On 02/02/2016 02:59 PM, andy pugh wrote: > On 2 February 2016 at 22:45, Peter C. Wallace <p...@mesanet.com> wrote: >> This might be true with parallel port software stepping systems that require >> a >> high speed base thread for pulse generation and perhaps encoder counting, >> but is not the case at all for servo thread only systems, >
Parallel port is a monkey business. It was never meant to be used as such. I know, it started as a cheap IO for simple installations but that's not a viable solution now with FPG based interfaces such as Mesa cards, USB3.x, etc. > I don't think that it is necessarily the case even with parport-only > systems. There seems to be an obsession with getting super-low latency > and a concomitant belief that unless you can get into single-digit > microseconds you might as well give up. Yes, this "obsession with low latency" is a concern that comes up on this mailing list every once in a while. PC architecture is not the best for handling RT, however, most CNC should not depend on millisecond latencies on generic motherboards. That should be handled by the interface/controller independently from programs running in user space. It makes no sense to me to use modern motherboard and enable only one CPU core out many to ensure RT and low latency. For example, Digital minicomputers were much slower compared to PC motherboards, yet they were able to handle industrial applications just fine. Application ran in RT OS to handle DIO or analog signals. Old PDP HW is getting replaced with special PC cards that are able to run original software while generic Windows runs on the PC. No latency issues. Same should be possible with LinuxCNC IMO. > In practice few stepper systems have hardware that can follow even a > 50uS base-thread. I spend a lot of time on the forum saying "Stop > fiddling, it's fine as it is, get on with something productive" > Agree. 3D printing world is growing precisely because of dedicated SBCs built with low cost microcontrollers and motor drivers. They handle everything including UI for selecting files from tiny memory cards. Large CNC systems require more computing power of course, but that too should not be a problem for decent IO cards independent of motherboard latency. -- Rafael ------------------------------------------------------------------------------ Site24x7 APM Insight: Get Deep Visibility into Application Performance APM + Mobile APM + RUM: Monitor 3 App instances at just $35/Month Monitor end-to-end web transactions and take corrective actions now Troubleshoot faster and improve end-user experience. Signup Now! http://pubads.g.doubleclick.net/gampad/clk?id=267308311&iu=/4140 _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
