Digimesh support

[nlevnaut]

Feature request

Digimesh is not used as much as Zigbee, but it has some nice features and Digi has some long-range modules that use it. It would be very nice to have support for multiple XBee protocols built into exbee.

Zigbee VS Digimesh

XBee-PRO 2.4GHz Digimesh User Guide

XBee-PRO 900HP and XSC RF Modules User Guide

I believe their 900MHz and 2.4GHz modules have the same API mode... not 100% though.

I have a C implementation I've tested with their 900MHz modules on an ATMega328p here: atmega-xbee-digimesh. Most of the relevant stuff to look at for this project is in xbee.c and xbee.h. It's a bit bare-bones but API mode rx and tx both work.

[rockwood]

I think this should pretty easy to get working without needing any changes to Exbee. It looks like the digimesh and zigbee protocols are identical with just a different addressing scheme. Let's take the Transmit Request frame - 0x10 as an example. The Exbee.TxFrame has a network address and mac address. A digimesh compatible frame would have only a mac address.

defmodule MyDigiMeshTxFrame do
  defstruct [id: 0x01, mac_addr: 0x000000000000FFFF, radius: 0x00, options: 0x00, payload: nil]

  defimpl Exbee.EncodableFrame do
    alias Exbee.Util

    def encode(%{id: id, mac_addr: mac_addr, radius: radius, options: options, payload: payload}) do
      binary_payload = Util.to_binary(payload)
      <<0x10, id::8, mac_addr::64, 0xFFFE, radius::8, options::8, binary_payload::binary>>
    end
  end
end

And to use it:

iex> {:ok, pid} = Exbee.start_link(serial_port: "COM1", speed: 9600)
iex> Exbee.send_frame(pid, %MyDigiMeshTxFrame{mac_addr: ..., payload: ...})
:ok

I'd happily merge a PR that adds digimesh specific frames to Exbee.

[nlevnaut]

Ok, cool. I'm about halfway through the getting-started guide, but I've fallen down the Elixir rabbit hole and I'll look into adding Digimesh frames. :)

[rockwood]

@liberza I totally know the feeling. I started down the Elixir path a couple years ago and haven't looked back. It's a fantastic language, and I think you'll be very happy with it.

Let me know if you have any questions along the way. I'm @rockwood on Elixir Slack.

[nlevnaut]

I've added a new frame, Exbee.DigiMeshTxFrame. I only have one USB/serial adapter to test with at the moment, so I also created Exbee.DigiMeshTxResultFrame to test that TX works. I noticed I was never receiving the DigiMesh TX result, so I looked into Exbee.Message.

The DigiMesh TX result frame is slightly different than the ZigBee one, in that there are 2 reserved bytes after the frame ID in DigiMesh. They have the same frame ID though, which may make things interesting. I see in Exbee.Message, the decodable frames are mapped by ID.

I'm thinking that perhaps the IDs in @decodable_frames could map to tuples containing the different "flavors" of frame that use that ID. Like this:

@decodable_frames %{
    0x88 => {Exbee.ATCommandResultFrame},
    0x8A => {Exbee.DeviceStatusFrame, Exbee.DigiMeshDeviceStatusFrame},
    0x8B => {Exbee.TxResultFrame, Exbee.DigiMeshTxResultFrame},
    0x90 => {Exbee.RxFrame, Exbee.DigiMeshRxFrame},
    0x91 => {Exbee.ExplicitRxFrame, Exbee.DigiMeshExplicitRxFrame},
    0x92 => {Exbee.RxSampleReadFrame},
    0x94 => {Exbee.RxSensorReadFrame},
    0x97 => {Exbee.RemoteATCommandResultFrame},
  }

Then just attempt decoding a frame with each frame type in the tuple, until the end or until one works.

The other way I thought of doing it is by just requiring the user to specify that they are using DigiMesh, and only attempt decoding DigiMesh frames in that case.

[nlevnaut]

Wait. Something smells here. The reserved portion of the DigiMesh frames is the same spot that the network address would be in ZigBee frames. Your default network_addr is 0xFFFE, so using Exbee.TxFrame without a network_addr specified should give us a DigiMesh frame.

Same with the TxResultFrame. The Digi documentation for the 900HP appears to have a typo in their table that is a bit misleading.

So... exbee should already support DigiMesh frames! I can test once I receive my new USB/serial adapter.

[rockwood]

@liberza Yeah, I guess that would make sense if they both use the same frame type identifier. I assume they anticipated a network having both Xbee and Digimesh modules. Let me know if that works when you find out more.

[nlevnaut]

Looks like it sort-of works! I had some weird settings on my XBees from a while back, but I reset them to factory mode and TxFrame appears to be compatible. TxResultFrame is received intact as well. The checksum seems to fail for receive though. I'll dig into that.

[rockwood]

@liberza Great! Yeah, my use case for creating Exbee was pretty limited so I haven't thoroughly tested every frame type. Please send me a PR if you find any problems.

[rockwood]

Closing for now