exactly....
That is what is called inter process communication (IPC) in the
computing world. There are all kinds of systems to deal with that in
large scale supercompters. individual compute nodes have a means to
communicate with other compute nodes
In this case it would mean, "hey axis Y I am axis X and and I am at
this position blabla, what position are you at?" That is not science
fiction, it
has been around for a long while and exists and works very well.
Ron
On 1/24/20 9:27 PM, Alan Condit wrote:
Chris,
If I send 10000 steps to a smart X-axis controller, how does it stay in sync
with a smart
y-axis controller without someone controlling the synchronization between the
two?
Alan
From: Chris Albertson <albertson.ch...@gmail.com>
Subject: Re: [Emc-users] Real-time OS for machine controllers
Date: January 24, 2020 at 9:48:27 AM PST
To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net>
If you can tolerate latency, then your "hub" does not need what we call
"hard" real-time capability. It only needs to keep up with the average
workload, averaged over whatever latency you can tolerate. Video streaming
works this way. They can't reliably send video and the 60 Hz frame rate
so they buffer a few seconds of video on your phone and the real-time
viewer lives on the phone not the server.
g-code could be the same way. The penalty is that when you press the "go"
button the milling machine would take a few seconds the start working while
the data buffers into the low-level motor controllers. Today a
step/direction controller has no memory so it must be fed steps in real
time. But if it has a 10,000 step memory you could just transfer blocks
ever half second and the controller would work down the queue. "Steps"
are the wrong kind of data for this but "states" are what is used.
You are correct in that some real-time ability is needed at every level.
But we could design things so the requirements are VEY loose at the highest
level for 0.5-second latencies being acceptable. One you need only that,
then even an iPhone is a good enough platform.
On Thu, Jan 23, 2020 at 11:32 AM Peter C. Wallace <p...@mesanet.com> wrote:
On Thu, 23 Jan 2020, Chris Albertson wrote:
Date: Thu, 23 Jan 2020 10:17:44 -0800
From: Chris Albertson <albertson.ch...@gmail.com>
Reply-To: "Enhanced Machine Controller (EMC)"
<emc-users@lists.sourceforge.net>
To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net
Subject: Re: [Emc-users] Real-time OS for machine controllers
The trouble with the Mesa FPGA design is that it depends on a computer
with
good real-time performance. It can generate steps but I don't thing you
can run a position or velocity PID control loop on the FPGA.
LinuxCNCs design paradigm requires realtime, this is a design decision
that is
supported by our Hostmot2 real time firmware. We have other firmware that
implements motion in the FPGA but this is not suited to LinuxCNCs model.
You might argue that its an old fashioned model but many high performance
CNC
systems and Robotics controllers use LinuxCNCs model of a capable real
time host
(real OS with file I/O loadable modules, unlimited memory, massive
floating
point performance etc etc) Some of these use Linux and others use real
time
windows varients often with Ethercat Peripherals. This makes for a
powerful
extensible realtime toolkit (like LinuxCNCs HAL) and complex realtime
responsive coordinated motion. Basically for this type of system you still
need a very capable real time controller hub even if the motor controllers
implement torque, velocity, or position loops
Peter Wallace
Mesa Electronics
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Chris Albertson
Redondo Beach, California
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