On Tue, 9 Oct 2012, Ron Ginger wrote: > Date: Tue, 09 Oct 2012 07:52:16 -0400 > From: Ron Ginger <[email protected]> > Reply-To: "Enhanced Machine Controller (EMC)" > <[email protected]> > To: [email protected] > Subject: Re: [Emc-users] Mach on Linux > > On 10/8/2012 10:29 PM, [email protected] wrote: >> have a machine that runs latency tests just fine and then gives me a >> real-time error when I start LCNC. Never really tracked it down because I >> always intended just to move on to a new machine. It can be frustrating. >> I think the era of machines that fail latency peaked when the P4 was new, >> but I'm not really sure about that. I suspect that Mach also runs better >> on machines with low latency and the machines that LCNC complains about >> also don't run Mach as well as they might. It's just that Mach ignores the >> long intervals, mostly because step/dir machines are somewhat immune to >> that issue. >> Eric > > These issues are why I am so strongly in favor of the dedicated > microprocessor for the real time part. It is the norm in all computer > systems- look inside that PC and Ill bet there are a dozen separate > processors doing things like graphics, network, disk control, etc. PCs > are wonderful GUI devices and have great computational ability. They > were never designed to be real time systems. > > Why are some people so hung up on the idea that one box (even a box full > of micros) must be used as the machine control?
Well there are a lot of very good reasons for this: 1. If you do not have a real time OS you have no guarantees that even your buffered step/dir device will not run dry occasionally... 2. By moving part of motion control to a separate (usually proprietary) motion controller you have now created a more complex and limited control system because of buffering and communication delays (note that a lot of the big boys are moving to systems like Ethercat on guess what: real time PCs!) 3. LinuxCNC capabilities extend to all hardware. These capabilites include things that Mach has had trouble with from day one like rigid tapping and proper spindle syncronized threading. If a new feature is added to LinuxCNC, it becomes avalable to everyone from simple parallel port systems to high end dual feedback servo systems. This is not the case if you have to depend on the hardware manufacturer for the added features. You can solve these issues by moving more and more of LinuxCNC to the embedded processsor, but then you need a quite capable processor (and you would also like it to be a fairly stable and open platform) Turns out the the most stable open and inexpensive platform with good floating point performance. At the moment this is a PC. Note that most real time issues are really only for people using random used PCs, there are many new motherboards that have fine real time performance. > > step/dir machines are not immune to timing glitches. My knee mill uses a > stepper on the knee for Z. I had a frequent glitch that lost position. I > replaced the stepper with a BIG servo and had the same problem. I > replaced the parallel port with a smoothstepper and the problem was > solved- I put the stepper back and have never had a lost Z step. > Yes, for windows this is a real problem. > With low cost motion devices like smoothstepper, pokeys, kflop, > centipede, etc it seems clear to me that fighting real time latency > issues on PCs are a waste of effort. > > ron ginger > > ------------------------------------------------------------------------------ > Don't let slow site performance ruin your business. Deploy New Relic APM > Deploy New Relic app performance management and know exactly > what is happening inside your Ruby, Python, PHP, Java, and .NET app > Try New Relic at no cost today and get our sweet Data Nerd shirt too! > http://p.sf.net/sfu/newrelic-dev2dev > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users > Peter Wallace Mesa Electronics (\__/) (='.'=) This is Bunny. Copy and paste bunny into your (")_(") signature to help him gain world domination. ------------------------------------------------------------------------------ Don't let slow site performance ruin your business. Deploy New Relic APM Deploy New Relic app performance management and know exactly what is happening inside your Ruby, Python, PHP, Java, and .NET app Try New Relic at no cost today and get our sweet Data Nerd shirt too! http://p.sf.net/sfu/newrelic-dev2dev _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
