On Thursday 11 April 2019 15:41:15 Chris Albertson wrote: > I have to agree, The entire point of moving al real time functions > to hardware is so that a real-time OS is no longer required. > > The only reason Linux is even needed is that it is an easy way to get > a real-time OS. If not for the RT requirement you could use a Mac or > Windows or even an iPad or any cell phone. > > If the machine controler could run on a me=aintstream OS (like Windows > 10) and on a normal notebook PC it would be orders of magnitude more > popular and widly used > > "EMC" as it was called (then later Linux CNC and then MK) was a great > idea: Use existing, low cost off the shelf hardware to control a CNC > machine. This is still a good a very idea but today the existing > low-cost hardware looks like an STM32 chip and cost about $5. These > chips have "compute power" roughly the same as the old PCs EMC was > developed with. These little chips are nice to use not just because > of the price but because there typically come with an RT operating > system (based on CMSIS) that has much better RT performance than any > RT-Linux. > Even th D-525-MW motherboard? I can latency-test for an hour or 2 on this machine I'm building up right now, and not show any worse than 5.1 microseconds for base thread latency, and If I run without that thread, which I don't use anyway, and the worst case latency is 4850ns. Thats right alongside the figures I've seen quoted for the STM-32.
> There is nothing special about Linux other than it provided a cheap > and easy to get RT OS. And security. Windows may be improving, but connected directly to the net, how long before its owned. I went from amiga to linux in 1998, and have not been touched since. That of course includes using another linux product, dd-wrt, between my local network, and the network at large on the other side of my cable modem. > The CMSIS based RTOSes on STM32 are better. > I have some experience with both ways and believe by moving to the > smaller RT system is nearly Arduino-like simplicity and ease of use. > I'm using it for robotic motion control now. > > On Thu, Apr 11, 2019 at 3:32 AM Les Newell <les.new...@fastmail.co.uk> > > wrote: > > > Actually I *don't* want to run a form of Linux. > > > > I suggested running a Linux variant because it would simplify > > porting code. Most HAL code only uses a few system calls so you > > could emulate those calls. IMHO rewriting everything to run on > > dedicated hardware is a bad idea. Not having compatibility with the > > main LinuxCNC code base will mean you have to maintain all of the > > code by yourself. That is a lot of work. > > > > > Since it's dedicated > > > HW, the tasks can be hardcoded for bare metal and stored in flash > > > and directly load the STEP/DIR pins with SPI data which does > > > precise, synchronized step-outs.. This is leaner, simpler, more > > > reliable and the latency can be very low and consistent (although > > > LinuxCNC on Preempt-RT is already all of that for my machine). > > > > If you are just concerned with accurate steps then just move step > > generation to external hardware. The trajectory planning etc is done > > at a relatively low speed (usually 1ms intervals) and even a few > > hundred microseconds of jitter isn't a big deal so there is nothing > > much to gain in moving this to dedicated hardware. The Ethernet Mesa > > boards work this way. They use hardware step generation that is > > updated every 1ms over Ethernet. > > > > > This would require somewhat extensive modification of code. > > > Microcontrollers typically use C and cannot handle C++'s OOP nor > > > dynamic memory allocation. > > > > This is a myth. Even the lowly 8 bit ATMEGA series is fine running > > OOP C++. Look at Arduino. The majority of that code is C++. Several > > years ago I wrote a preemptive+cooperative multi tasking real time > > OS in C++ and it ran well on an ATMEGA. On more memory restricted > > parts you need to be careful with dynamic memory allocation but it > > still works as long as you don't go overboard. If you're considering > > moving emcmot etc to another processor you're gonna need something > > with considerably more grunt than an ATMEGA anyway. > > > > Les 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> _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
