On Friday 24 January 2020 00:45:17 John Dammeyer wrote: > Comments between. > > > -----Original Message----- > > From: bari [mailto:bari00...@gmail.com] > > The guy down the hall from me has been keeping RTAI alive for LCNC > > the past few years. I'm not sure if real time performance would be > > much better using QNX vs Linux + RTAI on a PC. > > I think one first has to define exactly what needs to be real time. I > doubt QNX is free. > > > http://blackberry.qnx.com/en/software-solutions/embedded- > > software/industrial/qnx-nuetrino-rtos > > > > There would be trade-offs on hardware support to port LCNC to QNX, > > especially when it comes to GPU acceleration. RTAI and preempt_rt > > perform pretty well on many low cost PC's with base threads down in > > the few microseconds range for software stepping. > > One of the reasons to use Linux or Windows is that as the motherboards > (CPUs) change from one core to 2 cores to 8 cores to 1 core with two > peripheral processors etc. the basic work to make the system has been > done. When you plug in that USB WiFi dongle it's usually possible to > find a driver. Same with a parallel port card or camera card or a > second Ethernet card > > If you are using Ethernet and UDP then it's a launch and forget method > on a private Ethernet. Or if TCP/IP then reliable ordered messaging. > So the workhorse for screen and outside world communications is there. > > > Going with a motion controller where the real time control is closer > > to the motors give us what? I still need a GUI on some display at > > least 12" across. A smartphone display might be OK for a CNC glue > > gun but not to control my 2 ton+ VMC or lathe. > > And there's the rub. In the past, connecting all the > encoder/resolvers and motor input into a PCI card and having the PC do > all the work made sense. Especially since the only other option was > an 8 or maybe 16 bit processor that used EPROMs. (I'm talking 1990's > here). > > > The ~$2 STM32 boards gives you an ARM processor with unprotected IO. > > You need many more parts around that to buffer, level shift and ESD > > suppress. > > This will be true for anything regardless of where the I/O begins. > Note the MESA cards have buffers.
Not all, the 7i90 being a rather glaring exception, it's cheap for it capabilities but needs another $135 in 7i42TA's to protect it. I suspect that any of the Mesa cards that output via 50 pin scsi connectors have similar restrictions. > The Xylotex Cape for the Beagle has > buffers. The question to ask or answer is where do you want that to > be. At one point it was on the PC motherboard and came out as a > DB-25. Thousands of machines still run with that interface. At the > moment mine does. > > I really don't know what is going on under the covers for either the > MESA Ethernet 7i92H or the Ethernet Smooth Stepper for MACH. But > considering the power of the processors running machines back in the > 90's or early 2000's and that the mechanics for the metal cutting > haven't changed much, my guess is that some 32 bit processor _not_ > running Linux so that the graphics/USB/etc. doesn't cripple the real > time behaviour will be the solution. > > For example a PIC32 with USB (for firmware upgrades) and Ethernet (for > Control) along with a CAN bus (CANopen control of non-real time > peripherals) and the Free RTOS could be the building block. The > software on the PC written in say Lazarus (Object Pascal, write once, > compile anywhere) which is available free with graphical capabilities > on machine for Linux (PCs and Pi and Beaglebone) , Windows and MACs. > > This approach doesn't get mentioned. A small 32 bit processor like > this could even have a small LCD display with a few buttons for basic > machine operation. Enough to move axis, turn on/off spindle etc. > Simple switch with local/remote mode. I look at the world this way > because that's the type of stuff I've been designing and writing > software for over the last 25 years or so. > > If I understand the Hardware Abstraction Layer correctly this is, in > effect, already being done on the LinuxCNC PC. But when I run the > stress test on my PC the machine has some pretty long latencies. But > it's not needed. > > IMHO > John Dammeyer > > > On 1/23/20 12:17 PM, Chris Albertson wrote: > > > The trouble with the Mesa FPGA design is that it depends on a > > > computer > > > > with > > > > > good real-time performance. It can generate steps but I don't > > > thing you can run a position or velocity PID control loop on the > > > FPGA. > > > > > > You asked about "my controler". No this is not my idea, this is > > > how most current designs work today. You "push" the real-time > > > control down stram > > > > as > > > > > close to the physical motor as possible. In the old days > > > computers where expensive and you wanted to minimize their number > > > but tocay a 32- > > > > bit > > > > > computer with floating point math, RAM and quita a lot of > > > peripheral hardware cost as littel as $1. I buy these $3 PCBs > > > for controlling up to two servo motors with quadarue feedback 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) If we desire respect for the law, we must first make the law respectable. - Louis D. Brandeis Genes Web page <http://geneslinuxbox.net:6309/gene> _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
