Rafael writes: > On 06/05/2015 01:18 AM, Alexander Rössler wrote: >> >> Rafael writes: >> >>> On 06/04/2015 07:13 AM, Ron Bean wrote: >>>>> If you need one computer to see the GUI and one for realtime >>>>> effects, why not just start out with a real computer and load Linux and >>>>> LinuxCNC on it? >>> > .... snip > >>> In my HW support experience I came across PDP-11 systems running in >>> steel mills, nuclear and hydro power plants, factories, etc. with little >>> or no graphics. Most used VT100, some used more advanced color >>> terminals. Systems with 32kW(ord) or 64kW RAM controlled huge machinery >>> with RTOS on much slower CPU than we have today. >> The future are distributed systems. Distributed setups are industrial >> standard and are used everywhere from automotive to automation >> industry. CAN and Ethernet are used these days to distribute > > neither one is suitable for strict real time. CAN as event triggered bus is not. You may understand TCP/IP as Ethernet. However, Ethernet can be used as time-triggered bus too. There are many standards such as EtherCAT and Powerlink which are widely used in automation industry.
> >> functionality across different ECUs. The BBB is fine when it comes to >> CAN but an even stronger platform from TI is coming up: the BeagleBoard >> X15 with Gigabit Ethernet support > > Don't mix computer BUS and cabling. Two different things. Some cables do > act as traditional extend bus but none at the length of an airplane or > HMMVE. > > What good is Gigabit Ethernet when you need to connect a keypad, a > switch, accelerometer, or optical sensor to BBB? Ethernet is not a bus, > it's one of communications peripherals. You are wrong, Ethernet is a bus. When you take a look at the history you will see that it started out with a very different physical interface as nowadays. The huge advantage of Ethernet is that network hardware is cheap (not all is RT compatible though) because it acts only on the data-link layer (Ethernet frames). What I am talking about are Ethernet hubs. The idea of time-triggered buses is to resend that every cycle. Therefore, a higher network bandwidth means that one can use a smaller cycle time. The bandwidth is not wasted as some people stated. Why not attaching the sensors you mentioned directly to the BBB? Just create (or use one of the many) capes with a decent connector and you are fine. If you want to go the industrial standard way you can buy sensors with bus interface (I am not talking about I2C, SPI, ...). Onewire is common for simple sensors. Another example in the automotive industry it is pretty common to have ECUs that do only simple tasks like reading out sensors and providing the data on a CAN bus. With microprocessors getting cheaper and cheaper the industry will further move into distributed systems. > >> On the other edge of the spectrum we have another low cost solution that >> is currently funded on kickstarter C.H.I.P. a 9$ dollar Linux computer >> with Bluetooth and WLAN => a cheap solution to connect sensors. > > This is one of a kind toys that don't make a standard! Nor would anybody > serious use it for a CNC machine. > >> I even heard about things like fly-by-wireless. Which boils down to >> removing the wired buses inside a plane. So face the facts: Big >> monolithic computer setups will soon be banned to server farms. > > Most airplanes and modern military vehicles use computers based on > decades of developments on VME bus and it's derivatives because they > need a lot of connections. That likely includes CompactPCI, it's > emerging CompactPCI Serial, and VPX. > > As tiny lasers are getting cheaper, cost of building optical bus and > compatible peripherals will become more common in the near future so > we'll see even more data buses. Optical cables have different problems than metal cables. They have more problems when it comes to mechanical stress. I am not sure they will succeed copper wires that quickly. When you take a look inside an airplane you will see that the wiring is consuming a lot of space inside the hull. The idea of replacing some buses with wireless interfaces drastically reduces development costs. So maybe in 30-50 years we will have wireless operating planes. > > Every computer in existence has a bus, available or not, for connections > to additional peripherals. There is a bus on BBB, RaspberryPi, Radxa, > and other little SBCs to add peripherals. My comment was about the > problem with every little SBC having different connectors and their > positions on the board while all are using "sandwich mechanical > architecture" that cannot be expanded easily. What you are pointing out is that these devices do not come with standard connectors. There are some capes (additional board that can be put on the pin headers) that provide different connectors for different applications. The BeagleBone Green will come with connectors for the Groove sensors if you want something out of the box. Furthermore, you have USB and Ethernet connectors available. However, I agree that connectors are a big problem in general when it comes to computers. Only few capes address this problem an come with pin headers to connect sensors/motors. However, that is one problem we tried to address with the SandyBox and the different controller boxes (Lin-Ctrl stepper driver, Print-Ctrl for the 3D printer) . They come with standard Molex connectors to connect sensors, switches an motors. We are planning a future version of the SandyBox to address this problem. So if you have ideas please share them. > > Based on what I've seen at Embedded computers trade show this year I can > easily say that "computer data bus" won't go away any time soon. PCIe, > VME, VPX, CompactPCI, PC104 and on and on. Companies are clearly > commiting to support for advanced buses for the next 20 years or more. The application for PCIe and co is clearly high performance computing. This is whole different application than what embedded systems try to solve. Btw. there is Raspberry Pi model with a PCB-style connector available. > >>>> and a PCI slot for a GPU. Another solution might be something like a BBB >>>> that plugs into a PCI slot in a generic PC. Either one eliminates the >>>> USB connection, which is the real problem. >>> >>> Good idea assuming there would be a volume to keep the costs down. >>> >>> IMO it would be better if ARM architecture based universal bus would >>> emerge for use in small embedded systems under $100 so that vendors >>> would be encouraged to build controllers with "Mesa card" like >>> functionality and other interfaces to handle digital and analog IO >>> connections. >>> >>> This thread brought up interesting ideas and comments; good starting >>> point for a "kickstart" project ;-) >> -- Alexander ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
