Kirk Wallace wrote: > Wasn't there some talk, last year, about real-time Ethernet? Ethernet, > to my uneducated brain, seems much more appealing than USB. > Jan Kiszka did this for RT Linux (its called rtnet), and it is apparently a complete project, and is being maintained. BUT, the slave side is NOT done. That's the problem. If you wanted to have some slave motion control devices that were commanded by the EMC system using rtnet, you'd have to do some tricky stuff, at the least, to make them perform the way rtnet requires. Basically, time slots are allocated based on the number of devices and their requirements for data transfers. Then, the master sends out sync packets every interval, and all the slaves have a time relative to the sync that they may respond in, and at no other time. it seems like many of the really nice, cheap and flexible Ethernet-enabled chip products, such as the many Arm-based micros with USB and net ports, may not be flexible enough to bend their Ethernet ports to work with rtnet. Too much of the protocol is handled in hardware to adapt to rtnet, or at least that is the impression I got while diging through a number of data sheets. Maybe there is a way to do it, but the off the shelf protocol stacks that have been written for these micros certainly won't work without massive changes, if at all. > Another thought, is that as long as there are desktop PC's, there will > be slots (maybe?) and for real-time, a slot card controller would be the > most efficient. I guess this doesn't address the bare-bones systems were > cost and simplicity are the major issues. So far, there have always been > parallel port cards to fit the latest slots, so maybe it's not yet worth > worrying about? > > I haven't tried a PCIe parallel port card yet, as I don't have a PC with PCIe slots, yet. But, that definitely SHOULD work. If a PCI parallel port works, a PCIe should, too. > I wonder if there will be a time when EMC2 will need to branch, to cater > to different system types? How long will those, that want to do the most > with the least, and those that want to do the most with the most, be > able to use the same EMC? > > EMC is already a very flexible system, that can do both servo and software-generated steps, and even mix them in the same system! Robots and hexapods, too. Why branch?
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