Ray Henry wrote: > http://www.ce.utwente.nl/rtweb/publications/MSc2004/pdf-files/011CE2004_Buit.pdf > > An interesting study of RTnet. In it they say; > > "RTnet communication times are mostly determined by the > hardware. Not only processor speed but also architecture and > type of network interface card (NIC) are of great importance. > > That's a bit disturbing isn't it?
I'm following this and other related threads closely. Having experience with computers including PCs since XT times I was disappointed on more than one occasion seeing interfaces being (ab)used for other than their intended use. Parallel port was definitely in that category because of it's price but that's history now. If I were asked to select the most common port, bus, or interface in PC for use in RT environment I would say either floppy or ATA bus. They are present on most motherboards. However, they are now practically obsolete and bad candidates for future EMC direction IMO. What's left for RT interface on the common motherboard are PCI and SATA buses. SATA seem to be the most suitable for RT use because it's on all motherboards and it already handles mechanical devices directly with rich command protocol. Let's compare SATA and Ethernet and the complexity of using either one for "direct CNC." Case 1, Ethernet-CNC: To implement Ethernet-CNC we have to have a working motherboard/Linux drivers combo, Ethernet/CNC adapter, and special Ethernet driver. That's one port, two different drivers, one of which will always depend on Ethernet chip architecture which changes a lot, and Ethernet to CNC adapter (DIO, etc.) in order to communicate with CNC machine. Two sets of chip/drivers needed. Case 2, SATA-CNC: Implementation requires motherboard/Linux drivers combo with SATA (always available), SATA/CNC adapter, and SATA-CNC driver. Once Linux boots up, we know that the driver for (S)ATA bus is OK. If we have a generic SATA-CNC driver that piggybacks on generic SATA driver, we should be able to talk to CNC device also. One set of chip/driver combo to get CNC working. SATA speeds should be sufficient to handle some of the most demanding RT jobs for hobby and small business use. (S)ATA is most likely going to be easier to support as there is a limited number of chip sets in production. Key EMC developers already know (recommend) how to select the right MBs for EMC use so it would be only a matter of adding verification for EMC. Case 3, special PCI cards: That stays the same as we have it today for high end use. Question is do we benefit with using SATA-CNC protocol for example when we need special SATA-CNC adapter for connection to the outside world? SATA is no worse than Ethernet-CNC which too requires a special adapter for connection to CNC machines. Perhaps low cost PATA to SATA converters could be used for the simplest connections to the outside world. SATA protocol is well known and could possibly be adapted for use with CNC I believe. Once created, "SATA CNC driver" would work on all motherboards and possibly PCI/SATA cards with known latency limitations of course. SATA is more vendor neutral than Ethernet which has no protocol of it's own on the motherboard side. Architecture with a set of registers for SATA is defined while for the Ethernet is not. There is almost always a spare (S)ATA port on the motherboard, but only one Ethernet port which would better be used for default network connections. Good signaling characteristics, 32-bit CRC, DMA, point-point connection, and hot plugging make SATA well suited for CNC IMO. Cable is limited to 1m but that's enough to connect to CNC adapter boards externally. There is already a list of more or less suitable motherboards for RT use with EMC. It's possible that they would be most suitable for use with SATA-CNC as a main interface to the outside world. http://www.sata-io.org/esata.asp http://www.interfacebus.com/Design_Connector_Serial_ATA.html No matter which protocol is going to be used, adaptive electronics will need to be built but that won't be as easy as the one used for PPorts. The question is, which would be easier, SATA-CNC or Ethernet-CNC? My guess is SATA. -- Rafael ------------------------------------------------------------------------------ SF.Net email is Sponsored by MIX09, March 18-20, 2009 in Las Vegas, Nevada. The future of the web can't happen without you. Join us at MIX09 to help pave the way to the Next Web now. Learn more and register at http://ad.doubleclick.net/clk;208669438;13503038;i?http://2009.visitmix.com/ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
