On 2/19/26 12:59, Bari wrote:
On 2/18/26 2:25 PM, Bertho Stultiens wrote:
On 2/18/26 8:01 PM, Bari wrote:
Since RTAI has reached the end of its life the way forward might be
Xenomai 4 https://evlproject.org/overview/
How many users might find this useful?
The few that require systems with lower latency than preempt_rt can
provide. There are a few of us.
And there are tricks to make preempt-rt better. I've invented a third
IRQ thread back when I was trying to use an RPI3b to drive my lathe. I
still use that for the much faster rpi4b. Actually real simply done. I
defined a new. slower because humane hands aren't that fast, 200 hz
thread and moved all my hand inputs to it, like the encoder dials that
effectively replace the cranks that left with the removal of the factory
apron. I replaced the apron by tapping for 8 1/4" bolts into the front
face of the carriage and replaced the apron gearbox with a panel of
1/2" 7076 ALU . With a central window for the slider the X motor lives
in, equpt with a belt tightening adjuster. And a push switch (used to
trigger the motion per click adjustment in hal) and 100 PPR $22 encoders
that Jameco.com had for a long time. They are fed into the axis decoders
in a 7i90HD and wired up in .hal as replacements for the cranks that
used to be. All that stuff runs at a lower priority that the 1kilohertz
main loop. There is no fast loop, the 1khz is the fastest. And it
still can be moved faster than I can twist a dial. Dead smooth, no
clicks from data starvation like the rpi3b did originally. And it all
runs on 21 watts when the lathe power is off.
I've considered replacing those hungry wintel computers, 350 watt
burning off lease Dell's on the other 3 machines, but that kilowatt I'd
save at a cost of around $350 per machine for the whole conversion would
shift that 350 watts per machine, to the pair of electric heaters that
heat my well insulated garage, 6" walls full of cocoon and a foot of it
on the ceiling. So the net power saving would be zip. But except for
that consideration I now wish I had used something like a bananapi-m5 to
do all my now wintel powered machines.
That pi is the most stable thing running medium powered machines out
there. Back when it had a ups, (its battery died a year ago, the
replacement UPS I bought uses more power heating the battery than the pi
uses) uptimes could be years. 4 3d printers are also using pi clones &
my backup server is one of the bananapi-m5's. So yes, I would be
interested in an evl/Xenomai version for ARM64's. If I don't miss roll
call first.
Is there a pressing reason or major advantage to use Xenomai instead
of using the non-kernel module approach with stock RT-PREEMPT kernels?
I tried it once, a decade ago when I had a stack of atoms running
things, made 5 or so attempts but it wouldn't build on the atoms then. I
don't recall why now.
I don't think many have been using (older) Xenomai. There are things
referring to it in the LCNC build and source code, but I have a
feeling some bitrot may have happened. Or are there people being busy
keeping LCNC on Xenomai up-to-date?
I think that most were just using RTAI since it has been working for
decades with little effort using a low cost LPT card and BOB. If
Xenomai had been easily available, then it would of had a following as
well.
it will be lots of work and we aren't sure yet how to support Mesa
cards with it yet.
At least some Mesa cards, all Ethernet cards and currently anything
used on ARM, is userspace only. They can't be built as a kernel
module. I'm not sure it would be worth the effort trying because it
requires a *lot* of work and may be impossible for some without a
rewrite. There is a port of Xenomai to ARM, but I'm still not sure
whether it is worth the effort.
Keeping two RT systems alive in the LCNC source also requires much
better CI because we can't currently test anything kernel based. So
breakage will probably be more rule than exception.
Faster systems might require RDMA to keep up. But these are edge cases
and not hobbyist projects.
You are ignoring the speed of the pi when its running the interface on
rpspi interface. 42 megabit writes, 25 megabit reads in 32 bit packets
to/from a 7i90HD and a triplet of 7i42TA;s for 72 i/o lines. I'm doing a
lot on that lathe but have only used about half of those 72 lines for
the lathe.
Xenomai already works with EtherCat.
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Cheers, Gene Heskett, CET.
--
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soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author, 1940)
If we desire respect for the law, we must first make the law respectable.
- Louis D. Brandeis
Don't poison our oceans, interdict drugs at the src.
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