On Sunday 24 June 2018 15:34:19 Chris Albertson wrote: > Your buffer reading example is, I think a better example of soft real > time. Typically the way this is done is not to trigger on "buffer > full" but use a 70% threshold. My definition of "soft" means that it > must be fast enough to get the work done but there is some room for > when each part of the job needs to get done > > "Hard" usesusaly has a numeric duration or rate requirement with a > "small" tolerance. "Small is kind of imprecise and could be anything > from milliseconds to nanoseconds. > > A good example of a hard real time requirement is closer to what we > do here -- motion control. But also run a PID loop at 100 Hz or maybe > to output analog signal at 48,000 samples per second to synthesize > some waveform you need. > > What we have is the result of historic accident. EMC and machine > control in general got its start when computers where EXPENSIVE. You > design differently when you parts for five digit price tags than when > you parts are nearly free. If computers cost $2 and two of them could > fit on your thumbnail then you might just be inclined to use more of > them. > > Off topic for a minute... (put I come back) > > A guy in Australia just posts the design files for a "cycloidic" > reduction drive that is very simple to make even in a home shop, And > at the same time electric motors from "drones" are so light and > powerful, that if you place a propeller on the motor shaft the > electric motor can lift 3X its own weigh hundreds of feet into the > air. Motor like this come at every price pint starting at about $5, > going up to about $60. These are very high performance motors for > cheap. > > Combine the high-reduction cycloidic drive with a small low cost BLDC > motor and you have a point for a robot arm (or leg) or a machine tool > axis. Here is a model of one of these motor and all -- please try the > "explode" button to see the insides of the drive. (The button turns > the drawing into a parts diagram) https://a360.co/2KhamaI > crashes my version of firefox. And why the heck does firefox so helpfully prepare a crash report it cannot submit. Dumb isn't an adequately descriptive word. Twice, I thought the first time was a fluke. Wasn't.
> OK back to real-time... > > If these joints can be mades for not a huge amount of money then it is > affordable to build a robot using 20 such joints. This would get is a > basic quadruped animal, like a small dog. But now we have a 20 axis > machine to control and it can't be pre-programed. I am looking at > using one computer per joint -- that is 20 of them. Each one being > small enough to fit INSIDE the joint housing. These computers are > doing a very hard RT job. The MOSFET gates are driven by a pin from > the processor and we commutate the BLDC motor in software. Switching > coils on and off as the motor spins. Amazing what you can do when a > 100 MHz 32-bit computer costs $2. and can fit inside a 25mm square > aluminum tube. > > No plans to do this soon, the first step is to finish the CNC > mini-mill conversion, then a single axis prototype. If it does not > work out I will use the motors for a drone. There seem to be a > number of people working on this > > On Sun, Jun 24, 2018 at 2:42 AM Nicklas Karlsson < > > nicklas.karlsso...@gmail.com> wrote: > > On Sat, 23 Jun 2018 21:04:48 -0700 > > > > "John Dammeyer" <jo...@autoartisans.com> wrote: > > > But we are still talking about a Multi-Tasking, Round Robin > > > Priority > > > > Driven > > > > > OS right? Like 3 tasks with the same priority are time sliced > > > with equal processing time? ... > > > > Ordinary real time scheduling with EDF as first choice which I never > > had access to or rate rate-monotonic as second choice is what I > > prefer then periodicity/priority is different and round robin for > > equal priority. > > > > I think an excellent example of a "hard" although not neccessary > > critical real time process is to read data from some kind of serial > > receive buffer. If dead line is set to buffer full and trigger then > > half full I think this example will fit perfectly with the theory. > > In case hardware to trigger real time process, usually an interrupt > > and pirority is available theory will fit with practical > > implementation. > > > > > Inter task communication done with pipes. A task can > > > suspend on a pipe until it's written to by another one. ... > > > > Round robin could be implemented with function calls and usual > > parameter passing. For round robin any shared memory area will also > > work. In an operating system this may be implemented as a list there > > functions which should be called are stored. > > > > Different prioriority there tasks can interrupt each other is there > > semaphores, mutexes, message passing in some form is needed. Could > > in some cases be implemented with a shared memory area and write one > > in a shared memory area to indicate then new data is available. > > > > > > Nicklas Karlsson > > > > > > -------------------------------------------------------------------- > >---------- Check out the vibrant tech community on one of the world's > > most engaging tech sites, Slashdot.org! http://sdm.link/slashdot > > _______________________________________________ > > Emc-users mailing list > > Emc-users@lists.sourceforge.net > > https://lists.sourceforge.net/lists/listinfo/emc-users -- Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Genes Web page <http://geneslinuxbox.net:6309/gene> ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
