raspberry pi 3 model b+ support realtime

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19 Mar 2019 14:21 #128972 by mahmoudgad
Hello everyone,
I would like to ask some questions about rasraspberry pi 3 model b+
  • raspberry pi 3 model b+ is found any problem with Latency or real-time
  • if the raspberry pi not good solution for providing real-time app what the alternative?

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20 Mar 2019 13:30 #129055 by pl7i92
raspberry comunication is not that good
only up to 500mm/min at max 5000steps per decond

use a ITX like J1800/1900
M525D

better then all if a real mashine is on the system
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20 Mar 2019 13:46 - 20 Mar 2019 13:48 #129065 by andypugh

mahmoudgad wrote:

  • raspberry pi 3 model b+ is found any problem with Latency or real-time

  • It has usable realtime performance, but there isn't a very good selection of interface hardware.

    The GPIO pins can be used, but encoder counting and step generation have to be done in software (like a parallel port system)
    There is a driver (hal_gpio) but I don't see it in the LinuxCNC source tree, just in the Wiki.

    There is some oddly laid-out info here. wiki.linuxcnc.org/cgi-bin/wiki.pl?RPi3BPreemptRT

    The other option is to use the SPI bus and the Mesa 7i90 . Support for that is included in LinuxCNC
    Last edit: 20 Mar 2019 13:48 by andypugh.
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    20 Mar 2019 20:38 #129109 by tommylight

    mahmoudgad wrote:

  • if the raspberry pi not good solution for providing real-time app what the alternative?
  • A normal 3 to 10 year old PC with parallel port will do just fine.
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    20 Mar 2019 20:43 #129110 by PCW

    The other option is to use the SPI bus and the Mesa 7i90 . Support for that is included in LinuxCNC


    Also the 7C80 and 7C81 which are a mechanical match to the RPI
    (and should be available towards the end of April)
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    02 May 2019 18:39 #132554 by stevedw
    Any update on these(7C80)? I'm not yet seeing them in the various stores selling Mesa boards.

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    27 Jun 2019 19:41 #138022 by AgentWD40
    *bump* for the previous question. I see the 7c81 is in the store, but not the 7c80.

    Can the rpi run the ethernet mesa cards like the 7i76e and 7i96?

    Finally and most importantly, thoughts on the new rpi 4 with linuxcnc/mesa?

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    27 Jun 2019 19:47 - 27 Jun 2019 19:47 #138024 by andypugh
    The Pi3 does not work with Ethernet Mesa cards as the ethernet is on the USB bus.

    But: It seems that this is not the case with the Pi4. So there is more chance of that working.

    The raspian_stretch_full.gz file here is supposedly a pre-installed LinuxCNC image for the Pi3B+. I haven't tried it myself (I was going to do the same thing, but got beaten to it)

    geneslinuxbox.net:6309/gene/Genes-os9-st...ebian-stretch-armhf/
    Last edit: 27 Jun 2019 19:47 by andypugh.
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    03 Aug 2019 22:32 - 03 Aug 2019 23:42 #141302 by spma
    Hi everyone!
    I just want to leave my experience here because I've been able to successfully use an Pi3b+ with a Mesa 7i92 + 7i77 + 7i84 boards.
    It was implemented on a Pinacho Lathe with servo motors and controls everything (including PLC logic) with a servo_thread of 2.5ms.
    It controls 2 axis + Spindle + 2 MPG hand weels + Spindle Gearbox (3 gears) + ATC Turret + control panel with basic buttons and analog signals to control the feed bars on Gmoccapy.
    (LinuxCNC v2.7.14)

    Regarding the Pi4 stuff, I'm currently building a PREEMPT-RT kernel on mine to start testing it out, so I'll post updates about it in the Pi4 topic.
    Last edit: 03 Aug 2019 23:42 by spma.
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    05 Aug 2019 02:35 #141390 by Bari
    Rpi4 already working with LCNC:

    forum.linuxcnc.org/18-computer/36879-raspberry-pi-4?start=0

    Two mesa boards already tested and working over SPI and Ethernet.

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