On Sun, May 22, 2016 at 12:44 PM, Gene Heskett <ghesk...@wdtv.com> wrote: > > On Sunday 22 May 2016 14:28:02 Jon Elson wrote:
No, not a PCI bus or a special purpose card. The way it will be is some high speed serial bus like SPI or the like and in place of the PCI card a generic micro controller card such as maybe even a Pi or Arduino but NOT running an operating system. The OS and it's scheduling is the source of jitter. These bare micro controller cards are now under $10 and can take the place of a 5i25. As an example I use an Arduino Nano to drive the steppers in a robot. The Nano is 1/2 the size of a business card and cost under $4. The card connects either steppers or DC brushed motors with built-in encoders and takes commands for speed and position. I can drive only two motors but at $3.50 each I can afford more than one Nano. The Nano does not have an OS and at best can do cooperative multitasking. But these small micros have built-in hardware counters that run off a crystal controlled clock and I can program the counters to do hardware based pulses while at the same time running a PID loop at 100Hz. My rule is to NOT try to attempt rocket science on an AVR chip, just do one real-tine loop and leave the smarter stuff to the "bigger" Pi 2 and leave the really smatter stuff (autonomous multi-vehicle navigation) to the multi-core desktop machine The above is actually kind of crude and slow. A better approaches to make use of the ARM's "PRU". Some version of ARM have two additional micro controllers on the main chip. These are special purpose real-time processors that run independent of the main ARM cores. They are for running time critical code that can not be run under a multi-tasking OS. When you buy, for example a BBB (Beal Bone Black) you get a multi-core computer that can run Linux. But in addition you have two PRUs. Each PRU is a 32-bit micro controller with it's own RAM to hold it's own software. These can do anything you'd like them to and run independently of Linux. They could do the job of a 5i25 board. Some more detail here: http://processors.wiki.ti.com/index.php/Programmable_Realtime_Unit_Subsystem Advantages: Nothing to buy or add on. It is already on-chip Disadvantages: This is only on TI parts as far as I know, you'd need to learn how to program and debug PRU code. PRU is a completely different architecture from ARM. We call this asymmetric multi processing. This is where there are multiple CPU cores but some core are not identical. It is not a new idea as it was used in some 1960's vintage mainframe computers for this same purpose, to control devices that needed exact timing like disk and tape drive and printers and network interfaces and the like. On the old CDC 6400 mainframe all the I/O was done by these little computers while user level software ran on the bigger CPUs. IBM mainframes had a simpler version of this call Channels but the idea was to move the real-time stuff off the main CPU and out of the kernel of the OS. TI's ARM cores do this with PRUs The future I think is going to not be any of this. Motors will become smarter like the Dynamical servo motor. Dynamical motors accept serial commands for position and speed and have built-in micro controllers. You can send an acceleration curve to the built-in controller or change the PID constants and the motor just does what is commanded. In time this idea will move out of it's current limited use and into mainstream industry. > > However, they will have truly arrived when they grow a PCI bus, and a > card such as the 5i25 is used to offload the timing difficult tasks such > as stepper generation and encoder resolving, to the 5i25. At that point > it can compete, but it won't happen until something like that (Mesa 5i25 > clone) does become available to the ARM stuff. But it will not be any > cheaper when that happens as the pci version is still $90, which has to > be added to the cost of the ARM board itself. > > But I've not tracked whats available since the ARM crew was shown the > door about 2 years back. Sure I could sub to their list too, but I > thought it was nice to be informed of cnc progress, state of the art, > from one list while the genesis stages of the BBB were being done and > reported here... > > Cheers, Gene Heskett > -- > "There are four boxes to be used in defense of liberty: > soap, ballot, jury, and ammo. Please use in that order." > -Ed Howdershelt (Author) > Genes Web page <http://geneslinuxbox.net:6309/gene> > > ------------------------------------------------------------------------------ > Mobile security can be enabling, not merely restricting. Employees who > bring their own devices (BYOD) to work are irked by the imposition of MDM > restrictions. Mobile Device Manager Plus allows you to control only the > apps on BYO-devices by containerizing them, leaving personal data untouched! > https://ad.doubleclick.net/ddm/clk/304595813;131938128;j > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users -- Chris Albertson Redondo Beach, California ------------------------------------------------------------------------------ Mobile security can be enabling, not merely restricting. Employees who bring their own devices (BYOD) to work are irked by the imposition of MDM restrictions. Mobile Device Manager Plus allows you to control only the apps on BYO-devices by containerizing them, leaving personal data untouched! https://ad.doubleclick.net/ddm/clk/304595813;131938128;j _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
