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 > > > > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > -- Chris Albertson Redondo Beach, California _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
