
> Sounds like a bad idea... maybe the RT task does not swap but I think
> your
> resolution would have to suffer to make up for the overhead.

No, you have no understanding of how the RT-Linux system works.
Swapping
is a function of Linux. The RT scheduler runs 'closer' to the hardware
than
the Linux scheduler, and has complete priority over the CPU. It doles
out
available CPU time that the RT tasks don't need for Linux to use as it
desires.
But, when the RT task needs the CPU, it GETS it!

The servo control loops, trajectory generation and motion planning are
all
real time tasks that run at different rates. They are all
non-swappable, and
could care less whether swapping, or anything else, for that matter, is
going on. In fact, Linux can crash completely, and the motion control
will
just continue doing everything that it has in its buffer, until it runs
out
of work to do. Then it will just come to a smooth stop and wait for
more
work to come in. I have had this happen when testing certain versions
of the EMC software that were not compatible with all Linux revs.

In other words, ALL time-critical tasks are totally outside the purview
of Linux, once they are started, and nothing Linux can do woll starve
them
for CPU time when they need it. They run EVERY tick of their clock,
and do their work exactly on time, every time, no matter what else is
happening on the system. The GUI may become sluggish, or even stall
in some cases, but the motion control will run at exactly the programmed

speed, no matter how slow the screen updates.

Jon