Perhaps it's just semantics but we are not making progress here ;-) On 06/06/2015 05:46 AM, Alexander Rössler wrote: > > 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 Huh???
"BUS" is not event triggered? Every bus I know has an interrupt line(s). Generic BUS is just a data path, not an interface, you are mixing the two. > 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. But that is not a data bus I'm talking about! Using your definition, RS232, parallel port (see, we call it a port), phone line, and traditional CaTV network are also a bus. In my understanding BUS is physical component of a computer to connect numerous peripherals to the CPU and among themselves. DMA for example is used for data transfer between the peripheral and storage (RAM, disk drive, SSD) without CPU intervention. No such thing in ethernet. All these concepts were resolved on mainframes decades ago. What changed is the size of components and their speed. >>> 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 This is becoming silly. Ethernet IS NOT A computer BUS just like USB, RS232, RS485, 60mA current loop, are not traditional data buses. Perhaps the terminology got confused when USB was introduced and you know how much of a bus that is or how real time that can be. I work in large data centers and never hear anybody calling ethernet a bus. In some instances we use Cat-6 cables, in other we use optical for 10Gb or 40Gb connections between the routers, switches and servers. I would never call that cheap. A single ethernet interface costs more than a large box of BBBs. > you will see that it started out with a very different physical > interface as nowadays. The huge advantage of Ethernet is that network I know very well how it started and what kind of connectors were used to connect ethernet interfaces on DEC or other computers over the years. At some point coax cable was used to string PCs together into a network. I probably still have RG-58 cables around, good for amateur radio. If you forgot 50 ohm terminator, or used a cheap BNC connector, that connection went "wireless" and transmitted all over the spectrum except between the computers. I paid my share to that hell but we ever called it an ethernet BUS! > 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. I hear "hardware is cheap" all the time. It is in some instances but when I ask an engineer that demands additional disk space because he thinks hardware is cheap: "if it's cheap, why don't you go out and buy a disk drive?" they walk away and start cleaning their home directories full of "junk" on servers because management tells them to do so. Cost is always relative to age, volumes, and features. > The idea of time-triggered buses is to resend that every resend what? Resending packets to fix broken blocks of data is very costly. Idea is not to resend anything. Send it once and be done with. You cannot afford to lose an interrupt when a mill is at the stop switch. > cycle. Therefore, a higher network bandwidth means that one can use a > smaller cycle time. The bandwidth is not wasted as some people stated. > Ethernet packet is not guaranteed to make it to the other side, speed is not an issue. If you connect only two devices you may get away with it, add a switch and you have completely different scenario. And it gets costly! > Why not attaching the sensors you mentioned directly to the BBB? Just Where I've said that? You still need to connect to a board of some kind, call it shield or whatever. But ... > create (or use one of the many) capes with a decent connector and you > are fine. you seem to completely miss the point. Completely. My original post was related to physical awkwardness of "little computers" with non standard BUS/connectors/protocol. It's possible to build interfaces (shields, capes, or whatever other silly names they come up with) for any computer if you want to go one architecture of a kind but it's costly. You don't need to go further than http://linuxgizmos.com/category/boards/ to see the SBC chaos. Many manufacturers don't want to be compatible with a product from another company. It's similar situation as "Personal Computers" in the 80's. First "personal computers" from DEC were not compatible with HP, IBM, ATT, and bunch of others. Try to find interfaces that you can exchange between "hacker SBCs": http://linuxgizmos.com/vote-now-for-your-favorite-hacker-sbcs-maybe-win-one/ This emerging standard is the closest to what I'm talking about: http://linuxgizmos.com/new-arm-and-x86-com-standard-gets-a-boost/ but the cost is still relatively high. If those who design capes, shields etc. made them for a standard like SMARC you would see more affordable prices for hackers. Just in case, computer data bus is not dead: http://linuxgizmos.com/arm-based-device-developers-get-smarc-coms/ > 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. Again, the discussion was not about what kind of sensors you can buy but interfaces and their physical characteristics in relation to specific SBCs: Arduino, RaspberryPi, etc. Go to Maker Faire and you can see many different "little boards" for all kinds of things but they are mostly not compatible with each other. But they are cheap. >>> 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. I'm working with optical cables on a daily basis for some time now. Again, you don't understand what an optical bus is, it is not a cable, which you seem to mix every time subject of data bus is coming up. Ethernet over optical lines is not a bus. > 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. On my tour at Boeing I learned that wiring is not one of the major problems. Wireless is not magic to solve all of your wiring problems. Radio will never replace wiring in "mission critical systems". Airplane is one of them. Man, that would be simple way to get airplanes off the sky! >> 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. Can you use Arduino ethernet card on BBB? Can you use wireless card from one platform on another? No and that's my problem. > 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. It's here that makes me think that you are involved in SandyBox design or production. Good for you. It's open discussions like this that can make a big difference even though we strayed into computer history, production, etc. I never commented on SandyBox specifically. My comment (again) was related to lack of standards for hobby or DIY makers. That's all. > We are planning a future version of the SandyBox to address this > problem. So if you have ideas please share them. I'm glad to see somebody design a box that serves it's purpose especially if it's able to run Linux. If I understand the description correctly, it's specifically targeting (CNC) systems that use parallel port. There are other options for different CNC machines too many to list them here. -- Rafael ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
