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Module API

The purpose of this tutorial is for writing new core modules that can be run on a device. In most cases, it is best to start with utilizing the serial module rather than creating a new one. However, if you're interested in creating a new core functionality from scratch, then building a module would be appropriate.

Key concepts​

All modules should be sub-classes of MeshModule. By inheriting from this class and creating an instance of your new module - your module will be automatically registered to receive packets.

Messages are sent to particular port numbers (similar to UDP networking). Your new module should eventually pick its own port number (see below). For development use, you can simply use PRIVATE_APP (which is the default).

Packets can be sent and received as either:

  1. Raw binary structures
  2. Protobufs.

Class hierarchy​

You will typically want to inherit from either SinglePortModule (if you are just sending/receiving raw bytes) or ProtobufModule (if you are sending/receiving protobufs). You'll implement your own handleReceived/handleReceivedProtobuf - probably based on the example code.

The relevant bits of the class hierarchy are as follows:

First Level: MeshModule​

Second Level: SinglePortModule​

Third Level: ProtobufModule​

  • src/mesh/ProtobufModule.h - for modules that send/receive a single particular Protobuf type. Inherit from this if you are using protocol buffers in your module.

Startup Operations​

If your module needs to perform any operations at startup you can override and implement the setup() method to run your code.

If you need to send a packet you can call service.sendToMesh with code like this (from the examples):

MeshPacket *p = allocReply();
p->to = dest;

service.sendToMesh(p);

Example Modules​

A number of key services are implemented using the Module API, These modules are as follows:

  • TextMessageModule - Receives text messages and displays them on the LCD screen/stores them in the local DB.

  • NodeInfoModule - Receives/sends User information to other nodes so that usernames are available in the databases.

  • RemoteHardwareModule - A module that provides easy remote access to device hardware (for things like turning GPIOs on or off). Intended to be a more extensive example and provide a useful feature of its own. See remote-hardware for details.

  • ReplyModule - A simple module that just replies to any packet it receives (provides a 'ping' service).

Getting started​

The easiest way to get started is:

  1. Build the firmware codebase.
  2. Copy the ReplyModule as a template into src/modules/. 
    cp src/modules/ReplyModule.* src/modules/YourModule.*
  3. Change the port number from PortNum_REPLY_APP to PortNum_PRIVATE_APP.
  4. Edit the setupModules() function located at modules/Modules.cpp to add a call to create an instance of your module (see comment at head of that function).
  5. Rebuild with your new module and install on the device.
  6. Use the Meshtastic Python CLI tool to send a packet to your board, for example:
    • meshtastic --dest 1234 --sendping where 1234 is another mesh node to send the ping to.

Threading​

It is very common that you would like your module to be invoked periodically. We use a crude/basic cooperative threading system to allow this on any of our supported platforms. Simply inherit from OSThread and implement runOnce(). See the OSThread documentation for more details.

Sending messages​

If you would like to proactively send messages (rather than just responding to them), just call service.sendToMesh(). For an example of this, see NodeInfoModule::sendOurNodeInfo(...).

Picking a port number​

See Meshtastic Port Numbers

How to add custom protocol buffers​

If you would like to use protocol buffers to define the structures you send over the mesh (recommended), here's how to do that.

  1. Create a new .proto file in the protos directory.
  2. Run ./bin/regen-protos.sh to regenerate the C code for accessing the protocol buffers. If you don't have the required nanopb tool, follow the instructions printed by the script to get it.
  3. Done! You can now use your new protobuf just like any of the existing protobufs in Meshtastic.