README.md

Exmbus

---

Elixir M-Bus & Wireless M-Bus (wM-bus) parser library.

Installation

The package can be installed by adding exmbus to your list of dependencies in mix.exs:

def deps do
  [
    {:exmbus, "~> 0.2.0"}
  ]
end

Features

• M-bus
• wM-bus
• TPL Encryption modes: 0, 5
• (partly) supports ELL (supports encryption modes: 0 (none), 1 (aes_128_ctr)
• Compact Frames and Format Frames
• Compact Profiles
• VIF extension tables 0xFD and 0xFB (with a few exceptions)

Feature Requests

If you'd like a specific device supported, open an issue and attach or link to the datasheet for the device.
If you can provide data from a real test device even better.

No effort will be made towards supporting a device without an example of a payload from the device (either from the datasheet or real world capture)

Important

Under no circumstances should you publish data to the issue tracker or repository from a device that is actually deployed, as those might contain PII or other sensitive information. The same is true encryption keys where the key might potentially be used in more than once device.

Planned

• Transition the parser fully to handler + context based, and avoid raising on error but instead attach an error to the context. The APL layer in particular needs a lot of work here.
• Better API for encryption key storage.
• DLL CRC support.
• Split parsing and decoding into two steps. Currently the code parses the binary and decodes it in the same walk, but this causes errors when we can't decode an unsupported feature.

Not Planned

• Authentication and Fragmentation layer CI=90

Performance

It's fine.

You can run the benchmarks under benchmarks/ to get an idea of the performance on the relevant hardware.

You should test on frames that matches your deployment scenario, but if you just want a rough estimate, there is a benchmark using an example frame from OMS Vol2 Annex N:

mix run benchmarks/oms_vol2_annex_n.exs

Here are the results we've gathered so far for the "With input N.2.1. wM-Bus Meter with Security profile A" bench

Hardware	ips	average	deviation	median	99th %
Apple 12 core M3 Pro 36GB	289.61 K	3.45 μs	±63.73%	3.13 μs	7.21 μs

Examples

Parse wM-Bus

This is an example from the OMS Vol2 Annex N - N.2.1. wM-Bus Meter with Security profile A

Exmbus.parse! will return an Exmbus.Parser.Context struct as the result.

iex> "2E4493157856341233037A2A0020255923C95AAA26D1B2E7493B013EC4A6F6D3529B520EDFF0EA6DEFC99D6D69EBF3"
...> |> Base.decode16!()
...> |> Exmbus.parse!(key: Base.decode16!("0102030405060708090A0B0C0D0E0F11"))
%Exmbus.Parser.Context{
  bin: "",
  opts: %{
    length: false,
    key: <<1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 17>>,
    crc: false
  },
  handlers: [],
  handler: &Exmbus.Parser.Apl.FullFrame.maybe_expand_compact_profiles/1,
  dll: %Exmbus.Parser.Dll.Wmbus{
    control: :snd_nr,
    manufacturer: "ELS",
    identification_no: 12345678,
    version: 51,
    device: :gas
  },
  ell: %Exmbus.Parser.Ell.None{},
  tpl: %Exmbus.Parser.Tpl{
    frame_type: :full_frame,
    header: %Exmbus.Parser.Tpl.Header.Short{
      access_no: 42,
      status: %Exmbus.Parser.Tpl.Status{
        manufacturer_status: 0,
        temporary_error: false,
        permanent_error: false,
        low_power: false,
        application_status: :no_error
      },
      configuration_field: %Exmbus.Parser.Tpl.ConfigurationField{
        hop_count: 0,
        repeater_access: 0,
        content_of_message: 0,
        mode: 5,
        syncrony: true,
        accessibility: false,
        bidirectional: false,
        blocks: 2
      }
    }
  },
  apl: %Exmbus.Parser.Apl.FullFrame{
    records: [
      %Exmbus.Parser.Apl.DataRecord{
        header: %Exmbus.Parser.Apl.DataRecord.Header{
          dib_bytes: "\f",
          vib_bytes: <<20>>,
          dib: %Exmbus.Parser.Apl.DataRecord.DataInformationBlock{
            device: 0,
            tariff: 0,
            storage: 0,
            function_field: :instantaneous,
            data_type: :bcd,
            size: 32
          },
          vib: %Exmbus.Parser.Apl.DataRecord.ValueInformationBlock{
            description: :volume,
            multiplier: 0.01,
            unit: "m^3",
            extensions: [],
            coding: nil,
            table: :main
          },
          coding: :type_a
        },
        data: 2850427
      },
      %Exmbus.Parser.Apl.DataRecord{
        header: %Exmbus.Parser.Apl.DataRecord.Header{
          dib_bytes: <<4>>,
          vib_bytes: "m",
          dib: %Exmbus.Parser.Apl.DataRecord.DataInformationBlock{
            device: 0,
            tariff: 0,
            storage: 0,
            function_field: :instantaneous,
            data_type: :int_or_bin,
            size: 32
          },
          vib: %Exmbus.Parser.Apl.DataRecord.ValueInformationBlock{
            description: :naive_datetime,
            multiplier: nil,
            unit: nil,
            extensions: [],
            coding: :type_f,
            table: :main
          },
          coding: :type_f
        },
        data: ~N[2008-05-31 23:50:00]
      },
      %Exmbus.Parser.Apl.DataRecord{
        header: %Exmbus.Parser.Apl.DataRecord.Header{
          dib_bytes: <<2>>,
          vib_bytes: <<253, 23>>,
          dib: %Exmbus.Parser.Apl.DataRecord.DataInformationBlock{
            device: 0,
            tariff: 0,
            storage: 0,
            function_field: :instantaneous,
            data_type: :int_or_bin,
            size: 16
          },
          vib: %Exmbus.Parser.Apl.DataRecord.ValueInformationBlock{
            description: :error_flags,
            multiplier: nil,
            unit: nil,
            extensions: [],
            coding: :type_d,
            table: :fd
          },
          coding: :type_d
        },
        data: [false, false, false, false, false, false, false, false, false,
         false, false, false, false, false, false, false]
      }
    ],
    manufacturer_bytes: ""
  },
  dib: nil,
  vib: nil,
  errors: [],
  warnings: []
}

Testing

mix test

Profiling

Some profiling scripts are available under profiling/.

You can run then with e.g. eprof:

 mix profile.eprof profiling/oms_vol2_annex_n.exs