On Monday 09 October 2017 12:57:45 Nicklas Karlsson wrote: > On Mon, 9 Oct 2017 12:36:20 -0400 > > Gene Heskett <ghesk...@shentel.net> wrote: > > On Monday 09 October 2017 11:45:58 Nicklas Karlsson wrote: > > > > > There ARM M is tiny and dirt cheap and is very good for > > > > > real-time work. I have a robot with four motors and encoders > > > > > and get 44,000 interrupts per second > > > > > and much better real time latencies then from any Linux based > > > > > solution on any platform. > > > > > > > > > > My solution for robot control is a hierarchy with ARM M for > > > > > the lowest level, then > > > > > Raspberry Pi 3 connected by high speed serial. > > > > > > Right now I am at this point with high speed serial communication > > > to ARM for the lowest level. > > > > > > > I did succeed in building a fully rt-preempt 4.9 kernel on it > > > > today, took about 4 hours, but I've not yet attempted to boot it > > > > as I saw some stuff go by during the build (when I wasn't > > > > checking my eyelids for leaks :) that I yet need to turn off. I > > > > think, other than fine tuning the kernel build, that convincing > > > > the hm2_rpspi driver that it should run on the rock's rk3328, > > > > arm64 quad core SoC, running at up to 1.5GHz should be the last > > > > major hurdle to making linuxcnc run on it, ... > > > > > > Happen to know how many SPI ports there may be? > > > > This driver that Bertho Stultans wrote, can do 5. Over 2 pin groups > > IIRC. However since I was the lab rat, only the SPI1 set has been > > extensively tested. > > There is hardware support for 5 SPI ports, or? > > > the "rates" are the write, and read, clock rates, corresponding IIRC > > to a 41 megabaud write to the 7i90 rate, and a slower 25 megabaud > > rate for reading back the data from the 7i90. > > I figured around 100kbit/s full duplex is what is needed per axis, it > should be possible to squeeze into a 1Mbit/s CAN network but it's at > the limit. UART would work but setting baud rate for speeds above > 1Mbit/s might have accuracy problem. 5-10Mbit/s SPI give me about 5-10 > times more bandwidth than needed. > However, bear in mind that the pi isn't using any PID's, so long turnaround times expand the perceived by the software, following errors because LCNC is reading the data back to determine if its following orders, and a long turnaround delay means the data is stale. I have those errors set a bit looser, but only in Z case have I allowed more than a thousandth of an inch. X axis: FERROR = 0.0010 MIN_FERROR = 0.00020 Z axis: FERROR = 0.020 MIN_FERROR = 0.01
That last I am sure is a leftover from when I was having an interface problem. So I just reset that to match X, and had no problems homing it for 3 startups, so I believe that problem is solved. That I have dissed the thrust bearing and shimmed it to get rid of around 20 thou of end play also helped, leaving me with a 3 thou backlash setting. Less than that, I'd have to restuff the nut with bigger balls. Thats been done to the X nut, but its mounting has some give, so its running a .00475" backlash. It stays at about .002" if I can ever get the final squeeze on the homemade felt swarf wipers, that s/b be good for years. > > Both of those rates could probably be improved with stronger, as in > > faster rise and fall times in the pi's pin drivers, they are a tad > > puny. > > Delay is a problem for the signal coming back. > > > The interconnect cable between the pi and the 7i90 is only about an > > inch long ... > > No need for driver here, in these cases SPI make sense, fast and > cheap. > > > > Regards Nicklas Karlsson > > ---------------------------------------------------------------------- >-------- Check out the vibrant tech community on one of the world's > most engaging tech sites, Slashdot.org! http://sdm.link/slashdot > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users 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> ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
