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Modbus TCP

  • Hi
    I have some Onion and wan't to make them Modbus TCP compatible so I can control the gpio from any scada system or some existing aps.
    I installed python light and for installing the pymodbustcp modul i was proposed to instal modbus-pip. BUT i'm running into disk space problem. Has anybody any idea how to proceed?

  • administrators

    you can expand the storage on Omega2 with usb flash drive or micro SD card (omega2+ only)

    refer to this tutorial

  • THX
    I saw that but my intention is to get the pure onion running as ModBusTcp IO module without additional storage.
    Until now I try to find a way to minimize disk space so I'm able to run python-light plus python tcp and GPIO ..

    I found not yet any possibility to free up diskspace, also opgk remove seems to leave a lot of kByte on disk

  • @Mike-Eitel , wich models Omega1 ,2 or 2plus?

    Omega one has a quite big BusyBox, you could tight down that making your own. The omegas 2 & 2plus comes already with a smaler version of Busybox.

    Check out /bin; /sbin; /usr/bin; /usr/sbin; (symlinks -> busybox) to cut down busy box. If you need once a command you did remove just copy a more complete busybox in your /tmp, start it from there and after reboot it is gone again.

  • @Mike-Eitel deleting files (or uninstalling packages) that are present in the original firmware does not free any disk space, but even uses up a tiny bit of it.
    This is because the basic root file system patition is read-only. All changes made by the user are overlaid, and stored on a separate, writable partition, which means: whenever you change a file, a full copy of that file is made and then modified. When you delete a file, a small "delete marker" file is created.

    So you simply cannot free space, only consume it, by using rm or opkg remove.

    The way to go would be building your own LEDE image, and including only the packages you absolutely need into that image.

    It's a bit of a learning curve, and at the moment @onion docs do not provide any information. Maybe this can serve as a starting point.

    But once you get up to speed, building your own images tailored exactly at what you intend to do, feature by feature, package by package, is easy. LEDE has a global config file defining the image to build, and a menu-driven utility to view and edit all possible options.

    What is not easy or even possible at this time is building the official Onion firmware, because there are missing parts onion hasn't published yet. They will probably fill the gaps over time, because they are obliged to.

  • THX Luz

    It's more or less what I feared after testing a little bit. And yes i clearly understand the overlay principle.

    I'm not the deep hacking guy, I do some programming since > 35 years. What I'm looking for is an easy way to get some IO modules that are able to talk via ModBusTCP. This is an industrial protocoll that is existing in nearly any plc or scada of the world. ( made a modbus rtu driver for avr, near to assembler, in ca 98 ) And I'm deep into big installations and scada sw & applications.
    But this is privat and I simply have not the time to spend too many days into finding all tricks of a new sw/hw.
    My believe was that i have a chance to use some phyton and existing modbustcp modules and make an easy and dirty hack to have some handfull modules for my smarthome.

    I have an alternative product , oak, but that is arduino based and i guess it request even more effort.

  • @Mike-Eitel If you can wait a little, I'm sure there will be good step by step tutorials and/or ready-made docker containers for creating custom images eventually. Community members like @WereCatf and @Kit-Bishop have also done a lot, it's just it's still a bit experimental and some guesswork at the moment, as we are all dependent on @onion releasing their modifications.

    But once a clean setup is available, creating custom stripped down/enhanced images with LEDE will be really easy. All it needs is ~15GB of disk space and a few hours compiling time for the initial build, but I'd say no more than cutting&pasting five command lines total until your first installable Omega2-ready LEDE image is ready.

    So to help your own case and ours - just keep reminding @onion that they should release everything ASAP šŸ˜‰

  • THX Luz

    Yes, waiting seems best solution.
    If you know the multi millions of industrial devices using this protocol you understand why I see big potential, f.x in home automation, based on scada systems.

  • Modbus is a serial communications protocol originally published by Modicon in 1979 for use with its programmable logic controllers. Modbus has become a de facto standard communication protocol and is now a commonly available means of connecting industrial electronic devices visit official website

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