What should be the roll of LinuxCNC going forward? Regards Stuart
On Fri, Jan 24, 2020, 1:18 PM John Dammeyer <jo...@autoartisans.com> wrote: > Hi Jon, > > -----Original Message----- > > From: Jon Elson [mailto:el...@pico-systems.com] > > > > On 01/23/2020 11:45 PM, John Dammeyer wrote: > > > I really don't know what is going on under the covers for > > > either the MESA Ethernet 7i92H or the Ethernet Smooth > > > Stepper for MACH. But considering the power of the > > > processors running machines back in the 90's or early > > > 2000's and that the mechanics for the metal cutting > > > haven't changed much, my guess is that some 32 bit > > > processor _not_ running Linux so that the > > > graphics/USB/etc. doesn't cripple the real time behaviour > > > will be the solution. > > You keep going around and around saying that LinuxCNC > > doesn't work. Thousands of people are using it daily, and > > know it DOES work! If you want to do software stepping, how > > about Machinekit on the Beagle Bone, using the PRU > > to do the step generation? This works amazingly well, and > > costs about $145 plus keyboard, mouse and LCD screen. > > Or, you can network into the Beagle and use some other > > machine for the man-machine interface. > > > > Jon > > I'm _not_ saying LinuxCNC doesn't work. > The opposite in fact and I've run the BBB with the Xylotex cape so I can > attest that it does especially with the dual PRU I/O processors. Even > posted a youtube video on that. > > Where the beagle falls down on the Linux side of things, say compared to a > Pi or a PC, is the video processing just isn't as good. And it shows even > when just running normal Linux compared to normal Linux on a Pi. > > Where my LinuxCNC box falls apart is with the parallel port for stepping > with very high latency issues and that one time warning when LinuxCNC > starts up that I've basically got my motion parameters set too high for the > system. > > The solution is of course the MESA 7 I92H which solves that problem. > > Or when I run MACH3 on WIN-XP with the parallel port with a 65KHz clock > rate. Then that exact same PC doesn't have any high speed step rate > issues. > > Now like the BBB I/O, the PC parallel port is directly coupled to the > processor motherboard and therefore the processor. That LinuxCNC cannot > run the same step rates as the WIN-XP system on identical hardware (dual > boot PC remember) shows that there is some sort of issue with PC hardware > that LinuxCNC is not able to solve. Might well be video drivers. USB > drivers. Network Drivers. Might be how it handles the BIOS parameters. > > Offload that I/O to a USB/Ethernet smooth stepper for MACH or the MESA > 7i92H for LinuxCNC and the latency problems (there are others in Windows) > go away. > > And that, I think, is the point that everyone is making. It's not like > the PC parallel port is used with SPI or I2C on each output pin to expand > I/O. Some of the LinuxCNC solutions involve plugging a board into the PCI > bus and using either co-processors or FPGA (which could have a co-processor > built into them) to handle the heavy lifting. The others involve using > Ethernet and processing outside the box again. > > I agree there are probably thousands if not tens of thousands of LinuxCNC > systems out there running from the parallel port. And odds are they are > running micro-steppers that, if they are lucky, require at most 15kHz to > 18kHz step rates before the stepper motor torque falls off so badly that > they lock up. So the Parallel port version of LinuxCNC has no issues on > those systems. > > But the latency warning for 50khz step rates for the DC Servos under > LinuxCNC that doesn't happen on WIN-XP and MACH3 suggests that I've reached > the upper limit of the LinuxCNC OS and the parallel port with this > particular configuration. > > But as I've been saying, the moment you add some sort of external FPGA or > processor based external card that offloads the heavy processing for high > speed encoder/step/SSERIAL etc. then it's not just LinuxCNC anymore but a > PC dependent on outside hardware. And that's what the subject line and > discussion was about I thought. If the motion control was offloaded to a > separate processor then just about any PC remote or right there can load > G-Code, display tool paths and control the machine. > > Without a PCI plug in card. So we really are talking about Ethernet Based > control; perhaps even WiFi. Now we're back to the question as to why > should it be LinuxCNC when it could be a dedicated processing I/O module > with Ethernet connectivity running an RTOS with pre-emptive scheduling. A > small BoB sized board with a single cable (antenna or Ethernet) out to the > outside world. And with a clearly documented interface the software that > connects to this no longer has to run on a particular PC running a > particular OS. > > I hope that clears it up. > John Dammeyer > > > > > > > > > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
